Intense ion beams in the Brookhaven Relativistic Ion Collider lead to a rise in the vacuum pressure. Electron clouds can contribute to such a process. To measure electron cloud densities the coherent tune shift along the bunch train was observed with different bunch spacings and intensities. From the measured coherent tune shifts, electron cloud densities are computed and compared with densities obtained in electron cloud simulations.

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Since 2001, the Relativistic Heavy Ion Collider has experienced electron cloud effects, some of which have limited the beam intensity. These include dynamic pressure rises (including pressure instabilities), tune shifts, a reduction of the instability threshold for bunches crossing the transition energy, and possibly incoherent emittance growth. We summarize the main observations in operation and dedicated experiments as well as countermeasures including baking, nonevaporable getter coated warm beam pipes, solenoids, bunch patterns, antigrazing rings, prepumped cold beam pipes, scrubbing, and operation with long bunches.

Bunched beam stochastic cooling in the Relativistic Heavy Ion Collider (RHIC) at 100 GeV has been achieved. The longitudinal cooling system is designed for heavy ion operation but was tested using protons. A very low intensity bunch with 10 9 protons was prepared so that cooling times and voltage requirements would be comparable to the heavy ion case. With this bunch a cooling time of the order of an hour was observed through shortening of the bunch length and narrowing of the Schottky lines.