Electron Cloud Effects – Observations, Mitigation Measures, and Challenges in Rhic and Sns

Electron cloud is one of the leading mechanisms that limit the performance of high intensity circular accelerators and colliders. In the Relativistic Heavy Ion Collider, multibunch electron cloud effects are observed both in the warm region and super-conducting region when the number of ion bunches and their intensities are raised beyond the design values. Vacuum-pressure rises, transverse tune shifts, and electron detector signals are observed at injection, upon transition crossing, and at top energy. Transverse emittance growth, fast instabilities, and beam loss also occur upon transition crossing. With the Spallation Neutron Source Ring, single-bunch electron cloud effects are expected for the high intensity proton beam. A comprehensive list of mitigation measures are implemented both to reduce the production of electron cloud and to control the beam stability. This paper intends to provide an overview of observations, performance limitations, and beam dynamics challenges pertaining to electron cloud build-up in high intensity, circular hadron accelerators.