FLS2023 - Classification: A - Linac-based Light Sources

Paper	Title	Page
MO1L3	Production and Characterization of Hard X-rays Beyond 25 keV
	Y. Chen, T. Long DESY, Hamburg, Germany
	Dedicated R&D programs, aimed for delivering ultra-hard X-rays beyond 25 keV for advanced user experiments, have been launched at the European XFEL. Characterization of the electron beam and the photon beam transport to the instrumentation have been carried out. Given the very first experiments, optimized SASE intensities of 0.8 mJ at 24.58 keV and 0.3 mJ at 30.24 keV, both lasing at the fundamentals, have been simultaneously demonstrated at two hard X-ray beamlines of the facility. These experiments were carried out using optimized low-emittance electron beams based on existing undulators with a 4 cm period and 16.4 GeV electron beam energy. It has also been shown, that the transport of 30 keV photon beams to the user experiments was made possible. The obtained results will be presented. Further discussions on the realization of ultra-hard X-rays using advanced techniques, as well as improved longitudinal beam diagnostics of the facility will be given in detail.
	Slides MO1L3 [8.172 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A1	Progress on SHINE Machine
	D. Wang SINAP, Shanghai, People’s Republic of China
	SHINE (Shanghai HIgh repititioN rate hard x-ray free electron laser and Extreme light) is a superconducting linac-based free electron laser facility. It consists of a cw VHF electron gun, 75 8-cavity cryomodules, fast beam distributions, 3 FEL undulator lines as well as the photon beam lines/end-stations. In this talk we will give an introduction to the latest progress of the machine part of this project. Supported by the project funding (including the R&D and construction money that come up at same time) extensive prototyping has been conducted on major components like high rep-rate gun, cavities/cryomodules for cw linac, large cryogenic plant, fast kickers and undulators, among others. The cw beam test facility was set up to operate at cw mode for electron gun and cryomocules.
	Slides MO3A1 [11.431 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A2	Status and Perspectives for the Swiss Free-Electron Laser (SwissFEL)	26
	T. Schietinger PSI, Villigen PSI, Switzerland
	We summarize the status of SwissFEL, the X-ray free-electron laser at the Paul Scherrer Institute. Apart from some key operational performance figures the presentation covers the state of the experimental stations and their capabilities, gives a few scientific highlights and an overview of the use of special modes beyond SASE at our facility. Furthermore we report on progress of our seeding upgrade program on the soft X-ray line. Lastly we mention our long-term upgrade plans for a third undulator beamline in the tender and hard X-ray regime.
	Slides MO3A2 [8.398 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-MO3A2
About •	Received ※ 29 August 2023 — Revised ※ 30 August 2023 — Accepted ※ 30 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A3	Status of the LCLS-II Superconducting Linac
	D. Gonnella SLAC, Menlo Park, California, USA
	Funding: US DoE The LCLS-II project installed a new superconducting linac into the existing SLAC tunnel to enable a high repetition rate x-ray FEL. Over the last 1.5 years, the commissioning of the new linac has taken place and been overall very successful. The status of the commissioning and experience from early operations of the new superconducting linac will be presented.
	Slides MO3A3 [5.118 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A4	European XFEL Status Overview
	M. Scholz DESY, Hamburg, Germany
	Since its launch in 2017, European XFEL has been operating reliably and stably, delivering photons to user experiments. The range of services, the overall performance and the provision of special operating modes have been continuously improved. Its superconducting accelerator delivers up to 27000 electron bunches per second in a 10 Hz pulsed mode to 3 undulator beamlines, which in turn can deliver photons to one of two associated instruments. The high electron beam energy of up to 17.5 GeV predestines this facility for high photon energies up to 30 keV. In addition to the default delivery modes, the user community is increasingly requesting other modes of operation such as self-seeding, very short pulses, two colours or customised bunch distributions in the individual pulse trains. We will present a brief summary of the current status of the different operating modes and give an outlook into the future.
	Slides MO3A4 [11.059 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A5	FLASH: Status and Upgrade	32
	M. Vogt, S. Schreiber, J. Zemella DESY, Hamburg, Germany
	FLASH, the Soft X-Ray and Extreme-UV Free Electron Laser at DESY, is undergoing a substantial upgrade and refurbishment project, called FLASH2020+. The project will finally enable external seeded and SASE FEL operation for a wavelength range down to 4 nm with the EEHG method. This is achieved in two long shutdowns from November 2021 to August 2022 and from June 2024 to August 2025. Key ingredient of the upgrade were installation of a laser heater, replacing two early TTF-type L-band SRF accelerating modules by modern, high-gradient XFEL-type modules, redesign of the 2nd bunch compressor, and complete redesign of the FLASH1 beam line for HGHG/EEHG seeding. This talk will report on the project and the status of FLASH after the first shutdown with emphasis on beam dynamics aspects.
	Slides MO3A5 [1.108 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-MO3A5
About •	Received ※ 25 August 2023 — Revised ※ 26 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A6	Recent status of PAL-XFEL
	M.H. Cho, I. Eom, H. Heo, H.-S. Kang, C.-K. Min, I.H. Nam, J. Park, S.H. Park, C.H. Shim, H. Yang PAL, Pohang, Republic of Korea
	Since opened to users in 2017, significant progress of PAL-XFEL has been made in operations including increasing the FEL pulse energy and the FEL photon energy, generating stable and high power self-seeding FELs, and two-color FELs. In the beamline, new instruments or endstations have been added such as the femtosecond X-ray scattering (FXS) with 800 nm laser pulse, the X-ray absorption spectroscopy (SAX), the serial femtosecond crystallography (SFX) with operation with developed noble sample-delivery-systems, Fourier-Transform Holography (FTH), and so on. Overall, beamline operation has enabled excellent scientific results through efficient user experiments. This talk will introduce recent status of PAL-XFEL and show representative experiment results shortly.
	Slides MO3A6 [3.739 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A7	Present Status of SACLA and Plans for Future Upgrades
	T. Inagaki, T. Hara, E. Iwai, C. Kondo, H. Maesaka, H. Tanaka RIKEN SPring-8 Center, Hyogo, Japan
	SACLA has two XFEL beamlines, BL3 and BL2, which are driven by an 8-GeV normal-conducting C-band high-gradient accelerator and provide SASE from 4 keV to 20 keV, and an EUV-FEL beamline BL1, which is driven by an 800-MeV accelerator and provides SASE from 40 eV to 150 eV. To perform the parallel operation of BL3 and BL2 and the top-up injection into the SPring-8 storage ring, the electron gun, accelerating RF, focusing magnets, and switchyard magnets are synchronously controlled for each 60 Hz pulse. In recent years, experiments using special FELs such as reflection-type self-seeded FELs, two-color, double-pulsed FELs, ultra-short pulsed FELs and nano-focusing optics have been conducted at XFEL beamlines. In order to supply XFELs tailored to various experimental conditions, an automatic tuning system of the accelerator using machine learning has been established and is used for daily tuning. In the future, we plan to improve and precisely control the characteristics of the FEL, such as intensity, pulse duration, spectrum, photon energy, and pulse repetition rate. To achieve these goals, we are working on 1) refinement of accelerator models using electron beam monitors and machine learning, 2) development of the electron gun to increase the beam brightness, 3) development of the efficient RF acceleration. For the purpose of 3, we have started to study a new normal-conducting accelerator design, with the goal of increasing the pulse repetition rate while maintaining XFEL performance and power consumption, to be consistent with ¿Green Facility¿ declaration. In this presentation, we introduce the status and future plans for upgrading SACLA.
	Slides MO3A7 [1.161 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A8	FERMI FEL Upgrade Plans, an Overview
	S. Di Mitri, E. Allaria, L. Badano, P. Cinquegrana, I. Cudin, G. D’Auria, M.B. Danailov, G. De Ninno, P. Delgiusto, A.A. Demidovich, D. Garzella, L. Giannessi, C. Masciovecchio, G. Penco, P. Rebernik Ribič, N. Shafqat, P. Sigalotti, C. Spezzani, L. Sturari, M. Trovò Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy G. De Ninno University of Nova Gorica, Nova Gorica, Slovenia L. Giannessi LNF-INFN, Frascati, Italy
	Short and long term upgrade plans of the FERMI free-electron laser facility at Elettra Sincrotrone Trieste, Italy, will be reported. They include the ongoing linear accelerator energy upgrade and the conversion of the first undulator line to echo-enabled harmonic generation. The upgrade of the second undulator line to a two stage echo-based fresh-bunch scheme is also under study.
	Slides MO3A8 [1.847 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A9	Comissioning Progress and Advanced FEL Experiments at the SXFEL Facility
	C. Feng, B. Liu, Z. Wang, Z.T. Zhao SARI-CAS, Pudong, Shanghai, People’s Republic of China
	The Shanghai soft X-ray Free-Electron Laser facility (SXFEL) is the first X-ray FEL facility in China. The construction of the SXFEL facility was finished in 2022. The output photon energy of the SXFEL can cover the whole water window range. Except for the self-amplified spontaneous emission, various seeding technques have also been adopted for improving the performances of the SXFEL. Here we presents an overview of the SXFEL facility, including the layout and design, construction status, commissioning progress and future plans on advanced FEL experiments.
	Slides MO3A9 [4.688 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU2A1	Coherent Free-electron Laser Pulses: The User Perspective
	G. De Ninno Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Are fully-coherent pulses the Holy Grail for experiments, which aim at taking full advantage of the properties of a free-electron laser (FEL)? What are the strategies to generate and diagnose them at seeded FEL facilities? What are the requirements for experiments based on pulse shaping and coherent control? How goes it for quantum coherence and the possibility to generate FEL pulses with sub-Poissonian statistics? We will talk about all this and more.
	Slides TU2A1 [1.584 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU2A2	Single Longitudinal Mode Generation in Slippage-dominated, Tapered-undulator SASE Soft X-ray FEL	70
	D.C. Nguyen, M. Dunham, W. Lou, C.E. Mayes, G. Stupakov xLight, Palo Alto, USA
	SASE FELs operating in the soft X-ray region exhibit multiple temporal and spectral spikes with an overall spectral bandwidth of about 1.5 times the FEL rho parameter. While many ideas have been proposed to achieve fully coherent X-ray FELs, only monochromatic seeding, either harmonic seeding* or SASE self-seeding*, has been experimentally demonstrated to narrow the output spectra of soft X-ray FELs. In this paper, we study a different method that relies on the Slippage-dominated Tapered Undulator (STU) SASE concept to produce a single longitudinal mode in a soft X-ray FEL driven by ~10-fs, 16-pC electron bunches. We pre-sent numerical simulation results that demonstrate single-mode generation and narrow-lined spectra without seeding in a STU-SASE FEL at 6.67 nm. E. Alaria et al., Nat Photon 7 (2013) 913-918 ** D. Ratner et al., PRL 114 (2015) 050801
	Slides TU2A2 [1.125 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU2A2
About •	Received ※ 22 August 2023 — Revised ※ 23 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU2A3	Opportunities and Challenges of the Hard X-ray Self-seeding System at the European XFEL
	S. Liu, P. Dijkstal, C. Grech, M.W. Guetg, V. Kocharyan, T. Long, N.S. Mirian, W. Qin DESY, Hamburg, Germany G. Geloni, N.G. Kujala, C. Lechner, S. Serkez, J.W. Yan EuXFEL, Schenefeld, Germany
	The Hard X-ray Self-seeding system (HXRSS) at the European XFEL provides users with longitudinally coherent X-ray FEL pulses with narrow bandwidth and high spectral density. With this setup we have achieved a maximum spectral density of about 1 mJ/eV at 9 keV. Combined with the MHz repetition rate, it opens up exciting new opportunities in a wide range of scientific fields. However, the increasing user demand and expectations also poses challenges in machine tuning and operation parameter ranges. We will summarize the HXRSS performance we have achieved and the user delivery experiences in the last two years.
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU2A4	A Low-loss 14 m Hard X-ray Bragg-reflecting Cavity, Experiments and Analysis
	R.A. Margraf, Z. Huang, R. Robles Stanford University, Stanford, California, USA A. Halavanau, Z. Huang, J. Krzywiński, K. Li, J.P. MacArthur, G. Marcus, R. Robles, A. Sakdinawat, T. Sato, Y. Sun, D. Zhu SLAC, Menlo Park, California, USA T. Osaka, K. Tamasaku RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
	Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515. Bragg-reflecting cavities on the 10 s or 100 s of meter scale are a core component of proposed Cavity-Based X-ray Free-Electron Lasers (CBXFELs). While CBXFELs promise improved longitudinal coherence and spectral brightness over single-pass self-amplification of spontaneous radiation (SASE) FELs, construction and alignment of large Bragg-reflecting cavities can be difficult technical challenge. Our collaboration recently demonstrated stable operation of a low-loss 14 m 9.831 keV X-ray cavity of four Bragg-reflecting diamond mirrors, a significant step towards a CBXFEL-scale cavity. We in-coupled X-rays from the Linac Coherent Light Source (LCLS) into our cavity via a transmission grating, then measured round-trip efficiencies approaching 88%, or >96% when neglecting losses on in-coupling and focusing optics. Additionally, we characterized transverse oscillations in the cavity, demonstrating the effectiveness of our cavity focusing. We will discuss these results, additional new analysis and consider implications for future CBXFEL projects. R. Margraf et al., ‘Low-loss Stable Storage of X-ray Free Electron Laser Pulses in a 14 m Rectangular Bragg Cavity’, In Review, preprint, 2023. doi: 10.21203/rs.3.rs-2465216/v1.
	Slides TU2A4 [3.245 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P05	Design of the Test Platform for High Current VHF Electron Gun	80
	Z.P. Liu, X.D. Li SINAP, Shanghai, People’s Republic of China H.X. Deng, Z.G. Jiang SARI-CAS, Pudong, Shanghai, People’s Republic of China H.J. Qian DESY Zeuthen, Zeuthen, Germany G. Shu IHEP, Beijing, People’s Republic of China
	A high-average-current VHF electron gun operating in the CW mode is under construction at Shanghai Advanced Research Institute, which is the key component of a kW-power-order free electron laser facility. The average current and the frequency of this electron gun is 1-10 mA and 217 MHz, respectively. To validate the performance of this instrument, a test platform has been designed. The R&D of its vacuum and diagnostics are presented in this work.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P05
About •	Received ※ 23 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P06	The Experimental Progress for the Strong Field Terahertz Radiation at Shanghai Soft X-ray Free-electron Laser Facility	83
	K.Q. Zhang, C. Feng SSRF, Shanghai, People’s Republic of China Y. Kang SINAP, Shanghai, People’s Republic of China
	Strong field Terahertz (THz) light source has been in-creasingly important for many scientific frontiers, while it is still a challenge to obtain THz radiation with high pulse energy at wide-tunable frequency. In this paper, we introduce an accelerator-based strong filed THz light source to obtain coherent THz radiation with high pulse energy and tunable frequency and X-ray pulse at the same time, which adopts a frequency beating laser pulse modulated electron beam. Here, we present the experi-mental progress for the strong filed THz radiation at shanghai soft X-ray free-electron laser (SXFEL) facility and show its simulated radiation performance.
	Poster TU4P06 [1.310 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P06
About •	Received ※ 21 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P07	Design of the Beam Distribution System of SHINE	87
	S. Chen SSRF, Shanghai, People’s Republic of China H.X. Deng, X. Fu, B. Liu SARI-CAS, Pudong, Shanghai, People’s Republic of China B.Y. Yan SINAP, Shanghai, People’s Republic of China
	The Shanghai high-repetition-rate XFEL and extreme light facility (SHINE), as the first hard X-ray free electron laser facility in China, is now under construction. CW electron beam with up to 1 MHz bunch repetition rate from a superconducting RF linac is used to feed at least three individual undulator lines that covers a wide photon energy range (0.4 keV ~ 25 keV). In order to maximize the efficiency of the facility, a beam switchyard between the linac and undulator lines is used to enable the simultaneously operation of the three undulator lines. In this work, the schematic design of the beam switchyard for bunch-by-bunch beam separation of CW beam is described, and the current lattice design of the linac-to-undulator deflection branches and the start-to-end tracking simulation results are presented.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P07
About •	Received ※ 22 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P08	Design and Commissioning of the Beam Switchyard for the SXFEL-UF	91
	S. Chen, K.Q. Zhang SSRF, Shanghai, People’s Republic of China H.X. Deng, C. Feng, B. Liu, T. Liu, Z. Qi, Z.T. Zhao SARI-CAS, Pudong, Shanghai, People’s Republic of China
	As an important measure of improving the efficiency and usability of X-ray free electron laser facilities, parallel operation of multiple undulator lines realized by a beam switchyard has become a standard configuration in the recent built XFEL facilities. SXFEL-UF, the first soft X-ray free electron laser user facility in China, has finished construction and commissioning recently. The electron beams from the linac are separated and delivered alternately to the two parallel undulator beam lines through a beam switchyard. A stable and fast kicker magnet is used to achieve bunch-by-bunch separation. Optics measures are applied to mitigate the impact of various collective effects, such as coherent synchrotron radiation and micro-bunching instability, on the beam quality after passing through the deflection line of the beam switchyard. In this study, the comprehensive physical design of the beam switchyard is described and the latest results of its commissioning process are presented.
	Poster TU4P08 [4.643 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P08
About •	Received ※ 23 August 2023 — Revised ※ 30 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P11	Symmetric Compton Scattering: A Way Towards Plasma Heating and Tunable Mono-chromatic Gamma-rays	95
	L. Serafini, A. Bacci, I. Drebot, M. Rossetti Conti, S. Samsam INFN-Milano, Milano, Italy C. Curatolo INFN- Sez. di Padova, Padova, Italy V. Petrillo, A. Puppin Universita’ degli Studi di Milano & INFN, Milano, Italy
	We analyze the transition between Compton Scattering and Inverse Compton Scattering (ICS), characterized by an equal exchange of energy and momentum between the colliding particles (electrons and photons). In this Symmetric Compton Scattering (SCS) regime, the energy-angle correlation of scattered photons is cancelled, and, when the electron recoil is large, monochromaticity is transferred from one colliding beam to the other. Large-recoil SCS or quasi-SCS can be used to design compact intrinsic monochromatic γ-ray sources based on compact linacs, thus avoiding the use of GeV-class electron beams and powerful laser/optical systems as required for ICS sources. At very low recoil and energy collisions (about 10 keV energy range), SCS can be exploited to heat the colliding electron beam, which is scattered with large transverse momenta over the entire solid angle, offering a technique to trap electrons into magnetic bottles for plasma heating.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P11
About •	Received ※ 24 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P12	Injection Into XFELs, a Review of Trends and Challenges	99
	C. Davut UMAN, Manchester, United Kingdom Ö. Apsimon Cockcroft Institute, Warrington, Cheshire, United Kingdom B.L. Militsyn, S.S. Percival STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: Science and Technology Facilities Council, STFC In this contribution, we review the low-energy electron injectors for existing X-ray Free-Electron Laser (XFEL) facilities focusing on the buncher and booster sections. The technology choices are parallel to the increasing demand for stricter six-dimensional phase space quality. The current capability for beam parameters and future requirements are laid out alongside a discussion on challenges and technological bottlenecks. In light of this review, preliminary results for a high capability injector providing high repetition rate, and continuous wave emission is presented as an option for the UK XFEL.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P12
About •	Received ※ 23 August 2023 — Revised ※ 24 August 2023 — Accepted ※ 30 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P13	An Introduction to the UK XFEL Conceptual Design and Options Analysis	103
	D.J. Dunning, D. Angal-Kalinin, J.A. Clarke, J. Henderson, S.L. Mathisen, B.L. Militsyn, M.D. Roper, E.W. Snedden, N. Thompson, D.A. Walsh, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom P. Aden, B.D. Fell STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom D. Angal-Kalinin, J.A. Clarke, D.J. Dunning, J. Henderson, B.L. Militsyn, N. Thompson, P.H. Williams Cockcroft Institute, Warrington, Cheshire, United Kingdom J.L. Collier, J.S. Green STFC/RAL, Chilton, Didcot, Oxon, United Kingdom J.P. Marangos Imperial College of Science and Technology, Department of Physics, London, United Kingdom
	In October 2022, the UK XFEL project entered a new phase to explore how best to deliver the advanced XFEL capabilities identified in the project’s Science Case. This phase includes developing a conceptual design for a unique new machine to fulfil the required capabilities and more. It also examines the possibility of investment opportunities at existing XFELs to deliver the same aims, and a comparison of the various options will be made. The desired next-generation capabilities include transform-limited operation across the entire X-ray range with pulse durations ranging from 100 as to 100 fs; evenly spaced high rep. rate pulses for enhanced data acquisition rates; optimised multi-colour FEL pulse delivery and a full array of synchronised sources (XUV-THz sources, electron beams and high power/high energy lasers). The project also incorporates sustainability as a key criteria. This contribution gives an overview of progress to date and future plans.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P13
About •	Received ※ 23 August 2023 — Revised ※ 25 August 2023 — Accepted ※ 30 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P16	Transverse Optics-based Control of the Microbunching Instability	107
	A.D. Brynes, E. Allaria, G. De Ninno, S. Di Mitri, D. Garzella, C. Spezzani Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy G. De Ninno University of Nova Gorica, Nova Gorica, Slovenia G. Perosa Università degli Studi di Trieste, Trieste, Italy C.-Y. Tsai HUST, Wuhan, People’s Republic of China
	A number of recent experimental and theoretical studies have investigated novel techniques for suppressing the microbunching instability in high-brightness linac-based light sources. This instability has long been studied as one of the causes of reduced longitudinal coherence in these machines, which are commonly suppressed using a laser heater. This contribution presents recent developments concerning the use of an optics-based scheme to mitigate the microbunching instability in the FERMI free-electron laser, paving the way towards reversible beam heating techniques that could improve the performance of future machines.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P16
About •	Received ※ 23 August 2023 — Revised ※ 29 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE1L1	Status and Future of XFEL Source Developments
	S. Reiche PSI, Villigen PSI, Switzerland
	Since the first demonstration of the SASE principle in the X-ray regime, there has been an ongoing development on improving and controlling the properties of the generated X-ray FEL pulses. This presentation gives a brief status on these efforts and an outlook of possible improvements in the future.
	Slides WE1L1 [4.884 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE1L2	Progress of Cavity-based X-ray Free-electron Lasers
	Z. Huang SLAC, Menlo Park, California, USA
	Cavity-based X-ray Free electron lasers (FELs) such as the X-ray regenerative amplifier FEL (XRAFEL)* and the X-ray FEL oscillator (XFELO) have been proposed to produce temporally coherent and stable hard X-ray pulses, especially for high-repetition rate FEL facilities. An X-ray cavity consisting of Bragg crystals will be used to recirculate the spectrally filtered X-rays for repetitive interactions with an electron bunch train and to generate high-power and narrow-bandwidth radiation. In this talk, we review the scientific motivation and recent progress of Cavity-based X-ray FELs. We discuss cavity designs, optics requirements, outcoupling schemes, and the latest experimental results. Finally, we introduce the ongoing RD projects at LCLS* and European XFEL**** to prove the concept, as well as several Cavity-based proposals to enhance X-ray FEL’s spectral brightness by another two to three orders of magnitude compared to the state of art. * Z. Huang and R.D. Ruth, Phys. Rev. Lett. 96, 144801 (2006). K.-J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008). * K.J. Kim et al., Cavity-based XFEL R&D Project, this workshop. **** P. Rauer et al., Phys. Rev. Accel. Beams 26, 020701 (2023).
	Slides WE1L2 [5.251 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE2A1	Modified Maxwell-Bloch Equations for X-ray Amplified Spontaneous Emission in X-ray Lasers
	K.-J. Kim, R.R. Lindberg, J.-W. Park ANL, Lemont, Illinois, USA
	Funding: This work is supported by the U.S. Department of Energy, Office of Science under Contract No. DE-AC02-06CH11357. Observations of stimulated emission in atomic media pumped by X-ray FELs have shown that X-ray lasers may be possible using the physical process referred to amplified spontaneous emission(ASE). The coherence and stability of an ASE-based X-ray laser can be improved in an X-ray laser oscillator (XLO)* by employing an X-ray cavity as in the X-ray FEL oscillator (XFELO). We present a Hamiltonian-based, 3D theory in paraxial approximation. Assuming factorization of operator products, the ensemble-averaged Heisenberg equations become Maxwell-Bloch equations which provide a correct description of the stimulated emission. The spontaneous emission is accounted for by adding a random noise term to the atomic coherence, which is uniquely determined from the fact that factorization does not apply for products of operators associated with the same atom. Our theory reproduces the results of the previous 1D theory and extends it in including the 3D diffraction effects, in including the seed field, and in incorporating the noise in more versatile way. It provides a sound numerical framework to evaluate an X-ray laser, either in single pass or oscillator configurations. A. Halavanau, et al., PNSA 117, 27 (2020). A. Benediktovitch, et al., Phys. Rev. A 99, 013839 (2019) * J.-W. Park, K.-J. Kim, and R. Lindberg, Phys. Rev. Lett., submitted
