Beam Stacking Experiment at a Fixed Field Alternating Gradient Accelerator

TL;DR

This paper reports an experimental demonstration of beam stacking in a fixed field accelerator, showing potential for increasing particle beam intensity with minimal momentum spread increase, despite some beam loss.

Contribution

The study provides the first experimental evidence of beam stacking in a fixed field alternating gradient accelerator, highlighting its feasibility and challenges.

Findings

Successful beam stacking demonstrated at KURNS FFA.

Slight increase in momentum spread observed after stacking.

Significant reduction in beam intensity due to RF knock-out suspected.

Abstract

A key challenge in particle accelerators is to achieve high peak intensity. Space charge is particularly strong at lower energy such as during injection and typically limits achievable peak intensity. The beam stacking technique can overcome this limitation by accumulating a beam at high energy where space charge is weaker. In beam stacking, a bunch of particles is injected and accelerated to high energy. This bunch continues to circulate, while a second and subsequent bunches are accelerated to merge into the first. It also allows the user cycle and acceleration cycles to be separated which is often valuable. Beam stacking is not possible in a time varying magnetic field, but a fixed field machine such as an Fixed Field Alternating Gradient Accelerator (FFA) does not sweep the magnetic field. In this paper, we describe experimental demonstration of beam stacking of two beams at KURNS FFA in Kyoto University. The momentum spread and intensity of the beam was analysed by study of the Schottky signal, demonstrating stacking with only a slight increase of momentum spread of the combined beams. The intensity of the first beam was, however, significantly reduced. RF knock-out is the suspected source of the beam loss.