Beam Induced Multipacting

Beam induced multipacting driven by the electric field of successive bunches, as first observed in the ISR proton-proton storage ring [1] may arise from a resonance motion of a cloud of secondary electrons bouncing back and forth between opposite walls of the vacuum chamber. Under conditions where the average secondary electron yield of this process exceeds unity, the electron cloud may increase exponentially. A consequence for the vacuum system is strong electron stimulated gas desorption and the associated pressure increase which may affect the beam lifetime. A simple criterion for the onset of multipacting and an estimate of the average secondary electron yield is derived and will be applied to typical vacuum chambers and to the specific conditions found in the LHC.