	Slides WE2A1 [1.179 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE2A2	An Analytical Method for Longitudinal Phase Space Backtracking
	N.S. Sudar, Y. Ding SLAC, Menlo Park, California, USA
	Electron beam driven light sources require a longitudinal phase space exhibiting narrow energy spread and high peak current. In linear accelerators this is typically realized by employing multiple stages of bunch compression coupled with various techniques to shape the electron beam chirp. Increases in repetition rate limit many of these manipulations due to the high average beam power. This encourages manipulation of the electron beam properties at the source or low energy area of the accelerator. However, determining the upstream phase space properties that will lead to a particular final phase space proves difficult due to the many free variables of the accelerator and collective effects. Here we present an analytical method for tracking polynomial coefficients describing the final electron beam chirp and current profile backwards to an upstream point in the accelerator. This is written to arbitrary polynomial order and includes analytical expressions for collective effects. The method is applied to the LCLS-II linac, tracking from the undulator entrance back to the injector exit. The example case provided here leads to a 4 kA peak current flat top distribution and 0.1% RMS energy spread at the undulator entrance, representing a significant increase in the LCLS-II beam brightness. Forward tracking in Elegant of the found ideal distribution at the injector exit and accelerator configuration shows good comparison.
	Slides WE2A2 [4.564 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE2A3	A Wiggler-based THz Source at LCLS-II and Studies for a 150-m THz Transport Line for Pump-probe Experiments
	M. Henstridge, A.S. Fisher, M.C. Hoffmann, Z. Huang SLAC, Menlo Park, California, USA
	Ultrafast THz pulses with energies of several µJ drive exotic non-equilibrium phenomena in complex materials, yet many of the underlying microscopic mechanisms remain unknown. Current strong-field THz sources rely mostly on difference-frequency mixing of near-infrared laser pulses in crystals at few-kHz repetition rates, but the extension of such sources to higher repetition rates suffers from reduced pulse energies and crystal damage. Here, we present a wiggler-based THz scheme capable of delivering 3-30 THz pulses with energies of 100 µJ at the 100 kHz rate supported by LCLS-II. Two time-delayed electron bunches independently drive the wiggler and x-ray undulator to generate precisely synchronized and optimized x-ray and THz pulses for pump-probe experiments. We built a model transport line to address the significant challenge of transporting the THz emission over the minimum 150-m distance necessary to reach the experimental halls. This concept, scaled to 12-m, has been tested with the 28 THz output of a CO₂ laser. Results indicate that the THz emission can be transported over 150-m with an efficiency near 90%. Further testing is underway at 3.5 THz with a quantum-cascade laser.
	Slides WE2A3 [1.066 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE2A4	Scaling of Beam Collective Effects with Bunch Charge in the CompactLight Free-electron Laser
	S. Di Mitri, G. D’Auria, R.A. Rochow Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy M. Aicheler HIP, University of Helsinki, Finland A. Aksoy Ankara University, Accelerator Technologies Institute, Golbasi, Turkey D. Alesini, M. Diomede, M. Ferrario, A. Gallo, A. Giribono, J. Scifo, B. Spataro, C. Vaccarezza, A. Vannozzi LNF-INFN, Frascati, Italy G. Burt Lancaster University, Lancaster, United Kingdom H.M. Castañeda Cortés, J.A. Clarke, D.J. Dunning, N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J.A. Clarke, D.J. Dunning, N. Thompson Cockcroft Institute, Warrington, Cheshire, United Kingdom M. Croia ENEA Casaccia, Roma, Italy V.A. Goryashko Uppsala University, Uppsala, Sweden A. Latina, X.W. Wu, W. Wuensch CERN, Meyrin, Switzerland A. Mostacci Sapienza University of Rome, Rome, Italy F. Nguyen ENEA C.R. Frascati, Frascati (Roma), Italy
	The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges in the range 75-300 pC. Space-charge forces in the injector, linac transverse wakefield, and coherent synchrotron radiation in bunch compressors are all taken into account. The study confirms efficient lasing in the soft X-rays regime with pulse energies up to hundreds of microjoules at repetition rates as high as 1 kHz.
	Slides WE2A4 [1.777 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A1	High Pulse Rate Experiments at the European X-ray Free-electron Laser
	R. Letrun EuXFEL, Schenefeld, Germany
	The rise of superconducting accelerator technology has brought forth an increase in the pulse rate produced by X-ray free-electron lasers (XFELs) by two orders of magnitude, up to now, with a further increase on the horizon at new and existing facilities. The high pulse rate has opened up new opportunities for the scientific community, not only in terms of the volume of data that can be acquired, but also in the design of experiments that leverage the high pulse rate. However, these advances come with new challenges, such as replenishing the sample fast enough between X-ray pulses and ensuring high repetition rate detection of the signals produced. This presentation will give an overview of experiments performed to date at the Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX) instrument* that have taken advantage of the high number of pulses and repetition rate provided by the European XFEL and illustrate how some of the key challenges have been addressed. An outlook to future developments and wishes from the user community regarding increased duty cycle operation will also be discussed. * Decking, W. et al. Nat. Photonics 14, 391 (2020) ** Mancuso, A. P. et al. J. Synchrotron Radiat. 26, 660 (2019)
	Slides WE3A1 [1.759 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A2	Beam on Demand for Superconducting Based Free-electron Lasers
	Z. Zhang, Z. Huang SLAC, Menlo Park, California, USA
	The multiplexing capabilities of superconducting-based X-ray free-electron lasers (FELs) have garnered significant attention in recent years. The need for wide-ranging photon properties from multiple undulator lines calls for more flexible beam manipulation techniques. To fully realize the potential of superconducting-based FEL facilities, the concept of "beam on demand" has been introduced, offering tailored beam properties for each undulator line at the desired repetition rate. In this work, we present the efforts made at LCLS-II to enhance its multiplexing capabilities, including (1) development of a normal conducting cavity, known as a chirper, to achieve shot-by-shot control of beam compression; and (2) proposal of a multiplexed configuration for the LCLS-II injector to deliver low-emittance electron beams of varying beam charges at high repetition rates. The implementation of these techniques can significantly enhance the flexibility and improve the performance of the facility.
	Slides WE3A2 [2.268 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A3	Multi-FELOs Driven by a Common Electron Beam	164
	C.-Y. Tsai HUST, Wuhan, People’s Republic of China Y. Zhang JLab, Newport News, Virginia, USA
	Generating an FEL requires a high-brightness electron beam. To produce multiple FELs, the linac beam must be shared to enable one beam driving an undulator. This leads to a reduced average current and compromised FEL performance. Recently, a concept of multiple FELs driven by one electron beam was proposed, which enables reduction of equipment and improvement of productivity. We present here a simulation study based on an extended 1D FEL oscillator model to demonstrate this concept. The system consists of two FEL oscillators arranged side-by-side and one electron beam passing through them. As such, the second, downstream oscillator is driven by bunches already been used once, while the first oscillator always receives fresh bunches from the linac. The study shows lasing could be achieved for both oscillators, their radiation intensities at saturation are comparable, thus meet needs of users. The concept also enables a potential application using a circulator ring such that an oscillator can be driven alternately by fresh linac bunches from and used bunches in the circulator ring. Extending the concept to cases of more than two FEL oscillators driven by one beam is also explored.
	Slides WE3A3 [0.540 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE3A3
About •	Received ※ 23 August 2023 — Revised ※ 23 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A4	Energy Recovery Linac Based Multi-pointing Fully Coherent Light Source
	Z. Wang, C. Feng, Z.T. Zhao SARI-CAS, Pudong, Shanghai, People’s Republic of China
	Energy recovery linac (ERL) holds great promise for generating high repetition-rate and high brightness electron beams. In this paper, we consider the combination of ERL with the recently proposed anglerangular-dispersion induced microbunching technique to generate fully coherent radiation pulses with high average brightness and tunable pulse length. Besides, we design a multiplexed emitting system, which consists of multi-bend achromats (MBAs), matching sections and radiators to support multi-beamline operation in the long straight section of the ERL. Theory and simulation have been carried out and the results indicate that the microbunching and beam quality maintains well after four times of bending, indicating the continuously radiation with the wavelength of 13.5 nm and the peak power of 2 MW.
	Slides WE3A4 [4.548 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A5	Development of Multi-alkali Antimonides Photocathodes for High-brightness Photoinjectors
	S.K. Mohanty, M. Krasilnikov, A. Oppelt, F. Stephan DESY Zeuthen, Zeuthen, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany L. Monaco, C. Pagani, D. Sertore INFN/LASA, Segrate (MI), Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	Funding: This work was supported by the European XFEL re-search and development program. Multi-alkali antimonide photocathodes can have high quantum efficiency similar to UV-sensitive (Cs₂Te) photocathodes but with the advantages of photoemission sensitivity in the green wavelength and a significant reduction in the mean transverse energy of photoelectrons. In order to optimize and better understand the photo emissive film properties of K-Cs-Sb photocathodes, a batch of two photocathodes with different thicknesses was grown on molybdenum substrates via a sequential deposition method in a new preparation system at INFN LASA. During the deposition, a "multi-wavelengths" diagnostic, i.e., the measurements of the real-time photocurrent and reflectivity at different wavelengths, has been applied during the photocathode film growth. In addition, in the framework of density functional theory (DFT), we investigated the electronic and optical properties of K{₂}CsSb material. This allowed us to establish a correlation between the calculated and measured optical properties, such as reflectivity. In this report, we present and discuss the experimental results obtained from the two different thickness K{₂}CsSb photocathodes, along with the DFT results of K{₂}CsSb material.
	Slides WE3A5 [4.063 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A6	A High Brightness Travelling-wave C-Band Photogun for a Brightness Upgrade to SwissFEL
	T.G. Lucas PSI, Villigen PSI, Switzerland
	Funding: This project has received funding from the European Unions Horizon 2020 Research and Innovation program under GA No101004730. One of the performance limiting factors of the next generation of XFELs is the generation of high brightness electron bunches. The current generation of S-band RF photoguns have reached their brightness limit. To continue to push brightness boundaries, a new photogun concept is needed. This contribution presents the design of a novel travelling-wave RF photogun that operates in the C-band regime. Beam dynamics simulations of this photogun illustrate that it can achieve a 5D beam brightness five times greater than the SwissFEL standing-wave gun. With the increased beam brightness, it is expected that intrabeam scattering (IBS) will play a more significant role through increasing the sliced energy spread (SES). Calculations of the IBS-induced SES illustrate that the increase in SES does not completely undo the brightness gain. We present the evolution of the SES over the injector and discuss how it influences the concept of optimising the beam brightness of an injector. Finally, this novel design also offers a path forward into higher repetition rate operation through its low attenuation, travelling-wave philosophy. This opens up the possibilities of operation into the kHz regime.
	Slides WE3A6 [2.007 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P09	Heat Load and Radiation Pulse of Corrugated Structure at SHINE Facility	168
	J.J. Guo Zhangjiang Lab, Shanghai, People’s Republic of China H.X. Deng, D. Gu, Q. Gu, M. Meng, Z. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China
	Corrugated structure modules are being proposed for installation after the end of the linac and before the undulator regions of SHINE facility, where it has been used for energy chirp control and as a fast kicker for two color operation of the FEL. When ultra-relativistic bunch of electrons passing through corrugated structure will generate strong wakefield, we find most of the wake power lost by the beam is radiated out to the sides of the corrugated structure in the form of THz waves, and the remaining part casue Joule heating load on the corrugated structure wall. In this paper, we estimate the radiation pulse power and Joule power loss of the corrugated structure in SHINE facility.
