WE2A —  Working Group A: Linac-based Light Sources   (30-Aug-23   11:00—12:30)
Chair: T. Inagaki, RIKEN SPring-8 Center, Hyogo, Japan
Paper Title Page
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 icon Slides WE2A1 [1.179 MB]  
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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 icon Slides WE2A2 [4.564 MB]  
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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 icon Slides WE2A3 [1.066 MB]  
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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 icon Slides WE2A4 [1.777 MB]  
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