Author: Griesmayer, E.
Paper Title Page
THPRB102 Monte Carlo Optimization of Fast Beam Loss Monitors for LCLS-II 4066
  • M. Santana-Leitner, C.I. Clarke, A.S. Fisher, A.M. Harris, C. Hast, T.T. Liang
    SLAC, Menlo Park, California, USA
  • E. Griesmayer
    CIVIDEC Instrumentation, Wien, Austria
  Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515
Commissioning of the LCLS-II hard X-ray FEL is starting at SLAC National Accelerator Laboratory. This facility will ultimately accelerate electrons to 8 GeV, with beams of 375 kW at 1 MHz. At such high-powers, errant beams will need to be detected very fast -200 μs- to limit exposure and to protect beam-line and safety components. Currently, LCLS-I uses ion chambers both as Point Beam Loss Monitors (PBLM) by collimators, dumps, septa, etc., and also as Long Beam Loss Monitors (LBML) that provide detection coverage in extended areas where the accelerator enclosure is not sufficiently thick to shield full beam losses. But due to the finite ion mobility and related screening effects, ion chambers are not fast enough, and their response would not be linear at high charge rates. LCLS-II will use synthetic mono-crystalline diamond chips as PBLMs, as those offer nanosecond time resolution due to the high mobility of holes generated in the valence band by charged particles. LBLMs will be 200 m-long optical fibers, with photomultipliers to detect Cerenkov photons produced by charged particles in the fibers. Use of these technologies requires tests and models to correlate their response to different beam losses. Response functions for these detectors have been developed for the FLUKA Monte Carlo code. After benchmarking the models, these have been applied to place PBLMs at locations where signal is relatively insensitive to beam-strike uncertainties and sufficiently above electronic noise, while keeping lifetime to radiation-damage long. Also, topologies where found were one PBLM can protect several components, resulting in cost reductions. As for LBLMs, the existing model helps scale signals for different beam loss configurations as a function of the fiber position.
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About • paper received ※ 14 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019  
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