Beam Dynamics Group Summart

The CERN SPS was the first accelerator to store and collide hadron bunches protons and antiprotons in counter rotating beams. A relatively small number of bunches circulated in a single vacuum chamber, inside normal conducting magnets. Now used mainly as an injector to LEP, the SPS will become the final accelerator in the injection chain supplying the LHC with protons and, at least occasionally, with heavy ions. The Fermilab Tevatron was the second hadron collider to come on the air. Still in operation, it too stores a modest number of proton and antiproton bunches in a single vacuum chamber. In contrast with the SPS, the Tevatron and all subsequent hadron colliders use superconducting magnet technology to achieve higher magnetic fields and to reduce operating costs. Next came the DESY machine H E M , which collides electrons (or positrons) with protons. Because the proton bunches circulate in their own beam pipe, parasitic beam-beam collisions are mainly absent, and a relatively large number of circulating bunches nominally 210 is feasible. Superficially, this is both good and bad for single beam collective effects. The good news is that more bunches allow smaller single bunch populations to deliver the same luminosity, thereby ameliorating single bunch instabilities. In practice, of course, the population tends to remain the same, while the luminosity is increased. The bad news is that the interbunch spacing is greatly decreased, raising the potential vulnerability to multibunch instabilities. The Relativistic Heavy Ion Collider (RBIC) is currently under construction at the Brookhaven National Laboratory. RHIC stores as many as 114 bunches of hadrons heavy ions or protons in two horizontally separated rings of superconducting magnets. Chronologically last, but not least, the LHC will store as many as 2835 bunches of hadrons in two separate beam pipes inside a single superconducting magnet. Table 1 compares the bunch parameters of this list of hadron colliders.