SLAC, Menlo Park, California
ANL, Argonne
Funding: Work supported by U.S. Department of Energy under Contract Nos. DE-AC02-06CH11357 and DE-AC02-76SF00515.
We present the performance of the cavity beam position monitor (BPM) system for the LCLS undulator. The construction and installation phase of 34 BPMs for the undulator and 2 for the transport line have been completed. The X-band cavity BPM employs a TM010 monopole reference cavity and a TM110 dipole cavity designed to operate at a center frequency of 11.384 GHz. The signal processing electronics features a low-noise single-stage three-channel heterodyne receiver that has selectable gain and a phase locking local oscillator. The approximately 40 MHz IF is digitized by a 120M sample/second four-channel 16-bit digitizer. System requirements include sub-micron position resolution for a single-bunch beam charge of 200 pC. We discuss the system specifications and commissioning results.
SLAC, Menlo Park, California
Funding: Work supported by U.S. Department of Energy under Contract Nos. DE-AC02-06CH11357 and DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) project at SLAC uses a dense 15 GeV electron beam passing through a 131m undulator to generate extremely bright xrays. The project requires electron bunches with a bunch charge of 20pC to 1nC and bunch lengths of 0.020mm (70fs).To measure the beam resolution to 1 micron (rms) for bunch charge > 20 pC in the undulator, a cavity BPM system was chosen. This system can measure the beam position to within a micron. The LCLS Cavity BPM local oscillator subsystem consists of a second order phase-locked loop (PLL) to synchronize with LCLS timing system and injector system. The output of the PLL is distributed to 36 Cavity BPM receivers and 36 high speed digitizers while maintaining good phase noise and low jitter. This paper describes the design of the PLL and how it met the design specifications of 0.1 degree of phase noise at 119MHz and 1 ns of rms jitter.