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 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*10/sup 12 / 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. (3 refs).