大束-束参数非对称相互作用的相干光频移
Coherent Beam-Beam Tune Shift of Unsymmetrical Beam-Beam Interactions with Large Beam-Beam Parameter
摘要：
在HERA中对具有很大束-束参数（高达$ξ_y=0.272$）的轻子束的非对称束-束相互作用的相干束-束调谐漂移进行了实验和数值研究。与束-束相互作用的对称情况不同，在这种非对称情况下，相干和非相干的束-束调谐位移之比随着束-束参数的增加而单调减小.自洽束-束模拟，线性化的弗拉索夫方程，和刚性梁模型的结果与实验测量进行了比较。结果发现，实验测量的相干光束-光束调谐位移与模拟计算的一致性很好，但远小于用线性化Vlasov方程和单模近似或刚性光束模型计算的相干光束-光束调谐位移。研究表明，在非对称束-束相互作用的情况下，Vlasov方程线性化中的单模近似是不成立的。在非对称梁-梁相互作用的情况下，刚性梁模型只适用于小的梁-梁参数。
英文摘要：
Coherent beam-beam tune shift of unsymmetrical beam-beam interactions was studied experimentally and numerically in HERA where the lepton beam has a very large beam-beam parameter (up to $ξ_y=0.272$). Unlike the symmetrical case of beam-beam interactions, the ratio of the coherent and incoherent beam-beam tune shift in this unsymmetrical case of beam-beam interactions was found to decrease monotonically with increase of the beam-beam parameter. The results of self-consistent beam-beam simulation, the linearized Vlasov equation, and the rigid-beam model were compared with the experimental measurement. It was found that the coherent beam-beam tune shifts measured in the experiment and calculated in the simulation agree remarkably well but they are much smaller than those calculated by the linearized Vlasov equation with the single-mode approximation or the rigid-beam model. The study indicated that the single-mode approximation in the linearization of Vlasov equation is not valid in the case of unsymmetrical beam-beam interactions. The rigid-beam model is valid only with a small beam-beam parameter in the case of unsymmetrical beam-beam interactions.
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