	Poster WE4P09 [0.787 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P09
About •	Received ※ 23 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P12	Upgrades of High Level Applications at Shanghai Soft X-Ray FEL Facility	171
	H. Luo, D. Gu, T. Liu, Z. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China K.Q. Zhang SSRF, Shanghai, People’s Republic of China
	The Shanghai soft X-ray free-electron laser(SXFEL) facility has made significant progress in recent years with the rapid, upgraded iterations of the high level software, including but not limited to energy matching, orbit feedback and load, beam optimization, etc. These tools are key components in operation and experiment of free electron laser facility. Some key applications are presented in this paper.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P12
About •	Received ※ 21 August 2023 — Revised ※ 29 August 2023 — Accepted ※ 30 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P13	Physics Design and Beam Dynamics Optimization of the SHINE Accelerator	174
	D. Gu, Z. Wang, M. Zhang SARI-CAS, Pudong, Shanghai, People’s Republic of China
	Shanghai HIgh Repetition Rate X-ray Free Electron Laser and Extreme Light Facility (SHINE) is a hard X-ray FEL facility which is driven by a 1.3 km supercon-ducting Linac, aims to provide high repetition rate pulses up to 1 MHz . In this study, we present the physics design of the SHINE accelerator and considerations of beam dynamics optimizations. Start-to-end simulation results show that, a high brightness electron beam with over 1500 A quasi-flat-top current can be attained which fully meet the requirements of FEL lines. Furthermore, design of the bypass line is also discussed.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P13
About •	Received ※ 23 August 2023 — Revised ※ 30 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P14	Layout of the Undulator-to-dump line at the SHINE	177
	T. Liu, S. Chen, H.X. Deng, B. Liu, Z. Qi SARI-CAS, Pudong, Shanghai, People’s Republic of China Z.F. Gao SSRF, Shanghai, People’s Republic of China N. Huang Zhangjiang Lab, Shanghai, People’s Republic of China
	The Shanghai HIgh repetitioN rate XFEL and Extreme light Facility as the first hard X-ray free-electron laser (FEL) facility in China, is currently under construction in the Zhangjiang area, Shanghai. It aims to deliver X-ray covering photon energy range from 0.4 to 25 keV, with electron beam power up to 800 kW. Downstream of the undulator line, the beam transport design of the undulator-to-dump line is critical which is mainly used for realization of FEL diagnostics based on transverse deflecting structure and beam absorption in the dump. In this manuscript we describe the current layout of this system.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P14
About •	Received ※ 20 August 2023 — Revised ※ 22 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P15	Multichromatic Free-electron Laser Generation Through Frequency-beating in a Chirped Electron Beam	181
	Z. Qi, C. Feng SARI-CAS, Pudong, Shanghai, People’s Republic of China
	We propose a simple method to generate mode-locked multichromatic free-electron laser (FEL) through a longitudinal phase space frequency-beating in a chirped electron beam. Utilizing the two stage modulator-chicane setups in Shanghai Soft X-ray FEL facility, together with a chirped electron beam, we are going to imprint a frequency-beating effect into the electron beam. Hence periodic bunching trains can be formed and can be used to generate mode-locked FEL radiation pulses. Theoretical analysis and numerical simulations are given out to demonstrate the performance of the method. The results indicate that mode-locked FEL in temporal and frequency domain can be formed at the 18th harmonic of the seed laser, with the central wavelength being about 14.58nm and the peak power over 2GW.
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P15
About •	Received ※ 01 September 2023 — Revised ※ 01 September 2023 — Accepted ※ 01 September 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH2A0	Short Free-electron Laser Pulses: The User Perspective
	C. Bostedt PSI, Villigen PSI, Switzerland
	Free-electron laser sources can deliver x-ray pulses with unprecedented intensities. While often the performance of the x-ray laser sources and experimental needs revolve about the achievable pulse energies, the pulse length is an equally or perhaps even more important parameter. Already the first ionization measurements in atomic neon revealed that the x-ray dynamics change fundamentally when the pulse length approaches the femtosecond time scales of inner-shell decay processes [1]. Related, the pulse length was demonstrated to be an important parameter for the electronic response in diffraction experiments [2] and discussed in the broader context of damage processes in femtosecond crystallography [3] and imaging [4]. With the advent of attosecond x-ray pulses, new opportunities opened for non-linear X-ray spectroscopy [5] as well as following coherent electronic processes [6]. In my talk, I will briefly present these various short pulse applications to set the stage for the workshop discussions. [1] Young et al., Nature 466, 7302 (2010) [2] Ferguson et al., Sci. Adv. 2, 1500837 (2016) [3] Nass et al., Nat. Comm. 11, 1814 (2020) [4] Ho et al., Nat. Comm 11, 167 (2020) [5] O¿Neil, PRL 125, 073203 (2020) [6] Li., Science 375, 285 (2022)
	Slides TH2A0 [2.888 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH2A1	Dechirper System for Fresh-slice Applications at the European XFEL
	W. Qin, W. Decking, M.W. Guetg, J.J. Guo, S. Liu, T. Wohlenberg, I. Zagorodnov DESY, Hamburg, Germany E. Gjonaj TEMF, TU Darmstadt, Darmstadt, Germany J.J. Guo SINAP, Shanghai, People’s Republic of China J.J. Guo University of Chinese Academy of Sciences, Beijing, People’s Republic of China
	Fresh-slice lasing using dechirper induced time-dependent orbit oscillation is capable of producing high intensity two-color XFEL pulses and high power short pulses at femtosecond level. At the European XFEL, a dechirper system for fresh-slice applications for both the hard x-ray beamline SASE1 and the soft x-ray SASE3 beamline is being developed. In this contribution, we present the novel design of the wakefield structure and initial commissioning efforts.
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH2A2	Generation of Intense Attosecond Pulses at the European XFEL
	J.W. Yan, G. Geloni, C. Lechner, S. Serkez EuXFEL, Schenefeld, Germany Y. Chen, P. Dijkstal, M.W. Guetg, E. Schneidmiller DESY, Hamburg, Germany
	X-ray free-electron lasers (XFELs) have paved the way for significant advancements in attosecond science by generating intense, ultrashort pulses. We are currently developing AttoSecond Pulses with eSASE and Chirp-Taper schemes (ASPECT) project at the European XFEL, designed to exploit these capabilities. In its initial stages, ASPECT will be used to produce attosecond-long pulses at two out of the three SASE lines at the European XFEL: SASE1 and SASE3, dedicated to producing hard and soft x-rays respectively. In this presentation, we will report design studies and preliminary experimental results at the European XFEL.
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH2A3	Progress on Fresh-slice Multi-stage Amplification at SwissFEL
	G.L. Wang, E. Prat, S. Reiche, K. Schnorr PSI, Villigen PSI, Switzerland
	We present the progress of generating high-power and short FEL pulses using the fresh-slice multi-stage amplification scheme at Athos, the soft X-ray beamline of SwissFEL. We use a transversely tilted electron beam traveling through the unique Athos layout with magnetic chicanes between every two undulator modules. The tail of the bunch produces a short pulse in the first amplification stage. The rest of the electron beam further amplifies the short FEL pulse in up to three additional stages. Our results show the production of FEL radiation with pulse energies of several hundreds of microjoules and pulse durations of about one femtosecond. This operation mode will allow us to advance the scientific opportunities of nonlinear optics and imaging experiments.
	Slides TH2A3 [2.411 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH4A1	Progress Towards X-ray Free-electron Laser Driven by Plasma Wakefield Accelerator at SXFEL
	F. Li, J.F. Hua, W. Lu, Z. Song, H.Y. Xiao TUB, Beijing, People’s Republic of China C. Feng, Z. Wang, Z.T. Zhao SARI-CAS, Pudong, Shanghai, People’s Republic of China T.L. Zhang Tsinghua University, Beijing, People’s Republic of China
	Free-electron lasers (FEL) are unique light source for various applications in structural biology, chemistry and condense physics. Plasma-based accelerators can provide ultrahigh accelerating gradient which is 3~4 orders of magnitude higher than conventional technology, holding the potential for a revolution in particle accelerators. This novel technology therefore has been given high expectations for the development of compact free-electron lasers. SXFEL is a single-pass FEL user facility that provides 2~10 nm radiation for fundamental and applied research. In frame of this report, we present concept and design of a large-bandwidth XFEL based on a plasma wakefield accelerator (PWFA) driven by SXFEL electron beams. An ultrabroad bandwidth is achieved by chirping the electron beam in a hollow-channel plasma and simulations demonstrate that a spectral bandwidth of up to 24% can be obtained in this scheme. We will also present the recent progress on the construction of PWFA-based XFEL experimental station at SXFEL, and the preliminary experimental results on the PWFA and FEL radiation generation.
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH4A2	A Compact Inverse Compton Scattering Source Based on X-band Technology and Cavity-enhanced High Average Power Ultrafast Lasers	257
	A. Latina, R. Corsini, L.A. Dyks, E. Granados, A. Grudiev, V. Mușat, S. Stapnes, P. Wang, W. Wuensch CERN, Meyrin, Switzerland E. Cormier CELIA, Talence, France G. Santarelli ILE, Palaiseau Cedex, France
	A high-pulse-current photoinjector followed by a short high-gradient X-band linac and a Fabry-Pérot enhancement cavity are considered as a driver for a compact Inverse Compton Scattering (ICS) source. Using a high-power ultra-short pulse laser operating in burst mode in a Fabry-Pérot enhancement cavity, we show that outcoming photons with a total flux over 10¹³ and energies in the MeV range are achievable. The resulting high-intensity and high-energy photons allow various applications, including cancer therapy, tomography, and nuclear material detection. A preliminary conceptual design of such a compact ICS source and simulations of the expected performance are presented.
	Slides TH4A2 [2.962 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TH4A2
About •	Received ※ 22 August 2023 — Revised ※ 26 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH4A3	An Active Q-switched X-ray Regenerative Amplifier Free-electron Lasers
	J. Tang, E. Hemsing, Z. Huang, Z. Zhang SLAC, Menlo Park, California, USA
	Despite tremendous progress in X-ray free-electron laser (FEL) science over the last decade, future applications still demand fully coherent, stable X-rays that have not been demonstrated in existing X-ray FEL facilities. In this Letter, we describe an active Q-switched X-ray regenerative amplifier FEL (XRAFEL) to produce fully coherent, high-brightness, hard X-rays. By using simple electron beam phase space manipulation, we show this scheme is very flexible in controlling the X-ray cavity quality factor Q and hence the output radiation. We report both theoretical and numerical studies on this scheme with a wide range of accelerator, X-ray cavity, and undulator parameters
	Slides TH4A3 [1.855 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH4A4	A Proposal for Generating Fully Coherent X-ray FEL with Femtosecond Pulse Based on Fresh-Slice	261
	Z.F. Gao SSRF, Shanghai, People’s Republic of China J.W. Yan EuXFEL, Schenefeld, Germany
	This study aims to propose a new principle for generating fully coherent femtosecond X-ray pulse on the Shanghai soft X-ray Free Electron Laser User Facility (SXFEL-UF), which was based on fresh-slice technique. The electron beam was kicked transversely to get a time-related transverse tilt. The sub-10-femtosecond bunch was achieved first because of the spatiotemporal synchronization effect of the seed laser modulation. Then the FEL pulse duration was even shorter because of harmonic lasing. In the cascaded HGHG mode, the laser generated by the beam tail modulated the beam head in the second stage to reach higher harmonics, while in the EEHG mode, the same part of the electron beam was modulated twice. The influence of emittance and energy chirp of the electron beam on the scheme was analyzed, and the instability caused by transverse position jitter and energy jitter of the chirped beam was evaluated. The relationship between the pulse duration and the transverse deflection of the beam is verified. The scheme is also explored to generate linearly polarized femtosecond pulse at 6 nm and circularly polarized femtosecond pulse at 3 nm simultaneously.
	Slides TH4A4 [3.281 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-FLS2023-TH4A4
About •	Received ※ 21 August 2023 — Revised ※ 24 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FR1M1	Summary Report of Working Group A: Linac-based Light Sources
	E. Prat PSI, Villigen PSI, Switzerland M.W. Guetg DESY, Hamburg, Germany E. Hemsing SLAC, Menlo Park, California, USA T. Inagaki RIKEN SPring-8 Center, Hyogo, Japan
	The paper highlights the key points arising from six insightful and instructive working group sessions.
	Slides FR1M1 [8.156 MB]
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

