Bunch Length Measurement by Using a 2-Cell Superconducting RF Cavity in cERL Injector at KEK

Abstract

The development of future light source and linear collider require high quality electron beams with short bunch length. In general, the bunch length was measured by using deflecting cavity which has the time dependent transverse electromagnetic field. It is shown that the transverse electric field of 2-cell superconducting RF (SRF) cavity can also provide the correlation between the bunch length and beam size as like the role of the deflecting cavity in bunch length measurement. The deflection strength was calibrated by changing the RF phase and the beam offset because the strength of transverse electric field of RF cavity depends on the phase of RF field and the beam offset in the cavity. We will present new way to measure the bunch length by using 2-cell SRF cavity, which has the acceleration field of 7.21 MV/m, and the measured result with the bunch length of 3.3 ps (rms) in cERL injector.