High-resolution bunch-length monitor capable of measuring an rms value of a few mm

A bunch-length monitor based on detecting the beam spectrum is presented. The monitor comprises a stripline electrode and a heterodyne detector with a switch. The detailed performance of the monitor was examined on a bench as well as with a beam of the TRISTAN main ring. Calibration was carried out at a low beam current. The measured bunch lengths agree well with the calculated values. It has been demonstrated that the monitor can measure an rms bunch length of 3 mm. The repeatability of the measurement was within ±0.2 mm when the bunch length was 5.7 mm.