SLAC, Menlo Park, California
ANL, Argonne, Illinois
We present the performance of the cavity beam position monitor (BPM) system for the Linac Coherent Light Source (LCLS) undulator at SLAC. The construction and installation phase of 36 BPMs have been completed. Commissioning is underway. The X-band cavity BPM employs a TM010 monopole reference cavity and a TM110 dipole cavity designed to operate at nominal 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 phase locking local oscillator. The approximately 40MHz intermediate frequency is digitized to 16 bits at a 119 MHz sampling rate then reduced to baseband digitally. Phase and charge are normalized with respect to the reference cavities. System requirements include sub-micron position resolution for a single-bunch beam charge of 200 pC. Early commissioning results indicate single-bunch resolutions better than 500 nm rms and stabilities better than 1 micron drift over 24 hours.