MO1L3

Production and Characterization of Hard X-rays Beyond 25 keV

Y. Chen, T. Long
DESY, Hamburg, Germany

Dedicated R&D programs, aimed for delivering ultra-hard X-rays beyond 25 keV for advanced user experiments, have been launched at the European XFEL. Characterization of the electron beam and the photon beam transport to the instrumentation have been carried out. Given the very first experiments, optimized SASE intensities of 0.8 mJ at 24.58 keV and 0.3 mJ at 30.24 keV, both lasing at the fundamentals, have been simultaneously demonstrated at two hard X-ray beamlines of the facility. These experiments were carried out using optimized low-emittance electron beams based on existing undulators with a 4 cm period and 16.4 GeV electron beam energy. It has also been shown, that the transport of 30 keV photon beams to the user experiments was made possible. The obtained results will be presented. Further discussions on the realization of ultra-hard X-rays using advanced techniques, as well as improved longitudinal beam diagnostics of the facility will be given in detail.

Slides MO1L3 [8.172 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A1

Progress on SHINE Machine

D. Wang
SINAP, Shanghai, People’s Republic of China

SHINE (Shanghai HIgh repititioN rate hard x-ray free electron laser and Extreme light) is a superconducting linac-based free electron laser facility. It consists of a cw VHF electron gun, 75 8-cavity cryomodules, fast beam distributions, 3 FEL undulator lines as well as the photon beam lines/end-stations. In this talk we will give an introduction to the latest progress of the machine part of this project. Supported by the project funding (including the R&D and construction money that come up at same time) extensive prototyping has been conducted on major components like high rep-rate gun, cavities/cryomodules for cw linac, large cryogenic plant, fast kickers and undulators, among others. The cw beam test facility was set up to operate at cw mode for electron gun and cryomocules.

Slides MO3A1 [11.431 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A2

Status and Perspectives for the Swiss Free-Electron Laser (SwissFEL)

26

T. Schietinger
PSI, Villigen PSI, Switzerland

We summarize the status of SwissFEL, the X-ray free-electron laser at the Paul Scherrer Institute. Apart from some key operational performance figures the presentation covers the state of the experimental stations and their capabilities, gives a few scientific highlights and an overview of the use of special modes beyond SASE at our facility. Furthermore we report on progress of our seeding upgrade program on the soft X-ray line. Lastly we mention our long-term upgrade plans for a third undulator beamline in the tender and hard X-ray regime.

Slides MO3A2 [8.398 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-MO3A2

About •

Received ※ 29 August 2023 — Revised ※ 30 August 2023 — Accepted ※ 30 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A3

Status of the LCLS-II Superconducting Linac

D. Gonnella
SLAC, Menlo Park, California, USA

Funding: US DoE
The LCLS-II project installed a new superconducting linac into the existing SLAC tunnel to enable a high repetition rate x-ray FEL. Over the last 1.5 years, the commissioning of the new linac has taken place and been overall very successful. The status of the commissioning and experience from early operations of the new superconducting linac will be presented.

Slides MO3A3 [5.118 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A4

European XFEL Status Overview

M. Scholz
DESY, Hamburg, Germany

Since its launch in 2017, European XFEL has been operating reliably and stably, delivering photons to user experiments. The range of services, the overall performance and the provision of special operating modes have been continuously improved. Its superconducting accelerator delivers up to 27000 electron bunches per second in a 10 Hz pulsed mode to 3 undulator beamlines, which in turn can deliver photons to one of two associated instruments. The high electron beam energy of up to 17.5 GeV predestines this facility for high photon energies up to 30 keV. In addition to the default delivery modes, the user community is increasingly requesting other modes of operation such as self-seeding, very short pulses, two colours or customised bunch distributions in the individual pulse trains. We will present a brief summary of the current status of the different operating modes and give an outlook into the future.

Slides MO3A4 [11.059 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A5

FLASH: Status and Upgrade

32

M. Vogt, S. Schreiber, J. Zemella
DESY, Hamburg, Germany

FLASH, the Soft X-Ray and Extreme-UV Free Electron Laser at DESY, is undergoing a substantial upgrade and refurbishment project, called FLASH2020+. The project will finally enable external seeded and SASE FEL operation for a wavelength range down to 4 nm with the EEHG method. This is achieved in two long shutdowns from November 2021 to August 2022 and from June 2024 to August 2025. Key ingredient of the upgrade were installation of a laser heater, replacing two early TTF-type L-band SRF accelerating modules by modern, high-gradient XFEL-type modules, redesign of the 2nd bunch compressor, and complete redesign of the FLASH1 beam line for HGHG/EEHG seeding. This talk will report on the project and the status of FLASH after the first shutdown with emphasis on beam dynamics aspects.

Slides MO3A5 [1.108 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-MO3A5

About •

Received ※ 25 August 2023 — Revised ※ 26 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A6

Recent status of PAL-XFEL

M.H. Cho, I. Eom, H. Heo, H.-S. Kang, C.-K. Min, I.H. Nam, J. Park, S.H. Park, C.H. Shim, H. Yang
PAL, Pohang, Republic of Korea

Since opened to users in 2017, significant progress of PAL-XFEL has been made in operations including increasing the FEL pulse energy and the FEL photon energy, generating stable and high power self-seeding FELs, and two-color FELs. In the beamline, new instruments or endstations have been added such as the femtosecond X-ray scattering (FXS) with 800 nm laser pulse, the X-ray absorption spectroscopy (SAX), the serial femtosecond crystallography (SFX) with operation with developed noble sample-delivery-systems, Fourier-Transform Holography (FTH), and so on. Overall, beamline operation has enabled excellent scientific results through efficient user experiments. This talk will introduce recent status of PAL-XFEL and show representative experiment results shortly.

Slides MO3A6 [3.739 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A7

Present Status of SACLA and Plans for Future Upgrades

T. Inagaki, T. Hara, E. Iwai, C. Kondo, H. Maesaka, H. Tanaka
RIKEN SPring-8 Center, Hyogo, Japan

SACLA has two XFEL beamlines, BL3 and BL2, which are driven by an 8-GeV normal-conducting C-band high-gradient accelerator and provide SASE from 4 keV to 20 keV, and an EUV-FEL beamline BL1, which is driven by an 800-MeV accelerator and provides SASE from 40 eV to 150 eV. To perform the parallel operation of BL3 and BL2 and the top-up injection into the SPring-8 storage ring, the electron gun, accelerating RF, focusing magnets, and switchyard magnets are synchronously controlled for each 60 Hz pulse. In recent years, experiments using special FELs such as reflection-type self-seeded FELs, two-color, double-pulsed FELs, ultra-short pulsed FELs and nano-focusing optics have been conducted at XFEL beamlines. In order to supply XFELs tailored to various experimental conditions, an automatic tuning system of the accelerator using machine learning has been established and is used for daily tuning. In the future, we plan to improve and precisely control the characteristics of the FEL, such as intensity, pulse duration, spectrum, photon energy, and pulse repetition rate. To achieve these goals, we are working on 1) refinement of accelerator models using electron beam monitors and machine learning, 2) development of the electron gun to increase the beam brightness, 3) development of the efficient RF acceleration. For the purpose of 3, we have started to study a new normal-conducting accelerator design, with the goal of increasing the pulse repetition rate while maintaining XFEL performance and power consumption, to be consistent with ¿Green Facility¿ declaration. In this presentation, we introduce the status and future plans for upgrading SACLA.

Slides MO3A7 [1.161 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A8

FERMI FEL Upgrade Plans, an Overview

S. Di Mitri, E. Allaria, L. Badano, P. Cinquegrana, I. Cudin, G. D’Auria, M.B. Danailov, G. De Ninno, P. Delgiusto, A.A. Demidovich, D. Garzella, L. Giannessi, C. Masciovecchio, G. Penco, P. Rebernik Ribič, N. Shafqat, P. Sigalotti, C. Spezzani, L. Sturari, M. Trovò
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
G. De Ninno
University of Nova Gorica, Nova Gorica, Slovenia
L. Giannessi
LNF-INFN, Frascati, Italy

Short and long term upgrade plans of the FERMI free-electron laser facility at Elettra Sincrotrone Trieste, Italy, will be reported. They include the ongoing linear accelerator energy upgrade and the conversion of the first undulator line to echo-enabled harmonic generation. The upgrade of the second undulator line to a two stage echo-based fresh-bunch scheme is also under study.

Slides MO3A8 [1.847 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MO3A9

Comissioning Progress and Advanced FEL Experiments at the SXFEL Facility

C. Feng, B. Liu, Z. Wang, Z.T. Zhao
SARI-CAS, Pudong, Shanghai, People’s Republic of China

The Shanghai soft X-ray Free-Electron Laser facility (SXFEL) is the first X-ray FEL facility in China. The construction of the SXFEL facility was finished in 2022. The output photon energy of the SXFEL can cover the whole water window range. Except for the self-amplified spontaneous emission, various seeding technques have also been adopted for improving the performances of the SXFEL. Here we presents an overview of the SXFEL facility, including the layout and design, construction status, commissioning progress and future plans on advanced FEL experiments.

Slides MO3A9 [4.688 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU2A1

Coherent Free-electron Laser Pulses: The User Perspective

G. De Ninno
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Are fully-coherent pulses the Holy Grail for experiments, which aim at taking full advantage of the properties of a free-electron laser (FEL)? What are the strategies to generate and diagnose them at seeded FEL facilities? What are the requirements for experiments based on pulse shaping and coherent control? How goes it for quantum coherence and the possibility to generate FEL pulses with sub-Poissonian statistics? We will talk about all this and more.

Slides TU2A1 [1.584 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU2A2

Single Longitudinal Mode Generation in Slippage-dominated, Tapered-undulator SASE Soft X-ray FEL

70

D.C. Nguyen, M. Dunham, W. Lou, C.E. Mayes, G. Stupakov
xLight, Palo Alto, USA

SASE FELs operating in the soft X-ray region exhibit multiple temporal and spectral spikes with an overall spectral bandwidth of about 1.5 times the FEL rho parameter. While many ideas have been proposed to achieve fully coherent X-ray FELs, only monochromatic seeding, either harmonic seeding* or SASE self-seeding**, has been experimentally demonstrated to narrow the output spectra of soft X-ray FELs. In this paper, we study a different method that relies on the Slippage-dominated Tapered Undulator (STU) SASE concept to produce a single longitudinal mode in a soft X-ray FEL driven by ~10-fs, 16-pC electron bunches. We pre-sent numerical simulation results that demonstrate single-mode generation and narrow-lined spectra without seeding in a STU-SASE FEL at 6.67 nm.
* E. Alaria et al., Nat Photon 7 (2013) 913-918
** D. Ratner et al., PRL 114 (2015) 050801

Slides TU2A2 [1.125 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU2A2

About •

Received ※ 22 August 2023 — Revised ※ 23 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU2A3

Opportunities and Challenges of the Hard X-ray Self-seeding System at the European XFEL

S. Liu, P. Dijkstal, C. Grech, M.W. Guetg, V. Kocharyan, T. Long, N.S. Mirian, W. Qin
DESY, Hamburg, Germany
G. Geloni, N.G. Kujala, C. Lechner, S. Serkez, J.W. Yan
EuXFEL, Schenefeld, Germany

The Hard X-ray Self-seeding system (HXRSS) at the European XFEL provides users with longitudinally coherent X-ray FEL pulses with narrow bandwidth and high spectral density. With this setup we have achieved a maximum spectral density of about 1 mJ/eV at 9 keV. Combined with the MHz repetition rate, it opens up exciting new opportunities in a wide range of scientific fields. However, the increasing user demand and expectations also poses challenges in machine tuning and operation parameter ranges. We will summarize the HXRSS performance we have achieved and the user delivery experiences in the last two years.

