论文标题
CERN超级质子同步器中质子束的纵向模式耦合不稳定性
Longitudinal mode-coupling instabilities of proton bunches in the CERN Super Proton Synchrotron
论文作者
论文摘要
在本文中，我们研究了在CERN超级质子同步加速器（SPS）中观察到的单束稳定性。根据线性化的弗拉索夫理论，径向或方位角模式耦合不稳定性是由于束振荡模式的耦合而产生的，分别属于相同或相邻的方位角模式。我们表明，通过应用Oide-Yokoya方法来计算SPS的逼真的纵向阻抗模型来计算货车Kampen模式。结果与大颗粒模拟一致，并且与光束测量值一致。特别是，我们看到在最近的阻抗运动（2018-2021）之前观察到的单束束的不受控制的纵向发射爆炸是由于径向模式耦合的不稳定性所致。出乎意料的是，这种不稳定性与方位角模式耦合不稳定性一样强，这在SPS中是可能的其他长度和强度组合。我们还证明了RF非线性和电势扭曲在确定这些不稳定性阈值中的重要作用。最后，我们讨论了近期阻抗运动对单人和双RF配置中光束稳定性的影响。
In this paper, we study single-bunch instabilities observed in the CERN Super Proton Synchrotron (SPS). According to the linearized Vlasov theory, radial or azimuthal mode-coupling instabilities result from a coupling of bunch-oscillation modes, which belong to either the same or adjacent azimuthal modes, respectively. We show that both instability mechanisms exist in the SPS by applying the Oide-Yokoya approach to compute van Kampen modes for the realistic longitudinal impedance model of the SPS. The results agree with macroparticle simulations and are consistent with beam measurements. In particular, we see that the uncontrolled longitudinal emittance blow-up of single bunches observed before the recent impedance reduction campaign (2018-2021) is due to the radial mode-coupling instability. Unexpectedly, this instability is as strong as the azimuthal mode-coupling instability, which is possible in the SPS for other combinations of bunch length and intensity. We also demonstrate the significant role of rf nonlinearity and potential-well distortion in determining these instability thresholds. Finally, we discuss the effect of the recent impedance reduction campaign on beam stability in single- and double-rf configurations.
