Experimental background for rf upgrade in the relativistic heavy ion collider

The electron cloud induced experimental background has been a concern in heavy ion and polarized proton operations in the Relativistic Heavy Ion Collider. This background comes from the beam–gas collisions, and the electron cloud induced dynamic pressure rise at the interaction regions is a culprit. In recent proton runs, a dependence of the electron cloud on bunch length at the beam acceleration and store has been observed. For given beam intensity, shorter bunches produce stronger electron multipacting. The RHIC rf upgrade plan calls for shorter bunches at store, therefore, this background may become a luminosity limiting factor. The observation of the electron cloud induced background is reported, and the issues relevant to the RHIC rf upgrade are studied.