LONGITUDINAL BEAM-TRANSFER-FUNCTION MEASUREMENTS AT THE SLC DAMPING RINGS

A longitudinal single-bunch instability[1] in the damping rings at the Stanford Linear Collider (SLC) is thought to contribute to pulse-to-pulse orbit variations in downstream accelerator sections. To better understand this instability, we measured the beam phase and bunch length under har-monic modulations of the rf phase and rf voltage. For small phase-modulations the measured response can be ex-plained by interaction of the beam with the cavity funda-mental mode. For larger excitations, we observed bifurca-tion and hysteresis effects. The response to an rf voltage modulation revealed two peaks near the quadrupole-mode frequency, one of which appears to be related to the longitu-dinal instability. In this paper we present the experimental results.