Author: Huang, Z.
Paper Title Page
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. 		 
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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 icon Slides WE1L2 [5.251 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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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.  
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TH1D3
 SCU Development at the LCLS for Future FELs  
 
  • P. Krejcik, G.J. Bouchard, G.L. Gassner, Z. Huang, E.M. Kraft, B. Lam, M.A. Montironi, C.D. Nantista, D.C. Nguyen, H.-D. Nuhn, Z.R. Wolf, Z. Zhang
    SLAC, Menlo Park, California, USA
  • J.M. Byrd, J.D. Fuerst, E. Gluskin, Y. Ivanyushenkov, M. Kasa, M.F. Qian, Y. Shiroyanagi
    ANL, Lemont, Illinois, USA
  • X. Permanyer
    ESS, Lund, Sweden
  
  A joint SLAC/ANL development program is underway at the LCLS to demonstrate the advantages of SCUs for FEL beamlines. SCUs offer significant advantages for future FEL beam lines in gain length, wavelength reach, and tunability. The program leverages the storage ring SCUs developed at ANL and addresses the issues of integration in FELs and attaining the necessary micron precision for BBA. Our new modular cryomodule design is extendable to a full-length FEL and integrates the additional FEL components such as the phase shifter, quadrupole and RFBPM into the cold mass to achieve a high packing fraction and minimize the average gain length. Initially, 2 such cryomodules will be installed as afterburners at the end of the existing hard x-ray FEL beam line at the LCLS in order to measure the gain length and validate the beam based alignment procedure based on precision motion control of the cold mass internal to the cryomodule. We report on the status of the testing of these critical components on our precision alignment test stand, and discuss future plans for multiple FEL beamlines to be housed in a single cryomodule as part of the future LCLS expansion program for more user stations.  
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TH3D4
 DFCSR: A Fast Calculation of 2D/3D Coherent Synchrotron Radiation in Relativistic Beams  
 
  • J. Tang, Z. Huang, G. Stupakov
    SLAC, Menlo Park, California, USA
  
  Coherent Synchrotron Radiation (CSR) is regarded as one of the most important reasons that limits beam brightness in modern accelerators. Current numerical packages containing CSR wake fields generally use 1D models, which can become invalid in electron beams with very high brightness. On the other hand, the existing 2D or 3D codes are often slow. Here we report DFCSR, a novel particle tracking code that can simulate 2D/3D CSR and space charge wakes in relativistic electron beams 2 or 3 orders of magnitude faster than conventional models like CSRtrack. We performed benchmark simulations based on FACET-II beams, where electron beams are compressed to reach 300 kA peak current. The tracking code is written in Python and C programming languages with human-friendly input styles and is open-sourced on GitHub. It can serve as a powerful simulation tool for the design of next-generation accelerators.  
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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 icon Slides TH4A3 [1.855 MB]  
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