Author: Doolittle, L.R.
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WEPAL039 LCLS-II Gun/Buncher LLRF System Design 2258
 
  • G. Huang, K.S. Campbell, L.R. Doolittle, J.A. Jones, Q. Qiang, C. Serrano
    LBNL, Berkeley, California, USA
  • S. Babel, A.L. Benwell, M. Boyes, G.W. Brown, D. Cha, J.H. De Long, J.A. Diaz Cruz, B. Hong, A. McCollough, A. Ratti, C.H. Rivetta, D. Rogind, F. Zhou
    SLAC, Menlo Park, California, USA
  • R. Bachimanchi, C. Hovater, D.J. Seidman
    JLab, Newport News, Virginia, USA
  • B.E. Chase, E. Cullerton, J. Einstein-Curtis, D.W. Klepec
    Fermilab, Batavia, Illinois, USA
  • J.A. Diaz Cruz
    CSU, Fort Collins, Colorado, USA
 
  Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract n. DE-AC02-05CH11231.
For a free electron laser, the stability of injector is critical to the final electron beam parameters, e.g., beam energy, beam arrival time, and eventually it determines the photon quality. The LCLS-II project's injector contains a VHF copper cavity as the gun and a two-cell L-band copper cavity as its buncher. The cavity designs are inherited from the APEX design, but requires more field stability than demonstrated in APEX operation. The gun LLRF system design uses a connectorized RF front end and low noise digitizer, together with the same general purpose FPGA carrier board used in the LCLS-II SRF LLRF system. The buncher LLRF system directly adopts the SRF LLRF chassis design, but programs the controller to run the normal conducting cavities. In this paper, we describe the gun/buncher LLRF system design, including the hardware design, the firmware design and bench test.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL039  
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WEPAL040 High Precision Synchronization Development for HiRES, the Ultrafast Electron Diffraction Beamline at LBNL 2262
 
  • Y. Yang, K.M. Baptiste, M. Betz, L.R. Doolittle, Q. Du, D. Filippetto, G. Huang, F. Ji
    LBNL, Berkeley, California, USA
 
  Precise synchronization between the laser and electron is critical for the pump-probe experiments in the HiRES Ultrafast Electron Diffraction facility. We are upgrading the LLRF and laser control system, which ultimately aims at a synchronization below 50 fs RMS between the pump laser pulse and electron probe at the sample plane. Such target poses tight requirements on the RF field stability both in amplitude and phase, and on the synchronization between the RF field and the laser repetition rate. We are presently developing a new LLRF system that has the potential to decrease the overall noise, reaching the required stability of tens of ppm on RF amplitude and phase. For the laser control side, we are replacing the long coaxial cables with fibers for both control signal transmission and laser signal reception. The control transmission side has been implemented, and the timing jitter has been reduced.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL040  
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WEPAL041 FPGA Based Optical Phase Control for Coherent Laser Pulse Stacking 2265
 
  • Y. Yang, L.R. Doolittle, Q. Du, G. Huang, W. Leemans, R.B. Wilcox, T. Zhou
    LBNL, Berkeley, California, USA
  • A. Galvanauskas
    University of Michigan, Ann Arbor, Michigan, USA
 
  Coherent temporal pulse stacking combines the energy from a train of pulses into one pulse through a series of optical cavities. To stabilize the output energy, the cavity roundtrip phases must be precisely locked to particular values. Leveraging the LLRF expertise we have for conventional accelerators, a FPGA-based control system has been developed for optical cavity phase control. A phase measurement method, ''Modulated Impulse Response'', has been developed and implemented on FPGA. An experiment demonstrated that it can measure and lock the optical phases of four stacking cavities, leading to combination of 25 pulses into one pulse with 1.5 % RMS stability over 30 hours.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL041  
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WEPML007 Active Microphonics Compensation for LCLS-II 2687
 
