Commissioning the Upgraded Rf Buncher at the Lansce Proton Storage Ring

The 2.8 Megahertz (MHz) cathode-follower RF amplifier system and ferrite-loaded gap assembly for the Proton Storage Ring (PSR) were improved as part of the Los Alamos Neutron Science Center (LANSCE) upgrade for a Short Pulse Spallation Source (SPSS) [1]. The commissioning of PSR commenced in July of 1998. The performance of the cathode-follower amplifier system and gap was measured with as much as five microcoulombs (μC) of circulating beam, approximately forty Amperes of peak current before extraction. The output impedance of the cathode follower was estimated to be approximately eleven Ohms. This was calculated from beam-induced voltage on the gap with the amplifier operating class A (full conduction of plate current), with RF drive off. Measurements showed the perturbation of the gap voltage with beam loading to be minimal. The improved RF system handled the beam loading well. A new phase feedback control system corrected for three degrees of phase shift from unloaded to fully loaded beam conditions, with 18 kV of peak RF voltage across the gap. The amplitude feedback controller made 300 volts of correction for droop, also minimal because of the low output impedance at the gap. Beam instability at PSR with higher current was controlled, as expected, with higher voltage [2]. Analysis of these and other measurements are presented.