Mitigation of envelope instability through fast acceleration

TL;DR

This paper investigates how increasing the accelerating gradient in high-intensity linear accelerators can mitigate space-charge driven envelope instability, allowing for phase advances above 90 degrees and enhancing accelerator design flexibility.

Contribution

It demonstrates through simulations that sufficient acceleration can suppress envelope instability, challenging traditional design constraints based on phase advance limits.

Findings

Envelope instability can be mitigated with higher accelerating gradients.

Higher gradients allow phase advances above 90 degrees.

Design flexibility in accelerators is increased with this mitigation.

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 report on 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. The simulation results show that the envelope instability can be mitigated with a reasonable accelerating gradient in both channels. This suggests that the zero current phase advance might be above 90 degrees in linear accelerators where the accelerating gradient is sufficiently high and opens additional freedom of transverse and longitudinal focusing in the accelerator design.