Report on the ISR

During 1974, the period covered by this report, the ISR were in operation for 3500 h, of which 80% were for physics runs and their preparation. 20 physics experiments took data at six of the beam intersections. Ten of these experiments were completed. Several new ones will start this year, after the annual shut-down ending March 1st. Again six intersections will be used for physics, including one (I 7) that has now been equipped with a high luminosity insertion. Operational performance throughout the year has profited from the regular application of the methods developed at the end of 1973, viz. gradual compensation of the space-charge tune shift during stacking followed by fine tune corrections with the help of Schottky diagnostics Circulating currents above 15 A and luminosities around 5 × 1030 cm30 s-1 became routine performance, while the beams remained confined to the space of the tune diagram marked 8C in Fig. 1. This space is free of non-linear resonances below the order 8. In addition, a further improvement of the pressure to values well below 10-11 torr average around the two rings, has led to improved clearing of ionization electrons. As a result, decay rates as low as 3 × 10-5 fractional loss of current per hour have often been observed. More than half of this decay is due to beam-beam collisions, the rest to nuclear collisions with the residual gas. These conditions permitted running at the highest luminosity while all experiments could take data, undisturbed by excessive background.