Stability of compact recirculating accelerators

Beam stability in high-current recirculating accelerators using magnetic beam transport is investigated. The authors focus on three instabilities which have the potential for causing beam disruption: the three-wave, negative-mass and beam breakup instabilities. The three-wave instability is a parametric instability caused by strong-focusing fields like the helical quadrupole in the SLIA (spiral line induction accelerator). The authors have obtained approximate analytic expressions for the growth rate and the convection velocity of this instability. A simple numerical simulation code E3WAVE has been written to model the linear behavior of the instability. Its results confirm the analytic results in the appropriate limits. The authors have used E3WAVE to make predictions for the SLIA experiments presently under way. The authors also have investigated the short-wavelength negative-mass instability modes, which interact resonantly with cavity modes of the drift-tube