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU2A4

A Low-loss 14 m Hard X-ray Bragg-reflecting Cavity, Experiments and Analysis

R.A. Margraf, Z. Huang, R. Robles
Stanford University, Stanford, California, USA
A. Halavanau, Z. Huang, J. Krzywiński, K. Li, J.P. MacArthur, G. Marcus, R. Robles, A. Sakdinawat, T. Sato, Y. Sun, D. Zhu
SLAC, Menlo Park, California, USA
T. Osaka, K. Tamasaku
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
Bragg-reflecting cavities on the 10 s or 100 s of meter scale are a core component of proposed Cavity-Based X-ray Free-Electron Lasers (CBXFELs). While CBXFELs promise improved longitudinal coherence and spectral brightness over single-pass self-amplification of spontaneous radiation (SASE) FELs, construction and alignment of large Bragg-reflecting cavities can be difficult technical challenge. Our collaboration recently demonstrated stable operation of a low-loss 14 m 9.831 keV X-ray cavity of four Bragg-reflecting diamond mirrors*, a significant step towards a CBXFEL-scale cavity. We in-coupled X-rays from the Linac Coherent Light Source (LCLS) into our cavity via a transmission grating, then measured round-trip efficiencies approaching 88%, or >96% when neglecting losses on in-coupling and focusing optics. Additionally, we characterized transverse oscillations in the cavity, demonstrating the effectiveness of our cavity focusing. We will discuss these results, additional new analysis and consider implications for future CBXFEL projects.
* R. Margraf et al., ‘Low-loss Stable Storage of X-ray Free Electron Laser Pulses in a 14 m Rectangular Bragg Cavity’, In Review, preprint, 2023. doi: 10.21203/rs.3.rs-2465216/v1.

Slides TU2A4 [3.245 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P05

Design of the Test Platform for High Current VHF Electron Gun

80

Z.P. Liu, X.D. Li
SINAP, Shanghai, People’s Republic of China
H.X. Deng, Z.G. Jiang
SARI-CAS, Pudong, Shanghai, People’s Republic of China
H.J. Qian
DESY Zeuthen, Zeuthen, Germany
G. Shu
IHEP, Beijing, People’s Republic of China

A high-average-current VHF electron gun operating in the CW mode is under construction at Shanghai Advanced Research Institute, which is the key component of a kW-power-order free electron laser facility. The average current and the frequency of this electron gun is 1-10 mA and 217 MHz, respectively. To validate the performance of this instrument, a test platform has been designed. The R&D of its vacuum and diagnostics are presented in this work.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P05

About •

Received ※ 23 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P06

The Experimental Progress for the Strong Field Terahertz Radiation at Shanghai Soft X-ray Free-electron Laser Facility

83

K.Q. Zhang, C. Feng
SSRF, Shanghai, People’s Republic of China
Y. Kang
SINAP, Shanghai, People’s Republic of China

Strong field Terahertz (THz) light source has been in-creasingly important for many scientific frontiers, while it is still a challenge to obtain THz radiation with high pulse energy at wide-tunable frequency. In this paper, we introduce an accelerator-based strong filed THz light source to obtain coherent THz radiation with high pulse energy and tunable frequency and X-ray pulse at the same time, which adopts a frequency beating laser pulse modulated electron beam. Here, we present the experi-mental progress for the strong filed THz radiation at shanghai soft X-ray free-electron laser (SXFEL) facility and show its simulated radiation performance.

Poster TU4P06 [1.310 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P06

About •

Received ※ 21 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P07

Design of the Beam Distribution System of SHINE

87

S. Chen
SSRF, Shanghai, People’s Republic of China
H.X. Deng, X. Fu, B. Liu
SARI-CAS, Pudong, Shanghai, People’s Republic of China
B.Y. Yan
SINAP, Shanghai, People’s Republic of China

The Shanghai high-repetition-rate XFEL and extreme light facility (SHINE), as the first hard X-ray free electron laser facility in China, is now under construction. CW electron beam with up to 1 MHz bunch repetition rate from a superconducting RF linac is used to feed at least three individual undulator lines that covers a wide photon energy range (0.4 keV ~ 25 keV). In order to maximize the efficiency of the facility, a beam switchyard between the linac and undulator lines is used to enable the simultaneously operation of the three undulator lines. In this work, the schematic design of the beam switchyard for bunch-by-bunch beam separation of CW beam is described, and the current lattice design of the linac-to-undulator deflection branches and the start-to-end tracking simulation results are presented.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P07

About •

Received ※ 22 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P08

Design and Commissioning of the Beam Switchyard for the SXFEL-UF

91

S. Chen, K.Q. Zhang
SSRF, Shanghai, People’s Republic of China
H.X. Deng, C. Feng, B. Liu, T. Liu, Z. Qi, Z.T. Zhao
SARI-CAS, Pudong, Shanghai, People’s Republic of China

As an important measure of improving the efficiency and usability of X-ray free electron laser facilities, parallel operation of multiple undulator lines realized by a beam switchyard has become a standard configuration in the recent built XFEL facilities. SXFEL-UF, the first soft X-ray free electron laser user facility in China, has finished construction and commissioning recently. The electron beams from the linac are separated and delivered alternately to the two parallel undulator beam lines through a beam switchyard. A stable and fast kicker magnet is used to achieve bunch-by-bunch separation. Optics measures are applied to mitigate the impact of various collective effects, such as coherent synchrotron radiation and micro-bunching instability, on the beam quality after passing through the deflection line of the beam switchyard. In this study, the comprehensive physical design of the beam switchyard is described and the latest results of its commissioning process are presented.

Poster TU4P08 [4.643 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P08

About •

Received ※ 23 August 2023 — Revised ※ 30 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P11

Symmetric Compton Scattering: A Way Towards Plasma Heating and Tunable Mono-chromatic Gamma-rays

95

L. Serafini, A. Bacci, I. Drebot, M. Rossetti Conti, S. Samsam
INFN-Milano, Milano, Italy
C. Curatolo
INFN- Sez. di Padova, Padova, Italy
V. Petrillo, A. Puppin
Universita’ degli Studi di Milano & INFN, Milano, Italy

We analyze the transition between Compton Scattering and Inverse Compton Scattering (ICS), characterized by an equal exchange of energy and momentum between the colliding particles (electrons and photons). In this Symmetric Compton Scattering (SCS) regime, the energy-angle correlation of scattered photons is cancelled, and, when the electron recoil is large, monochromaticity is transferred from one colliding beam to the other. Large-recoil SCS or quasi-SCS can be used to design compact intrinsic monochromatic γ-ray sources based on compact linacs, thus avoiding the use of GeV-class electron beams and powerful laser/optical systems as required for ICS sources. At very low recoil and energy collisions (about 10 keV energy range), SCS can be exploited to heat the colliding electron beam, which is scattered with large transverse momenta over the entire solid angle, offering a technique to trap electrons into magnetic bottles for plasma heating.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P11

About •

Received ※ 24 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P12

Injection Into XFELs, a Review of Trends and Challenges

99

C. Davut
UMAN, Manchester, United Kingdom
Ö. Apsimon
Cockcroft Institute, Warrington, Cheshire, United Kingdom
B.L. Militsyn, S.S. Percival
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Funding: Science and Technology Facilities Council, STFC
In this contribution, we review the low-energy electron injectors for existing X-ray Free-Electron Laser (XFEL) facilities focusing on the buncher and booster sections. The technology choices are parallel to the increasing demand for stricter six-dimensional phase space quality. The current capability for beam parameters and future requirements are laid out alongside a discussion on challenges and technological bottlenecks. In light of this review, preliminary results for a high capability injector providing high repetition rate, and continuous wave emission is presented as an option for the UK XFEL.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P12

About •

Received ※ 23 August 2023 — Revised ※ 24 August 2023 — Accepted ※ 30 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P13

An Introduction to the UK XFEL Conceptual Design and Options Analysis

103

D.J. Dunning, D. Angal-Kalinin, J.A. Clarke, J. Henderson, S.L. Mathisen, B.L. Militsyn, M.D. Roper, E.W. Snedden, N. Thompson, D.A. Walsh, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
P. Aden, B.D. Fell
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
D. Angal-Kalinin, J.A. Clarke, D.J. Dunning, J. Henderson, B.L. Militsyn, N. Thompson, P.H. Williams
Cockcroft Institute, Warrington, Cheshire, United Kingdom
J.L. Collier, J.S. Green
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
J.P. Marangos
Imperial College of Science and Technology, Department of Physics, London, United Kingdom

In October 2022, the UK XFEL project entered a new phase to explore how best to deliver the advanced XFEL capabilities identified in the project’s Science Case. This phase includes developing a conceptual design for a unique new machine to fulfil the required capabilities and more. It also examines the possibility of investment opportunities at existing XFELs to deliver the same aims, and a comparison of the various options will be made. The desired next-generation capabilities include transform-limited operation across the entire X-ray range with pulse durations ranging from 100 as to 100 fs; evenly spaced high rep. rate pulses for enhanced data acquisition rates; optimised multi-colour FEL pulse delivery and a full array of synchronised sources (XUV-THz sources, electron beams and high power/high energy lasers). The project also incorporates sustainability as a key criteria. This contribution gives an overview of progress to date and future plans.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P13

About •

Received ※ 23 August 2023 — Revised ※ 25 August 2023 — Accepted ※ 30 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TU4P16

Transverse Optics-based Control of the Microbunching Instability

107

A.D. Brynes, E. Allaria, G. De Ninno, S. Di Mitri, D. Garzella, C. Spezzani
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
G. De Ninno
University of Nova Gorica, Nova Gorica, Slovenia
G. Perosa
Università degli Studi di Trieste, Trieste, Italy
C.-Y. Tsai
HUST, Wuhan, People’s Republic of China

A number of recent experimental and theoretical studies have investigated novel techniques for suppressing the microbunching instability in high-brightness linac-based light sources. This instability has long been studied as one of the causes of reduced longitudinal coherence in these machines, which are commonly suppressed using a laser heater. This contribution presents recent developments concerning the use of an optics-based scheme to mitigate the microbunching instability in the FERMI free-electron laser, paving the way towards reversible beam heating techniques that could improve the performance of future machines.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TU4P16

About •

Received ※ 23 August 2023 — Revised ※ 29 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE1L1

Status and Future of XFEL Source Developments

S. Reiche
PSI, Villigen PSI, Switzerland

Since the first demonstration of the SASE principle in the X-ray regime, there has been an ongoing development on improving and controlling the properties of the generated X-ray FEL pulses. This presentation gives a brief status on these efforts and an outlook of possible improvements in the future.

Slides WE1L1 [4.884 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE1L2

Progress of Cavity-based X-ray Free-electron Lasers

Z. Huang
SLAC, Menlo Park, California, USA

Cavity-based X-ray Free electron lasers (FELs) such as the X-ray regenerative amplifier FEL (XRAFEL)* and the X-ray FEL oscillator (XFELO)** have been proposed to produce temporally coherent and stable hard X-ray pulses, especially for high-repetition rate FEL facilities. An X-ray cavity consisting of Bragg crystals will be used to recirculate the spectrally filtered X-rays for repetitive interactions with an electron bunch train and to generate high-power and narrow-bandwidth radiation. In this talk, we review the scientific motivation and recent progress of Cavity-based X-ray FELs. We discuss cavity designs, optics requirements, outcoupling schemes, and the latest experimental results. Finally, we introduce the ongoing RD projects at LCLS*** and European XFEL**** to prove the concept, as well as several Cavity-based proposals to enhance X-ray FEL’s spectral brightness by another two to three orders of magnitude compared to the state of art.
* Z. Huang and R.D. Ruth, Phys. Rev. Lett. 96, 144801 (2006).
** K.-J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008).
*** K.J. Kim et al., Cavity-based XFEL R&D Project, this workshop.
**** P. Rauer et al., Phys. Rev. Accel. Beams 26, 020701 (2023).

