Coherent Beam-Beam Instability in Collisions with a Large Crossing Angle.

K Ohmi,F Zimmermann,N Kuroo,D Zhou,K Oide

doi:10.1103/physrevlett.119.134801

Abstract

In recent years the "crab-waist collision" scheme [P. Raimondi, Proceedings of 2nd SuperB Workshop, Frascati, 2006.; M. Zobov etal., Phys. Rev. Lett. 104, 174801 (2010)PRLTAO0031-900710.1103/PhysRevLett.104.174801] has become popular for circular e^{+} e^{-} colliders. The designs of several future colliders are based on this scheme. So far the beam-beam effects for collisions under a large crossing angle with or without crab waist were mostly studied using weak-strong simulations. We present here strong-strong simulations showing a novel strong coherent head-tail instability, which can limit the performance of proposed future colliders. We explain the underlying instability mechanism starting from the "cross-wake force" induced by the beam-beam interaction. Using this beam-beam wake, the beam-beam head tail modes are studied by an eigenmode analysis. The instability may affect all collider designs based on the crab-waist scheme. We suggest an experimental verification at SuperKEKB during its commissioning phase II.

Highlights

Recent and future eþ e− colliders adopt a collision scheme with a large horizontal crossing (Piwinski) angle σzθc=σx ≫1 [1], where θc is the half crossing angle
We present here strong-strong simulations showing a novel strong coherent head-tail instability, which can limit the performance of proposed future colliders
Since the second half of 2016 there has been progress on three fronts: First, another BBSS simulation suggested that this new instability can be experimentally studied at SuperKEKB, during its upcoming phase II of commissioning

Summary

Introduction

Recent and future eþ e− colliders adopt a collision scheme with a large horizontal crossing (Piwinski) angle σzθc=σx ≫1 [1], where θc is the half crossing angle. Coherent Beam-Beam Instability in Collisions with a Large Crossing Angle The beam-beam effects for collisions under a large crossing angle with or without crab waist were mostly studied using weakstrong simulations. We present here strong-strong simulations showing a novel strong coherent head-tail instability, which can limit the performance of proposed future colliders.

Results

Conclusion