Compensation of beam loading in the ISR rf cavities

The rf cavities employed for stacking in the ISR are equipped with a powerful feedback system, which compensates for most of the beam-induced voltage. This system is, however, limited - mainly by the current in the final amplifier tube - to injected beam intensities of about 5 x 1012 protons at most. Higher intensities are now available from the PS. Additional beam-load compensation has, therefore, been added to the existing cavities and feedback amplifiers. This beam-load compensation consists of a pick-up, a one-turn delay cable, a wide-band amplifier chain and a final amplifier, directly connected to the accelerating gap. This system injects into the cavity a current approximately equal and opposite to the beam current