• W.J. Corbett, A.S. Fisher
  SLAC, Menlo Park, California
• W.X. Cheng
  BNL, Upton, Long Island, New York
• W.Y. Mok
  Life Imaging Technology, Palo Alto, California

For top-up injection it is important to understand the time evolution of the incident charge in the transverse and longitudinal coordinate systems. In SPEAR3, the injection system has a vertically-deflecting Lambertson septum with the injected beam entering ~13mm to the inside. The resulting large-amplitude betatron oscillations give rise to rapid filamentation followed by nominal radiation damping and in some cases non-linear x-y coupling. Similarly, in the longitudinal dimension, a mis-match in beam arrival time or energy can result non-linear beam dynamics and damped synchrotron motion. To the next order, any betatron, bunch length or energy spread mismatch will generate damped ‘quadrupole’ oscillations or even higher-order motion. In this paper we report on measurements of injection beam dynamics in the transverse and longitudinal coordinate systems using a fast-gated, image-intensified CCD camera and a Hamamatsu C5680 streak camera, respectively. The injection beam dynamics are shown to contain relatively complicated evolution in the x-y-z beam distributions that change with injection conditions and storage ring lattice configuration.

• J.E. Dusatko, J. Browne, A.S. Fisher, K.D. Kotturi, S.R. Norum, J.J. Olsen
  SLAC, Menlo Park, California

The LCLS Undulator Beam Loss Monitor System is required to detect any loss radiation seen by the FEL undulators. The undulator segments consist of permanent magnets which are very sensitive to radiation damage. The operational goal is to keep demagnetization below 0.01% over the life of the LCLS. The BLM system is designed to help achieve this goal by detecting any loss radiation and indicating a fault condition if the radiation level exceeds a certain threshold. Upon reception of this fault signal, the LCLS Machine Protection System takes appropriate action by either halting or rate limiting the beam. The BLM detector consists of a PMT coupled to a Cherenkov radiator located near the upstream end of each undulator segment. There are 33 BLMs in the system, one per segment. The detectors are read out by a dedicated system that is integrated directly into the LCLS MPS. The BLM readout system provides monitoring of radiation levels, computation of integrated doses, detection of radiation excursions beyond set thresholds, fault reporting and control of BLM system functions. This paper describes the design, construction and operational performance of the BLM readout system.

• J.C. Dooling, W. Berg, B.X. Yang
  ANL, Argonne
• A.S. Fisher, H.-D. Nuhn, M. Santana-Leitner
  SLAC, Menlo Park, California

A large-solid-angle Cherenkov detector beam loss monitor has been built and tested as part of the Linac Coherent Light Source machine protection system (MPS). The MPS is used to protect the undulator magnets from high-energy electron beam loss that can lead to demagnetization. Lost primaries create a shower of secondary electrons that transit through the radiator medium. The radiator consists of an Al-coated plate of high-purity, fused silica, formed into a tuning fork geometry that envelopes the beam pipe preceding each undulator. The radiator transports Cherenkov photons via internal reflection through a tapered neck into a compact photomultiplier tube (PMT). A simple model based on line sources summed across image planes is used to calculate the radiator optical coupling efficiency eta_c as a function of the electron's transverse position. The results are compared for the case of normally incident electrons with a more detailed Monte Carlo random-walk simulation called RIBO. Both analytical and numerical models show eta_c to be relatively uniform over the full range of transverse positions in the radiator and to be a strong function of surface reflectivity.