Experiment on space charge driven nonlinear resonance crossing in an ion synchrotron

G Franchetti,C Omet,P Forck,F Becker,A Parfenova,W Bayer,P Schütt,M Kirk,T Mohite,T Giacomini,O Chorniy,I Hofmann

doi:10.1103/physrevstab.13.114203

Abstract

Trapping of particles in nonlinear resonances in the presence of space charge and synchrotron motion may be a source of beam halo generation and beam loss in high intensity synchrotrons, in particular for extended storage times at the injection plateau as planned for the SIS100 synchrotron of the FAIR project. Although extensive simulation studies have theoretically demonstrated this mechanism, experimental evidence was so far limited to demonstration experiments at the CERN Proton Synchrotron (PS) in 2002--2003 using an octupolar resonance. Here we describe new experiments at the SIS18 synchrotron at GSI, where the resonance is driven by a sextupolar field error and horizontal static tune scans are taken across the resonance stop band. The new data significantly extend the previous observations by a complete set of measurements comparing beams with and without rf, both at low and high intensity. The correlation between transverse beam loss and simultaneous bunch length shortening provides strong evidence that the measured emittance and the loss in intensity are indeed caused by periodic resonance crossing, leading to the main effect of scattering but also to a lesser extent to the trapping of particles due to the combined effect of the nonlinear resonance and the space charge.

Highlights

The dynamics of particle beams in circular accelerators is naturally subject to the periodicity of the sequence of elements composing an accelerator
From this table we find that the ratio between the simulated and experimental maximum emittance growth lies in the range [1.32, 1.45]: The high intensity coasting beam has a maximum emittance growth which is nearly the same in both experiment and simulations
The overall bunch dynamics is characterized by particles which are subjected by a different level of scattering almost reaching a trapping condition. In this experiment we have studied the interplay between the transverse space charge of a bunched beam and a 3rd order lattice resonance

Summary

Introduction

The dynamics of particle beams in circular accelerators is naturally subject to the periodicity of the sequence of elements composing an accelerator. (2) If the tunes cross the resonance fast enough, beam particles will receive a small kick by the stable islands and each single particle invariant will be ‘‘scattered.’’ The distinction between trapping and scattering regimes can be made via an adiabaticity parameter T 1⁄4 1⁄2@jx~fðnÞj=@n=ðQisl:Áx"Þ, where x~f is the position of the fixed points, Qisl: is the secondary tune (island tune), and Áx" the island size. This definition is equivalent to that used in Ref. This approximation is said of the frozen system as the tunes experienced by a beam particle are instantaneous tunes

Methods

Findings

Discussion

Conclusion