Experimental study of integer resonance crossing in a nonscaling fixed field alternating gradient accelerator with a Paul ion trap

K Moriya,S Machida,K Ito,H Okamoto,S L Sheehy,C R Prior,K Fukushima,T Okano,D J Kelliher

doi:10.1103/physrevstab.18.034001

Abstract

We present an experimental study aimed at exploring integer resonance crossing with a focus on nonscaling fixed field alternating gradient accelerators. The method uses the Simulator of Particle Orbit Dynamics system at Hiroshima University based on a compact ion trap known as a Paul trap. In a setup that mimics the Electron Model for Many Applications nonscaling fixed field alternating gradient accelerator, we have verified the theoretical prediction of the coherent excitation of dipole motion over a wide range of errors and crossing speeds. In addition, the cancellation of amplitude growth dependent on the relative betatron oscillation phase between two consecutive resonances is observed and studied. We also explore nonlinear effects and, in particular, the effects of amplitude-dependent tune shifts and find that these nonlinear effects are a key factor in understanding our experimental results.

Highlights

The nonscaling fixed field alternating gradient (NS-FFAG) accelerator concept was invented in the 1990s [1,2,3,4] primarily for the acceleration of muons [5,6]
The scaling properties satisfied by the magnetic field By 1⁄4 B0ðr=r0Þk maintain a constant betatron tune, where By is the vertical magnetic field, r is the distance from the machine center, B0 is the vertical magnetic field at r 1⁄4 r0, and k is the field index
After explaining the correspondence between plasma parameters in Simulator of Particle Orbit Dynamics (S-POD) and beam parameters in the NS-FFAG, we show experimentally that resonant instabilities can be excited at integer bare tunes with the addition of a rf dipole field

Summary

Introduction

The nonscaling fixed field alternating gradient (NS-FFAG) accelerator concept was invented in the 1990s [1,2,3,4] primarily for the acceleration of muons [5,6]. The orbits of different momenta are no longer photographic enlargements of each other (i.e., geometric similarity) and focal length no longer scales with the orbit radius (i.e., constant field index k at corresponding orbit points) in the nonscaling version. Both varieties of FFAG have since gained attention for their potential use in other applications including hadron therapy and as high power drivers for neutron production [8,9,10,11,12,13].

Methods

Findings

Discussion

Conclusion