  • J.P. Holzbauer, B.E. Chase, J. Einstein-Curtis, Y.M. Pischalnikov, W. Schappert
    Fermilab, Batavia, Illinois, USA
  • L.R. Doolittle, C. Serrano
    LBNL, Berkeley, California, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Testing of early LCLS-II cryomodules showed microphonics-induced detuning levels well above specification. As part of a risk-mitigation effort, a collaboration was formed between SLAC, LBNL, and Fermilab to develop and implement active microphonics compensation into the LCLS-II LLRF system. Compensation was first demonstrated using a Fermilab FPGA-based development system compensating on single cavities, then with the LCLS-II LLRF system on single and multiple cavities simultaneously. The primary technique used for this effort is a bank of narrowband filter set using the piezo-to-detuning transfer function. Compensation automation, optimization, and stability studies were done. Details of the techniques used, firmware/software implementation, and results of these studies will be presented.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML007  
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THYGBE3 RF Controls for High-Q Cavities for the LCLS-II 2929
 
  • C. Serrano, K.S. Campbell, L.R. Doolittle, G. Huang, A. Ratti
    LBNL, Berkeley, California, USA
  • R. Bachimanchi, C. Hovater
    JLab, Newport News, Virginia, USA
  • A.L. Benwell, M. Boyes, G.W. Brown, D. Cha, G. Dalit, J.A. Diaz Cruz, J. Jones, R.S. Kelly, A. McCollough
    SLAC, Menlo Park, California, USA
  • B.E. Chase, E. Cullerton, J. Einstein-Curtis, J.P. Holzbauer, D.W. Klepec, Y.M. Pischalnikov, W. Schappert
    Fermilab, Batavia, Illinois, USA
  • L.R. Dalesio, M.A. Davidsaver
    Osprey DCS LLC, Ocean City, USA
 
  Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract n. DE-AC02-76SF00515.
The SLAC National Accelerator Laboratory is building LCLS-II, a new 4 GeV CW superconducting (SCRF) Linac as a major upgrade of the existing LCLS. The LCLS-II Low-Level Radio Frequency (LLRF) collaboration is a multi-lab effort within the Department of Energy (DOE) accelerator complex. The necessity of high longitudinal beam stability of LCLS-II imposes tight amplitude and phase stability requirements on the LLRF system (up to 0.01% in amplitude and 0.01° in phase RMS). This is the first time such requirements are expected of superconducting cavities operating in continuous-wave (CW) mode. Initial measurements on the Cryomodule test stands at partner labs have shown that the early production units are able to meet the extrapolated hardware requirements to achieve such levels of performance. A large effort is currently underway for system integration, Experimental Physics and Industrial Control System (EPICS) controls, transfer of knowledge from the partner labs to SLAC and the production and testing of 76 racks of LLRF equipment.
 
slides icon Slides THYGBE3 [14.389 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THYGBE3  
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THPML099 Phase Extraction and Stabilization for Coherent Pulse Stacking 4895
SUSPL060   use link to see paper's listing under its alternate paper code  
 
  • Y.L. Xu, W.-H. Huang, C.-X. Tang, L.X. Yan
    TUB, Beijing, People's Republic of China
  • L.R. Doolittle, Q. Du, G. Huang, W. Leemans, D. Li, R.B. Wilcox, Y. Yang, T. Zhou
    LBNL, Berkeley, California, USA
  • A. Galvanauskas
    University of Michigan, Ann Arbor, Michigan, USA
 
  Funding: This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Contract DE-AC02-05CH11231.
Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy and high average power. We model the CPS as a digital filter in the Z domain, and implement two deterministic algorithms extracting the cavity phase from limited data where only the pulse intensity is available. In a 2-stage 15-pulse CPS system, each optical cavity is stabilized at an individually-prescribed round-trip phase with 0.7 deg and 2.1 deg RMS phase errors for Stage 1 and Stage 2 respectively. Optical cavity phase control with nm accuracy ensures 1.2% intensity stability of the stacked pulse over 12 hours.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML099  
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