Review of impedance-induced instabilities and their possible mitigation techniques

Broadband Impedance Calculations and Single Bunch Instabilities Estimations of the HLS-II storage ring

The upgrade project of Hefei Light Source storage ring is under way. In this paper, the broadband impedances of resistive wall and coated ceramic vacuum chamber were calculated using the analytic formula, the wake fields and impedances of other designed vacuum chambers have been simulated by the CST code, and then the broadband impedances model was obtained. Using the theoretical formula, longitudinal and transverse single bunch instabilities were discussed. With the carefully-designed vacuum chamber, we find that the thresholds of the beam instabilities are higher than the beam current goal.

Impedances and Instabilities

The concepts of wake fields and impedance are introduced to describe the electromagnetic interaction of a bunch of charged particles with its environment in an particle accelerator. The wake fields can act back on the beam and lead to instabilities, which may limit the achievable current per bunch, the total current, or even both. Some typical examples are used to illustrate the wake function and its basic properties. Then the frequency-domain view of the wake field or impedance is explained, and basic properties of the impedance are derived. The impedance of a cavity mode is illustrated using…

Transverse modes and instabilities of a bunched beam with space charge and resistive wall impedance

Transverse instability of a bunched beam is investigated with synchrotron oscillations, space charge, and resistive wall wakefield taken into account. Boxcar model is used for all-round analysis, and Gaussian distribution is invoked for details. The beam spectrum, instability growth rate and effects of chromaticity are studied in a wide range of parameters, both with head-tail and collective bunch interactions included. Effects of the internal bunch oscillations on the of collective instabilities is investigated thoroughly. Landau damping caused by the space charge tune spread is discussed, an…

Efficiency of feedbacks for suppression of transverse instabilities of bunched beams

Which gain and phase have to be set for a bunch-by-bunch transverse damper, and at which chromaticity it is better to stay? These questions are considered for three models: the two-particle model with possible quadrupole wake, the author's Nested Head-Tail Vlasov solver with a broadband impedance, and the same with the LHC impedance model.

Beam Coupling Impedance Measurement and Mitigation for a TOTEM Roman Pot

The longitudinal and transverse beam coupling impedance of the first final TOTEM Roman Pot unit has been measured in the laboratory with the wire method. For the evaluation of transverse impedance the wire position has been kept constant, and the insertions of the RP were moved asymmetrically. With the original configuration of the RP, resonances with fairly high Q values were observed. In order to mitigate this problem, RF-absorbing ferrite plates were mounted in appropriate locations. As a result, all resonances were sufficiently damped to meet the stringent LHC beam coupling impedance requi…

高强度直线加速器：动力学、不稳定性及缓解措施

High-intensity LINACS: Dynamics, Instabilities and Mitigations

本文探讨了重离子直线加速器中强度限制的问题，分析了其在不同加速器类型中的差异，并介绍了束流动力学及缓解措施的实例。