Synchro-betatron Resonance of Crab Crossing Scheme with Large Crossing Angle and Finite Bunch Length

TL;DR

This paper investigates the nonlinear beam dynamics in crab crossing schemes with large crossing angles and finite bunch length, revealing higher-order resonances that affect beam quality and luminosity, and proposing mitigation strategies.

Contribution

It provides the first detailed analysis of synchro-betatron resonances in crab crossing with large angles and finite bunch length, combining analytical and numerical methods.

Findings

Higher-order synchro-betatron resonances can be excited in the scheme.

These resonances cause beam quality deterioration and luminosity loss.

Countermeasures can effectively suppress the resonances.

Abstract

Crab crossing scheme is an essential collision scheme to achieve high luminosity for the future colliders with large crossing angles. However, when bunch length of one or both colliding beams is comparable with the wavelength of the crab cavity voltage, the nonlinear dependence of the crabbing kick may present a challenge to the beam dynamics of the colliding beams and impact the beam quality as well as the luminosity lifetime. In this paper, the results of nonlinear dynamics in the crab crossing scheme are presented, using both analytical and numerical studies. The result indicates that higher-order synchro-betatron resonances may be excited in the crab crossing scheme with large crossing angle, which causes the beam quality deterioration and luminosity degradation. The studies also reveal possible countermeasures to suppress the synchro-beta resonance, hence mitigate the degradation of beam quality and luminosity.