RF frequency shift during beam storage in the SLC damping rings

A method to reduce the horizontal damping time and equilibrium emittance of the SLC damping rings required changing the RF frequency during the beam storage time. The changed frequency causes the beam to pass off center through the quadrupoles effectively stretching the ring. The timing and phasing of the ring is required to be locked to the accelerator for both injection and extraction. The requirement was to change the RF frequency by up to 100 kHz after injection transients were damped. Before extraction from the ring, the bunch had to be in the correct bucket and phase locked to the linac. It was necessary that the frequency shift not interfere with the operation of several feedback loops and that any stimulated bunch oscillations be damped to less than 0.1° at 714 MHz before extraction, less than 200 μs after returning to the nominal frequency of 714.000 MHz. Several methods were evaluated to perform the task. The modifications made to the ring´s RF system and operating parameters to accomplish the intrastore frequency shift are described