Multibunch beam breakup in high energy linear colliders

The SLAC (Stanford Linear Accelerator Center) design for a next-generation linear collider with center-of-mass energy of 0.5 to 1.0 TeV requires that multiple bunches (~10) be accelerated on each RF fill. At the beam intensity (~10¹⁰ particles per bunch) and RF frequency (11 to 17 GHz) required, the beam would be highly unstable transversely. Using computer simulation and analytic models, several possible methods of controlling the transverse instability were studied: (1) using damped cavities to damp the transverse dipole modes; (2) adjusting the frequency of the dominant transverse mode relative to the RF frequency, so that bunches are placed near zero crossings of the wake; (3) introducing a cell-to-cell spread in the transverse dipole mode frequencies; and (4) introducing bunch-to-bunch variation in the transverse focusing. It is shown that the best cures to use depend on the bunch spacing, intensity, and other features of the final design