Slides WE1L2 [5.251 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE2A1

Modified Maxwell-Bloch Equations for X-ray Amplified Spontaneous Emission in X-ray Lasers

K.-J. Kim, R.R. Lindberg, J.-W. Park
ANL, Lemont, Illinois, USA

Funding: This work is supported by the U.S. Department of Energy, Office of Science under Contract No. DE-AC02-06CH11357.
Observations of stimulated emission in atomic media pumped by X-ray FELs have shown that X-ray lasers may be possible using the physical process referred to amplified spontaneous emission(ASE). The coherence and stability of an ASE-based X-ray laser can be improved in an X-ray laser oscillator (XLO)* by employing an X-ray cavity as in the X-ray FEL oscillator (XFELO). We present a Hamiltonian-based, 3D theory in paraxial approximation. Assuming factorization of operator products, the ensemble-averaged Heisenberg equations become Maxwell-Bloch equations which provide a correct description of the stimulated emission. The spontaneous emission is accounted for by adding a random noise term to the atomic coherence, which is uniquely determined from the fact that factorization does not apply for products of operators associated with the same atom. Our theory reproduces the results of the previous 1D theory ** and extends it in including the 3D diffraction effects, in including the seed field, and in incorporating the noise in more versatile way***. It provides a sound numerical framework to evaluate an X-ray laser, either in single pass or oscillator configurations.
*A. Halavanau, et al., PNSA 117, 27 (2020).
**A. Benediktovitch, et al., Phys. Rev. A 99, 013839 (2019)
*** J.-W. Park, K.-J. Kim, and R. Lindberg, Phys. Rev. Lett., submitted

Slides WE2A1 [1.179 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE2A2

An Analytical Method for Longitudinal Phase Space Backtracking

N.S. Sudar, Y. Ding
SLAC, Menlo Park, California, USA

Electron beam driven light sources require a longitudinal phase space exhibiting narrow energy spread and high peak current. In linear accelerators this is typically realized by employing multiple stages of bunch compression coupled with various techniques to shape the electron beam chirp. Increases in repetition rate limit many of these manipulations due to the high average beam power. This encourages manipulation of the electron beam properties at the source or low energy area of the accelerator. However, determining the upstream phase space properties that will lead to a particular final phase space proves difficult due to the many free variables of the accelerator and collective effects. Here we present an analytical method for tracking polynomial coefficients describing the final electron beam chirp and current profile backwards to an upstream point in the accelerator. This is written to arbitrary polynomial order and includes analytical expressions for collective effects. The method is applied to the LCLS-II linac, tracking from the undulator entrance back to the injector exit. The example case provided here leads to a 4 kA peak current flat top distribution and 0.1% RMS energy spread at the undulator entrance, representing a significant increase in the LCLS-II beam brightness. Forward tracking in Elegant of the found ideal distribution at the injector exit and accelerator configuration shows good comparison.

Slides WE2A2 [4.564 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE2A3

A Wiggler-based THz Source at LCLS-II and Studies for a 150-m THz Transport Line for Pump-probe Experiments

M. Henstridge, A.S. Fisher, M.C. Hoffmann, Z. Huang
SLAC, Menlo Park, California, USA

Ultrafast THz pulses with energies of several µJ drive exotic non-equilibrium phenomena in complex materials, yet many of the underlying microscopic mechanisms remain unknown. Current strong-field THz sources rely mostly on difference-frequency mixing of near-infrared laser pulses in crystals at few-kHz repetition rates, but the extension of such sources to higher repetition rates suffers from reduced pulse energies and crystal damage. Here, we present a wiggler-based THz scheme capable of delivering 3-30 THz pulses with energies of 100 µJ at the 100 kHz rate supported by LCLS-II. Two time-delayed electron bunches independently drive the wiggler and x-ray undulator to generate precisely synchronized and optimized x-ray and THz pulses for pump-probe experiments. We built a model transport line to address the significant challenge of transporting the THz emission over the minimum 150-m distance necessary to reach the experimental halls. This concept, scaled to 12-m, has been tested with the 28 THz output of a CO₂ laser. Results indicate that the THz emission can be transported over 150-m with an efficiency near 90%. Further testing is underway at 3.5 THz with a quantum-cascade laser.

Slides WE2A3 [1.066 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE2A4

Scaling of Beam Collective Effects with Bunch Charge in the CompactLight Free-electron Laser

S. Di Mitri, G. D’Auria, R.A. Rochow
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
M. Aicheler
HIP, University of Helsinki, Finland
A. Aksoy
Ankara University, Accelerator Technologies Institute, Golbasi, Turkey
D. Alesini, M. Diomede, M. Ferrario, A. Gallo, A. Giribono, J. Scifo, B. Spataro, C. Vaccarezza, A. Vannozzi
LNF-INFN, Frascati, Italy
G. Burt
Lancaster University, Lancaster, United Kingdom
H.M. Castañeda Cortés, J.A. Clarke, D.J. Dunning, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.A. Clarke, D.J. Dunning, N. Thompson
Cockcroft Institute, Warrington, Cheshire, United Kingdom
M. Croia
ENEA Casaccia, Roma, Italy
V.A. Goryashko
Uppsala University, Uppsala, Sweden
A. Latina, X.W. Wu, W. Wuensch
CERN, Meyrin, Switzerland
A. Mostacci
Sapienza University of Rome, Rome, Italy
F. Nguyen
ENEA C.R. Frascati, Frascati (Roma), Italy

The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges in the range 75-300 pC. Space-charge forces in the injector, linac transverse wakefield, and coherent synchrotron radiation in bunch compressors are all taken into account. The study confirms efficient lasing in the soft X-rays regime with pulse energies up to hundreds of microjoules at repetition rates as high as 1 kHz.

Slides WE2A4 [1.777 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A1

High Pulse Rate Experiments at the European X-ray Free-electron Laser

R. Letrun
EuXFEL, Schenefeld, Germany

The rise of superconducting accelerator technology has brought forth an increase in the pulse rate produced by X-ray free-electron lasers (XFELs) by two orders of magnitude*, up to now, with a further increase on the horizon at new and existing facilities. The high pulse rate has opened up new opportunities for the scientific community, not only in terms of the volume of data that can be acquired, but also in the design of experiments that leverage the high pulse rate. However, these advances come with new challenges, such as replenishing the sample fast enough between X-ray pulses and ensuring high repetition rate detection of the signals produced. This presentation will give an overview of experiments performed to date at the Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX) instrument** that have taken advantage of the high number of pulses and repetition rate provided by the European XFEL and illustrate how some of the key challenges have been addressed. An outlook to future developments and wishes from the user community regarding increased duty cycle operation will also be discussed.
* Decking, W. et al. Nat. Photonics 14, 391 (2020)
** Mancuso, A. P. et al. J. Synchrotron Radiat. 26, 660 (2019)

Slides WE3A1 [1.759 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A2

Beam on Demand for Superconducting Based Free-electron Lasers

Z. Zhang, Z. Huang
SLAC, Menlo Park, California, USA

The multiplexing capabilities of superconducting-based X-ray free-electron lasers (FELs) have garnered significant attention in recent years. The need for wide-ranging photon properties from multiple undulator lines calls for more flexible beam manipulation techniques. To fully realize the potential of superconducting-based FEL facilities, the concept of "beam on demand" has been introduced, offering tailored beam properties for each undulator line at the desired repetition rate. In this work, we present the efforts made at LCLS-II to enhance its multiplexing capabilities, including (1) development of a normal conducting cavity, known as a chirper, to achieve shot-by-shot control of beam compression; and (2) proposal of a multiplexed configuration for the LCLS-II injector to deliver low-emittance electron beams of varying beam charges at high repetition rates. The implementation of these techniques can significantly enhance the flexibility and improve the performance of the facility.

Slides WE3A2 [2.268 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A3

Multi-FELOs Driven by a Common Electron Beam

164

C.-Y. Tsai
HUST, Wuhan, People’s Republic of China
Y. Zhang
JLab, Newport News, Virginia, USA

Generating an FEL requires a high-brightness electron beam. To produce multiple FELs, the linac beam must be shared to enable one beam driving an undulator. This leads to a reduced average current and compromised FEL performance. Recently, a concept of multiple FELs driven by one electron beam was proposed, which enables reduction of equipment and improvement of productivity. We present here a simulation study based on an extended 1D FEL oscillator model to demonstrate this concept. The system consists of two FEL oscillators arranged side-by-side and one electron beam passing through them. As such, the second, downstream oscillator is driven by bunches already been used once, while the first oscillator always receives fresh bunches from the linac. The study shows lasing could be achieved for both oscillators, their radiation intensities at saturation are comparable, thus meet needs of users. The concept also enables a potential application using a circulator ring such that an oscillator can be driven alternately by fresh linac bunches from and used bunches in the circulator ring. Extending the concept to cases of more than two FEL oscillators driven by one beam is also explored.

Slides WE3A3 [0.540 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE3A3

About •

Received ※ 23 August 2023 — Revised ※ 23 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A4

Energy Recovery Linac Based Multi-pointing Fully Coherent Light Source

Z. Wang, C. Feng, Z.T. Zhao
SARI-CAS, Pudong, Shanghai, People’s Republic of China

Energy recovery linac (ERL) holds great promise for generating high repetition-rate and high brightness electron beams. In this paper, we consider the combination of ERL with the recently proposed anglerangular-dispersion induced microbunching technique to generate fully coherent radiation pulses with high average brightness and tunable pulse length. Besides, we design a multiplexed emitting system, which consists of multi-bend achromats (MBAs), matching sections and radiators to support multi-beamline operation in the long straight section of the ERL. Theory and simulation have been carried out and the results indicate that the microbunching and beam quality maintains well after four times of bending, indicating the continuously radiation with the wavelength of 13.5 nm and the peak power of 2 MW.

Slides WE3A4 [4.548 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A5

Development of Multi-alkali Antimonides Photocathodes for High-brightness Photoinjectors

S.K. Mohanty, M. Krasilnikov, A. Oppelt, F. Stephan
DESY Zeuthen, Zeuthen, Germany
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
L. Monaco, C. Pagani, D. Sertore
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

Funding: This work was supported by the European XFEL re-search and development program.
Multi-alkali antimonide photocathodes can have high quantum efficiency similar to UV-sensitive (Cs₂Te) photocathodes but with the advantages of photoemission sensitivity in the green wavelength and a significant reduction in the mean transverse energy of photoelectrons. In order to optimize and better understand the photo emissive film properties of K-Cs-Sb photocathodes, a batch of two photocathodes with different thicknesses was grown on molybdenum substrates via a sequential deposition method in a new preparation system at INFN LASA. During the deposition, a "multi-wavelengths" diagnostic, i.e., the measurements of the real-time photocurrent and reflectivity at different wavelengths, has been applied during the photocathode film growth. In addition, in the framework of density functional theory (DFT), we investigated the electronic and optical properties of K{₂}CsSb material. This allowed us to establish a correlation between the calculated and measured optical properties, such as reflectivity. In this report, we present and discuss the experimental results obtained from the two different thickness K{₂}CsSb photocathodes, along with the DFT results of K{₂}CsSb material.

Slides WE3A5 [4.063 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE3A6

A High Brightness Travelling-wave C-Band Photogun for a Brightness Upgrade to SwissFEL

T.G. Lucas
PSI, Villigen PSI, Switzerland

Funding: This project has received funding from the European Unions Horizon 2020 Research and Innovation program under GA No101004730.
One of the performance limiting factors of the next generation of XFELs is the generation of high brightness electron bunches. The current generation of S-band RF photoguns have reached their brightness limit. To continue to push brightness boundaries, a new photogun concept is needed. This contribution presents the design of a novel travelling-wave RF photogun that operates in the C-band regime. Beam dynamics simulations of this photogun illustrate that it can achieve a 5D beam brightness five times greater than the SwissFEL standing-wave gun. With the increased beam brightness, it is expected that intrabeam scattering (IBS) will play a more significant role through increasing the sliced energy spread (SES). Calculations of the IBS-induced SES illustrate that the increase in SES does not completely undo the brightness gain. We present the evolution of the SES over the injector and discuss how it influences the concept of optimising the beam brightness of an injector. Finally, this novel design also offers a path forward into higher repetition rate operation through its low attenuation, travelling-wave philosophy. This opens up the possibilities of operation into the kHz regime.

Slides WE3A6 [2.007 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P09

Heat Load and Radiation Pulse of Corrugated Structure at SHINE Facility

168

J.J. Guo
Zhangjiang Lab, Shanghai, People’s Republic of China
H.X. Deng, D. Gu, Q. Gu, M. Meng, Z. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China

Corrugated structure modules are being proposed for installation after the end of the linac and before the undulator regions of SHINE facility, where it has been used for energy chirp control and as a fast kicker for two color operation of the FEL. When ultra-relativistic bunch of electrons passing through corrugated structure will generate strong wakefield, we find most of the wake power lost by the beam is radiated out to the sides of the corrugated structure in the form of THz waves, and the remaining part casue Joule heating load on the corrugated structure wall. In this paper, we estimate the radiation pulse power and Joule power loss of the corrugated structure in SHINE facility.

