Compensation of the resistive and reactive transverse wall impedance in the ISR with a feedback system

The transverse coupling impedance has been measured in the ISR in the vertical plane and found to be mostly inductive with a phase angle of about 50 degrees for the lowest mode. The resistive part of this impedance is compensated below 1 MHz by a transverse feedback system. However, by applying to the kicker the signals from two pick-ups giving respectively a resistive and an inductive compensation, the phase angle of the feedback can be varied. The signal levels from the two pick-ups are individually adjusted with the correct settings obtained from the information given by the beam transfer function. In this way the stability margin is increased without changing the electronic gain of the feedback. A special set-up has been developed for the measurement of beam transfer functions at low frequencies (10 kHz to 1 MHz). (0 refs).