Jin Lihui, Shi Jicong
Department of Physics and Astronomy, The University of Kansas, Lawrence, Kansas 66045, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2004 Mar;69(3 Pt 2):036503. doi: 10.1103/PhysRevE.69.036503. Epub 2004 Mar 31.
In hadron colliders, electron-beam compensation of beam-beam tune spread has been explored for a reduction of beam-beam effects. In this paper, effects of the tune-spread compensation on beam-beam instabilities were studied with a self-consistent beam-beam simulation in model lattices of Tevatron and Large Hodron Collider. It was found that the reduction of the tune spread with the electron-beam compensation could induce a coherent beam-beam instability. The merit of the compensation with different degrees of tune-spread reduction was evaluated based on beam-size growth. When two beams have a same betatron tune, the compensation could do more harm than good to the beams when only beam-beam effects are considered. If a tune split between two beams is large enough, the compensation with a small reduction of the tune spread could benefit beams as Landau damping suppresses the coherent beam-beam instability. The result indicates that nonlinear (nonintegrable) beam-beam effects could dominate beam dynamics and a reduction of beam-beam tune spread by introducing additional beam-beam interactions and reducing Landau damping may not improve the stability of beams.
在强子对撞机中，人们已经探索了利用电子束补偿束流-束流调谐扩展来减少束流-束流效应。本文在Tevatron和大型强子对撞机的模型晶格中，通过自洽的束流-束流模拟研究了调谐扩展补偿对束流-束流不稳定性的影响。研究发现，电子束补偿导致的调谐扩展减小可能会引发一种相干的束流-束流不稳定性。基于束尺寸增长评估了不同程度调谐扩展减小的补偿优点。当两束具有相同的β振荡调谐时，仅考虑束流-束流效应时，补偿对束流可能弊大于利。如果两束之间的调谐分裂足够大，调谐扩展减小量较小的补偿可能会使束流受益，因为朗道阻尼会抑制相干的束流-束流不稳定性。结果表明，非线性（不可积）束流-束流效应可能主导束流动力学，通过引入额外的束流-束流相互作用和降低朗道阻尼来减小束流-束流调谐扩展可能不会提高束流的稳定性。
