Modifying CERN SPS cavities and amplifiers for use in RHIC

A system of ten RF cavities operating at 197 MHz will provide longitudinal focusing during beam storage in the Relativistic Heavy Ion Collider (RHIC). The cavities and tetrode amplifiers are from CERN where they had been used in the Super Proton Synchrotron to accelerate leptons for injection into LEP. The amplifier-cavity system had an impedance pole about 3 MHz below cavity resonance which was a possible source of oscillation with RF feedback. This was not a problem at CERN because the cavities were operated without feedback. The impedance pole was moved lower in frequency by extending the length of the drive line. When this was done it was no longer possible to tune the amplifier to give a good match to the drive loop resulting in about 50% anode efficiency. In the class of operation we are using, an efficiency of 65%-70% is expected. A good match was achieved by increasing the loop coupling from 16Ω to 19Ω