Improvement in the beam lifetime by means of an rf phase modulation at the KEK Photon Factory storage ring

Abstract

In the 2.5-GeV Photon Factory storage ring at KEK, we have found that the beam lifetime can be improved by modulating the phase of an rf accelerating voltage at a frequency of 2 times the synchrotron oscillation frequency. By applying this phase modulation with a peak-to-peak amplitude of 3.2\ifmmode^\circ\else\textdegree\fi{}, the beam lifetime could be improved, typically, from 22 to 36 h under a beam current of about 360 mA. At the same time, the longitudinal coupled-bunch instability could be considerably suppressed. The improvement in the beam lifetime can be explained as an improved Touschek lifetime, which was caused by a quadrupole-mode longitudinal oscillation of the stored bunches.