Response of colliding beam-beam system to harmonic excitation due to crab-cavity rf phase modulation

K Ohmi,F Zimmermann,K Oide,K Nakanishi,R Calaga,T Ieiri,R Tomás,M Tobiyama,Y Sun,Y Ohnishi,Y Morita,Y Funakoshi

doi:10.1103/physrevstab.14.111003

Abstract

During 2008 and 2009 dedicated beam experiments with crab cavities were performed in the KEKB. The goal was to measure the impact of crab-cavity radio frequency (rf) noise on the beam quality. These experiments were performed as a validation of the crab-cavity beam dynamics models in view of the possible use of crab cavities in the upgrade of the CERN Large Hadron Collider (LHC). An unexpected strong beam-beam instability was observed during the course of the experiments as a kind of frequency response. Understanding this finding required extensive multiparticle and single particle simulations plus an extra experimental session to consolidate the observations.

Highlights

The KEKB is an asymmetric electron-positron collider
Unlike the KEKB, the Large Hadron Collider (LHC) features a negligible synchrotron radiation damping. This calls for the use of accurate models of crab-cavity beam dynamics in order to validate an LHC upgrade based on crab cavities
Beam experiments at the KEKB were conducted in order to study two critical aspects, the impact of crab-cavity rf noise on the beam quality and techniques to measure the crab dispersion

Summary

INTRODUCTION

The KEKB is an asymmetric electron-positron collider. The accelerator consists of a 3.5 GeV positron storage ring (LER) and an 8 GeV electron ring (HER) [1]. The KEKB has achieved a new world record luminosity 2:1 Â 1034 cmÀ2 sÀ1 in 2009 after the installation of one crab cavity per ring in 2007. These cavities give a time dependent transverse deflection to the beams that results in head-on collisions at the interaction point (IP). Unlike the KEKB, the LHC features a negligible synchrotron radiation damping This calls for the use of accurate models of crab-cavity beam dynamics in order to validate an LHC upgrade based on crab cavities. The phase noise of the KEKB crab cavities is dominated by a set of discrete frequencies [2]. The beam-beam modes are defined by an eigensystem of the matrix product of revolution and linear beambeam kick,

Number of bunches

Measurement Simulation

Relative luminosity

CONCLUSIONS