Landau damping via the harmonic sextupole

Lidia Tosi,Emanuel Karantzoulis,Victor Smaluk

doi:10.1103/physrevstab.6.054401

Lidia Tosi, Emanuel Karantzoulis + Show 1 more

Open Access

https://doi.org/10.1103/physrevstab.6.054401

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Abstract

Multibunch instabilities of a storage ring electron beam occur due to coherent particle oscillations generated through a bunch to bunch coupling via the impedances, deteriorating the beam quality. One cure for multibunch instabilities is Landau damping, i.e., introducing a spread in the oscillation frequencies among the particles of the individual bunches in order to destroy the coherence of the coupled multibunch oscillation. Measurements at ELETTRA have shown that the harmonic sextupole provides Landau damping capable of suppressing transverse multibunch instabilities. The damping is induced by the nonlinear tune spread with amplitude among the electrons within the individual bunches.

Highlights

The presence of multibunch instabilities is one of the most common reasons for beam quality deterioration and current limitation in storage rings
One cure for multibunch instabilities is to introduce a spread in the oscillation frequencies among the particles of the individual bunches in order to destroy the coherence of the coupled multibunch oscillation
As the coherent oscillations build up a center of mass motion, the latter starts decreasing as particles go out of phase with respect to each other and decohere

Summary

INTRODUCTION

The presence of multibunch instabilities is one of the most common reasons for beam quality deterioration and current limitation in storage rings. Where the subscripts x and y denote the horizontal and vertical planes, respectively, u x; y are the nonlinear tune shifts, Ju the perturbed action variables, and C11; C12; C22 are coefficients which depend on the sextupole strengths, on the beta functions at their locations, and on the relative phase advances between them [2,3]. Similar observations have been made for the vertical plane, due to the relatively simpler mechanism, both measurements and simulations presented are related to the horizontal plane In this case, the coupling among the two planes due to the sextupoles is eliminated and the tune shift with amplitude may be reduced to x C11 2Jx provided that the collective motion is principally in the horizontal plane.

LANDAU DAMPING OBSERVATION

MACROSCOPIC INSTABILITY MEASUREMENTS

INSTABILITY MEASUREMENTS WITH THE TMBF

CONCLUSIONS