Hysteresis Phenomena at the Bunch Lengthening Process in the Accumulation Ring

Abstract

The bunch length was measured using a real-time bunch-length monitor based on the beam spectrum in the accumulation ring. Hysteresis phenomena were observed in the bunch lengthening. That is, two bunch lengths existed depending on changing the direction of the beam current. A longitudinal instability of a bunch was calculated using calculated wake potential by a computer code based on a linearized Vlasov equation. The growth rate was calculated as a function of the energy spread at a fixed beam intensity. It was found that the growth rate did not decay monotonously, but had an unstable peak after decaying to a stable minimum value as the energy spread increased. There are two stable regions of the energy spread on both sides of the peak, suggesting the hysteresis.