Mitigation of envelope instability through fast acceleration in linear accelerators

Abstract

The space-charge driven envelope instability can be of great danger in high intensity accelerators. Linear accelerators were designed to avoid this instability by keeping the zero current phase advance per lattice period below 90 degrees. In this paper, we studied the acceleration effects on the instability in a periodic solenoid and radio-frequency (rf) focusing channel and a periodic quadrupole and rf focusing channel using a three-dimensional envelope model and self-consistent macroparticle simulations. Our results suggest that the envelope instability might be dramatically mitigated with a reasonable accelerating gradient in both channels. This suggests that the zero current phase advance without acceleration might be above 90 degrees in linear accelerators where the accelerating gradient is sufficiently high.