Abstract
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.
Highlights
The Relativistic Heavy Ion Collider (RHIC), in operation since 2000, has collided species from gold ions at energies up to 100 GeV=nucleon, to polarized protons at energies up to 100 GeV [1,2]
The RHIC beam pipes in the warm regions are made of stainless steel 304L
Thin-film coating of beam pipes with the nonevaporable getter material TiZrV has been developed at CERN [59,60], and found large-scale application in a number of machines including ESRF [61], RHIC [62,63], LEIR [13], SOLEIL [64], and LHC [65]
Summary
The Relativistic Heavy Ion Collider (RHIC), in operation since 2000, has collided species from gold ions at energies up to 100 GeV=nucleon, to polarized protons at energies up to 100 GeV [1,2]. Since 2001, dynamic pressure rises were observed that limited the beam intensity. At that time the cause of the dynamic pressure rise was not known and electron clouds were suspected as a possible mechanism. With ever increasing beam intensities other phenomena were seen that were caused by electron clouds. We summarize these observations as well as the countermeasures tested and used. After electron clouds were established as the likely leading cause for dynamic pressure rises, a number of cures were tested or implemented. The use of solenoids and antigrazing rings reduces the number of electrons and molecules released from the surface. Optimized bunch patterns and the operation with longer bunches reduce the electron cloud buildup
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