Poster WE4P09 [0.787 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P09

About •

Received ※ 23 August 2023 — Revised ※ 28 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P12

Upgrades of High Level Applications at Shanghai Soft X-Ray FEL Facility

171

H. Luo, D. Gu, T. Liu, Z. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China
K.Q. Zhang
SSRF, Shanghai, People’s Republic of China

The Shanghai soft X-ray free-electron laser(SXFEL) facility has made significant progress in recent years with the rapid, upgraded iterations of the high level software, including but not limited to energy matching, orbit feedback and load, beam optimization, etc. These tools are key components in operation and experiment of free electron laser facility. Some key applications are presented in this paper.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P12

About •

Received ※ 21 August 2023 — Revised ※ 29 August 2023 — Accepted ※ 30 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P13

Physics Design and Beam Dynamics Optimization of the SHINE Accelerator

174

D. Gu, Z. Wang, M. Zhang
SARI-CAS, Pudong, Shanghai, People’s Republic of China

Shanghai HIgh Repetition Rate X-ray Free Electron Laser and Extreme Light Facility (SHINE) is a hard X-ray FEL facility which is driven by a 1.3 km supercon-ducting Linac, aims to provide high repetition rate pulses up to 1 MHz . In this study, we present the physics design of the SHINE accelerator and considerations of beam dynamics optimizations. Start-to-end simulation results show that, a high brightness electron beam with over 1500 A quasi-flat-top current can be attained which fully meet the requirements of FEL lines. Furthermore, design of the bypass line is also discussed.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P13

About •

Received ※ 23 August 2023 — Revised ※ 30 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P14

Layout of the Undulator-to-dump line at the SHINE

177

T. Liu, S. Chen, H.X. Deng, B. Liu, Z. Qi
SARI-CAS, Pudong, Shanghai, People’s Republic of China
Z.F. Gao
SSRF, Shanghai, People’s Republic of China
N. Huang
Zhangjiang Lab, Shanghai, People’s Republic of China

The Shanghai HIgh repetitioN rate XFEL and Extreme light Facility as the first hard X-ray free-electron laser (FEL) facility in China, is currently under construction in the Zhangjiang area, Shanghai. It aims to deliver X-ray covering photon energy range from 0.4 to 25 keV, with electron beam power up to 800 kW. Downstream of the undulator line, the beam transport design of the undulator-to-dump line is critical which is mainly used for realization of FEL diagnostics based on transverse deflecting structure and beam absorption in the dump. In this manuscript we describe the current layout of this system.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P14

About •

Received ※ 20 August 2023 — Revised ※ 22 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WE4P15

Multichromatic Free-electron Laser Generation Through Frequency-beating in a Chirped Electron Beam

181

Z. Qi, C. Feng
SARI-CAS, Pudong, Shanghai, People’s Republic of China

We propose a simple method to generate mode-locked multichromatic free-electron laser (FEL) through a longitudinal phase space frequency-beating in a chirped electron beam. Utilizing the two stage modulator-chicane setups in Shanghai Soft X-ray FEL facility, together with a chirped electron beam, we are going to imprint a frequency-beating effect into the electron beam. Hence periodic bunching trains can be formed and can be used to generate mode-locked FEL radiation pulses. Theoretical analysis and numerical simulations are given out to demonstrate the performance of the method. The results indicate that mode-locked FEL in temporal and frequency domain can be formed at the 18th harmonic of the seed laser, with the central wavelength being about 14.58nm and the peak power over 2GW.

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-WE4P15

About •

Received ※ 01 September 2023 — Revised ※ 01 September 2023 — Accepted ※ 01 September 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH2A0

Short Free-electron Laser Pulses: The User Perspective

C. Bostedt
PSI, Villigen PSI, Switzerland

Free-electron laser sources can deliver x-ray pulses with unprecedented intensities. While often the performance of the x-ray laser sources and experimental needs revolve about the achievable pulse energies, the pulse length is an equally or perhaps even more important parameter. Already the first ionization measurements in atomic neon revealed that the x-ray dynamics change fundamentally when the pulse length approaches the femtosecond time scales of inner-shell decay processes [1]. Related, the pulse length was demonstrated to be an important parameter for the electronic response in diffraction experiments [2] and discussed in the broader context of damage processes in femtosecond crystallography [3] and imaging [4]. With the advent of attosecond x-ray pulses, new opportunities opened for non-linear X-ray spectroscopy [5] as well as following coherent electronic processes [6]. In my talk, I will briefly present these various short pulse applications to set the stage for the workshop discussions.
[1] Young et al., Nature 466, 7302 (2010)
[2] Ferguson et al., Sci. Adv. 2, 1500837 (2016)
[3] Nass et al., Nat. Comm. 11, 1814 (2020)
[4] Ho et al., Nat. Comm 11, 167 (2020)
[5] O¿Neil, PRL 125, 073203 (2020)
[6] Li., Science 375, 285 (2022)

Slides TH2A0 [2.888 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH2A1

Dechirper System for Fresh-slice Applications at the European XFEL

W. Qin, W. Decking, M.W. Guetg, J.J. Guo, S. Liu, T. Wohlenberg, I. Zagorodnov
DESY, Hamburg, Germany
E. Gjonaj
TEMF, TU Darmstadt, Darmstadt, Germany
J.J. Guo
SINAP, Shanghai, People’s Republic of China
J.J. Guo
University of Chinese Academy of Sciences, Beijing, People’s Republic of China

Fresh-slice lasing using dechirper induced time-dependent orbit oscillation is capable of producing high intensity two-color XFEL pulses and high power short pulses at femtosecond level. At the European XFEL, a dechirper system for fresh-slice applications for both the hard x-ray beamline SASE1 and the soft x-ray SASE3 beamline is being developed. In this contribution, we present the novel design of the wakefield structure and initial commissioning efforts.

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH2A2

Generation of Intense Attosecond Pulses at the European XFEL

J.W. Yan, G. Geloni, C. Lechner, S. Serkez
EuXFEL, Schenefeld, Germany
Y. Chen, P. Dijkstal, M.W. Guetg, E. Schneidmiller
DESY, Hamburg, Germany

X-ray free-electron lasers (XFELs) have paved the way for significant advancements in attosecond science by generating intense, ultrashort pulses. We are currently developing AttoSecond Pulses with eSASE and Chirp-Taper schemes (ASPECT) project at the European XFEL, designed to exploit these capabilities. In its initial stages, ASPECT will be used to produce attosecond-long pulses at two out of the three SASE lines at the European XFEL: SASE1 and SASE3, dedicated to producing hard and soft x-rays respectively. In this presentation, we will report design studies and preliminary experimental results at the European XFEL.

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH2A3

Progress on Fresh-slice Multi-stage Amplification at SwissFEL

G.L. Wang, E. Prat, S. Reiche, K. Schnorr
PSI, Villigen PSI, Switzerland

We present the progress of generating high-power and short FEL pulses using the fresh-slice multi-stage amplification scheme at Athos, the soft X-ray beamline of SwissFEL. We use a transversely tilted electron beam traveling through the unique Athos layout with magnetic chicanes between every two undulator modules. The tail of the bunch produces a short pulse in the first amplification stage. The rest of the electron beam further amplifies the short FEL pulse in up to three additional stages. Our results show the production of FEL radiation with pulse energies of several hundreds of microjoules and pulse durations of about one femtosecond. This operation mode will allow us to advance the scientific opportunities of nonlinear optics and imaging experiments.

Slides TH2A3 [2.411 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH4A1

Progress Towards X-ray Free-electron Laser Driven by Plasma Wakefield Accelerator at SXFEL

F. Li, J.F. Hua, W. Lu, Z. Song, H.Y. Xiao
TUB, Beijing, People’s Republic of China
C. Feng, Z. Wang, Z.T. Zhao
SARI-CAS, Pudong, Shanghai, People’s Republic of China
T.L. Zhang
Tsinghua University, Beijing, People’s Republic of China

Free-electron lasers (FEL) are unique light source for various applications in structural biology, chemistry and condense physics. Plasma-based accelerators can provide ultrahigh accelerating gradient which is 3~4 orders of magnitude higher than conventional technology, holding the potential for a revolution in particle accelerators. This novel technology therefore has been given high expectations for the development of compact free-electron lasers. SXFEL is a single-pass FEL user facility that provides 2~10 nm radiation for fundamental and applied research. In frame of this report, we present concept and design of a large-bandwidth XFEL based on a plasma wakefield accelerator (PWFA) driven by SXFEL electron beams. An ultrabroad bandwidth is achieved by chirping the electron beam in a hollow-channel plasma and simulations demonstrate that a spectral bandwidth of up to 24% can be obtained in this scheme. We will also present the recent progress on the construction of PWFA-based XFEL experimental station at SXFEL, and the preliminary experimental results on the PWFA and FEL radiation generation.

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH4A2

A Compact Inverse Compton Scattering Source Based on X-band Technology and Cavity-enhanced High Average Power Ultrafast Lasers

257

A. Latina, R. Corsini, L.A. Dyks, E. Granados, A. Grudiev, V. Mușat, S. Stapnes, P. Wang, W. Wuensch
CERN, Meyrin, Switzerland
E. Cormier
CELIA, Talence, France
G. Santarelli
ILE, Palaiseau Cedex, France

A high-pulse-current photoinjector followed by a short high-gradient X-band linac and a Fabry-Pérot enhancement cavity are considered as a driver for a compact Inverse Compton Scattering (ICS) source. Using a high-power ultra-short pulse laser operating in burst mode in a Fabry-Pérot enhancement cavity, we show that outcoming photons with a total flux over 10¹³ and energies in the MeV range are achievable. The resulting high-intensity and high-energy photons allow various applications, including cancer therapy, tomography, and nuclear material detection. A preliminary conceptual design of such a compact ICS source and simulations of the expected performance are presented.

Slides TH4A2 [2.962 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TH4A2

About •

Received ※ 22 August 2023 — Revised ※ 26 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH4A3

An Active Q-switched X-ray Regenerative Amplifier Free-electron Lasers

J. Tang, E. Hemsing, Z. Huang, Z. Zhang
SLAC, Menlo Park, California, USA

Despite tremendous progress in X-ray free-electron laser (FEL) science over the last decade, future applications still demand fully coherent, stable X-rays that have not been demonstrated in existing X-ray FEL facilities. In this Letter, we describe an active Q-switched X-ray regenerative amplifier FEL (XRAFEL) to produce fully coherent, high-brightness, hard X-rays. By using simple electron beam phase space manipulation, we show this scheme is very flexible in controlling the X-ray cavity quality factor Q and hence the output radiation. We report both theoretical and numerical studies on this scheme with a wide range of accelerator, X-ray cavity, and undulator parameters

Slides TH4A3 [1.855 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TH4A4

A Proposal for Generating Fully Coherent X-ray FEL with Femtosecond Pulse Based on Fresh-Slice

261

Z.F. Gao
SSRF, Shanghai, People’s Republic of China
J.W. Yan
EuXFEL, Schenefeld, Germany

This study aims to propose a new principle for generating fully coherent femtosecond X-ray pulse on the Shanghai soft X-ray Free Electron Laser User Facility (SXFEL-UF), which was based on fresh-slice technique. The electron beam was kicked transversely to get a time-related transverse tilt. The sub-10-femtosecond bunch was achieved first because of the spatiotemporal synchronization effect of the seed laser modulation. Then the FEL pulse duration was even shorter because of harmonic lasing. In the cascaded HGHG mode, the laser generated by the beam tail modulated the beam head in the second stage to reach higher harmonics, while in the EEHG mode, the same part of the electron beam was modulated twice. The influence of emittance and energy chirp of the electron beam on the scheme was analyzed, and the instability caused by transverse position jitter and energy jitter of the chirped beam was evaluated. The relationship between the pulse duration and the transverse deflection of the beam is verified. The scheme is also explored to generate linearly polarized femtosecond pulse at 6 nm and circularly polarized femtosecond pulse at 3 nm simultaneously.

Slides TH4A4 [3.281 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-FLS2023-TH4A4

About •

Received ※ 21 August 2023 — Revised ※ 24 August 2023 — Accepted ※ 31 August 2023 — Issued ※ 02 December 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FR1M1

Summary Report of Working Group A: Linac-based Light Sources

E. Prat
PSI, Villigen PSI, Switzerland
M.W. Guetg
DESY, Hamburg, Germany
E. Hemsing
SLAC, Menlo Park, California, USA
T. Inagaki
RIKEN SPring-8 Center, Hyogo, Japan

The paper highlights the key points arising from six insightful and instructive working group sessions.

Slides FR1M1 [8.156 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)