BEAM BREAKUP INSTABILITY IN RF LINACS

Analytic and numerical calculations of the beam breakup instability in rf linac cavities are presented. Analytic calculations for single bunch beam breakup in pillbox cavities show that beam deflection x scales with initial deflection xo, charge per bunch Q, accelerating gradient E, , accelerator length z, and cavity wavelength X as x=x0 [ ’ +,,i::4,:3]. This scaling is generalized to include the effects of periodic focusing on transverse emittance growth. Numerical simulations of multibunch beam breakup show growth of beam deflection amplitude from wake fields generated by preceding bunches. Wake field calcula-tions using a transverse beam cavity interaction code are presented