Low level RF control for the LANSCE Proton Storage Ring buncher

The Los Alamos Neutron Science Center (LANSCE) has upgraded the Proton Storage Ring (PSR) for the Short Pulse Spallation Source (SPSS) [1]. 100 microamperes of average beam current is now delivered to the new target assembly. One major task of the improvement project was the design and construction of a power amplifier to increase the drive voltage to the cathode follower final power amplifier used to overcome longitudinal space charge forces in the accumulated beam. With this amplifier and power supply improvements, the buncher voltage from the 2.8 MHz radio frequency system was raised 50% to the present 18 kilovolts (kV) peak. Improvements to the low level RF controls were incorporated, in both the amplitude feedback control and a new phase controller. These systems and the resulting RF performance improvements will be discussed. The upgraded RF buncher has delivered the required performance at LANSCE to ensure that the 100 microampere beam on target was achieved