WE3A —  Working Group A: Linac-based Light Sources   (30-Aug-23   14:00—16:00)
Chair: E. Hemsing, SLAC, Menlo Park, California, USA
Paper Title Page
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 icon Slides WE3A1 [1.759 MB]  
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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 icon Slides WE3A2 [2.268 MB]  
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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 icon 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
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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 icon Slides WE3A4 [4.548 MB]  
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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 icon Slides WE3A5 [4.063 MB]  
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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 icon Slides WE3A6 [2.007 MB]  
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