This paper discusses novel coherent beam-beam instability in collisions with a large crossing angle. The instability appears in the correlated head-tail motion of two colliding beams. A cross-wake force, which is localized at the collision point, is introduced to represent the head-tail correlation between colliding beams. A mode-coupling theory based on this localized cross-wake force enables us to explain the correlated heal-tail instability. The use of a collision scheme with a large crossing angle is becoming popular in the design of electron--positron colliders. An example thereof is the SuperKEKB project, in which a collision with a large crossing angle is performed to boost the luminosity to $0.8ifmmodeimeselseexttimesi{}{10}^{36}ext{ }ext{ }{mathrm{cm}}^{ensuremath{-}2}ext{ }{mathrm{s}}^{ensuremath{-}1}$. Future circular colliders will also be designed with a large crossing angle. Strong-strong simulations, which have shown the first coherent head-tail instability, can limit the performance of proposed future colliders. The mechanism whereby this instability occurs is mode coupling due to the cross-wake force. This instability may affect all collider designs based on the crab waist scheme.
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机译：本文讨论了在具有大交叉角的碰撞中新型相干光束不稳定性。这种不稳定性出现在两个碰撞光束的相关头尾运动中。引入了位于碰撞点的横向苏醒力来表示碰撞光束之间的头尾相关性。基于这种局部交叉唤醒力的模式耦合理论使我们能够解释相关的愈合尾部不稳定性。在电子-正电子对撞机的设计中，使用具有大交叉角的碰撞方案变得越来越普遍。其示例是SuperKEKB项目，其中执行大交叉角碰撞以将亮度提高到$ 0.8 ifmmode times else texttimes fi {} {10} ^ {36} text {} text {} { mathrm {cm}} ^ { ensuremath {-} 2} text {} { mathrm {s}} ^ { ensuremath {-} 1} $。未来的圆形对撞机也将被设计成具有较大的交叉角。强烈的模拟显示了第一个相干的头尾不稳定性，可能会限制拟议的未来对撞机的性能。发生这种不稳定性的机制是由于交叉唤醒力引起的模式耦合。这种不稳定性可能会影响所有基于蟹腰方案的对撞机设计。
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