The Particle
Beam Physics Lab (PBPL) at UCLA is developing a single-shot relative
bunch length monitor system for the Linac Coherent Light Source (LCLS)
X-ray Free Electron Laser at SLAC. To ensure high-quality lasing, feedback
systems are needed. The bunch length monitor system will be a crucial
part of the linac longitudinal feedback system, which is necessary to
keep the final peak beam current stable. The system will consist of
two multi-channel single-shot grating polychromators, one after each
bunch compressor, and will use the coherent synchrotron radiation (CSR)
or coherent edge radiation (CER) from bunch compressor chicane dipole
magnets. Details of the system will be presented, and the system will
be compared to alternatives. Plans for testing and integration into
the LCLS beamline will be presented as well.