Stochastic cooling in the CERN ISR during pp colliding beam physics
When the ISR is used as a pp collider a high-intensity proton beam in R1 collides with a low-intensity antiproton beam in R2 for periods of up to two weeks. The luminosity lifetime is increased with a vertical stochastic cooling system in R1 designed for currents up to 10 A with a total bandwidth of 3.3 GHz. Cooling rates up to 0.7%/h have been obtained. The R2 antiprotons are cooled vertically with a 100-600 MHz system which decreases the initial beam height by up to a factor 7 and increases the luminosity by a factor 1.3-1.4. A momentum cooling system in R2 (frequency range: 55-155 MHz) creates empty space within the p stacking aperture. This allows several stacks from the antiproton accumulator (AA) to be stored in the ISR. With this system which uses the Palmer method it has been proved experimentally that momentum cooling and horizontal betatron cooling are obtained simultaneously if the betatron phase between pick-up and exciter is an odd number of half-betatron wavelengths. The cooling rate of the momentum cooling system which is power-limited is typically 4%/h at 26 GeV/c. The layout of the cooling systems is shown schematically in Fig. 1. The position of the various elements is mainly determined by the available free space and the lattice parameters. Future applications include vertical cooling of α-particles and cooling of antiprotons in all three planes in an experiment where a circulating 3.5-7.5 GeV/c p beam collides with a hydrogen gas jet target.