Author: Jacobson, B.T.
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TUAO02 Beam-Loss Detection for LCLS-II 230
  • A.S. Fisher, C.I. Clarke, B.T. Jacobson, R.A. Kadyrov, E. Rodriguez, L. Sapozhnikov, J.J. Welch
    SLAC, Menlo Park, California, USA
  SLAC is now installing LCLS-II, a superconducting electron linac driven by continuous RF at 1.3 GHz. The 4-GeV, 120-kW beam has a maximum rate of nearly 1 MHz and can be switched pulse-by-pulse to either of two undulators, to generate hard and soft x rays. Two detector types measure beam losses. Point beam-loss monitors (PBLMs) set limits at critical loss points: septa, beam stoppers and dumps, halo collimators, protection collimators (which normally receive no loss), and zones with weak shielding. PBLMs are generally single-crystal diamond detectors, except at the gun, where a scintillator on a PMT is more sensitive to the low-energy (1 MeV) beam. Long beam-loss monitors (LBLMs) use 200-m lengths of radiation-hard optical fiber, each coupled to a PMT, to capture Cherenkov light from loss showers. LBLMs protect the entire 4-km path from gun to beam dump and locate loss points. In most regions two fibers provide redundancy and view the beam from different angles. Loss signals are integrated with a 500-ms time constant and compared to a threshold; if exceeded, the beam is stopped within 0.2 ms. We report on our extensive tests of the detectors and the front-end signal processing.  
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About • paper received ※ 03 September 2019       paper accepted ※ 07 September 2019       issue date ※ 10 November 2019  
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Transverse Profile Diagnostic for High Intensity Beams Using Gas-ionization Characterization  
  • G. Andonian, T.J. Campese, M. Ruelas
    RadiaBeam, Marina del Rey, California, USA
  • B.T. Jacobson
    SLAC, Menlo Park, California, USA
  • C.P. Welsch
    The University of Liverpool, Liverpool, United Kingdom
  High intensity electron beam operations require robust methods to monitor the transverse charge profile at focal points along the transport, in a single-shot and real time mode. In this paper, we describe a technique to characterize the transverse beam distribution using a monitor that images the ionization products of the beam interaction with a molecular beam of neutral gas. The gas sheet monitor concept has been successfully tested for other beam applications and is analogous to solid-target viewscreens. A supersonic gas jet, with localized densities in the 1011-1013 cm-3 range, is generated with a nozzle and an array of skimmers along with differential pumping throughout. The flattened and shaped jet acts similar to a traditional solid-target viewscreen. The beam ionizes the portion of the gas jet it encounters, imprinting the transverse beam profile on the ionization distribution. An electrostatic electrode column extracts the ions and images them onto a two-dimensional detector, such as a micro-channel plate and camera. Here, we describe the design of the gas sheet generator and the ion-column subsystems for SLAC FACET-II beam parameters.  
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