Abstract
The coupled-bunch instability for arbitrary multibunch configurations is investigated in its generality. The theoretical framework adopted is based on the general eigenvalue analysis based on the known formulas of the complex frequency shifts for the uniform multibunch configuration case. Closed formulas are derived for special cases. For the configuration consisting of a uniform filling pattern with a gap of missing bunches, the theoretical results are found to be in good agreement with measurements of the transverse coupled-bunch instability driven by the resistive wall impedance performed at the NSLS-II storage ring.
Highlights
The design of modern light sources, with their goal to store beams with low-emittance and high-average current, requires detailed studies to minimize detrimental effects on the beam quality induced by short- and long-range wakefields
The coupled-bunch instability threshold as a function of the gap has been determined experimentally from the stability of Beam Position Monitor (BPM) measurements as discussed in Fig. 5 where the measurements performed at different average currents are shown for the case Mg 1⁄4 M − g 1⁄4 600 and Mg 1⁄4 M − g 1⁄4 1200, where g is the gap in the maximal (M 1⁄4 1320) uniform filling pattern, with the measurements of all the other cases showing a similar behavior
We discussed theoretically the coupled-bunch instability for arbitrary multibunch configurations and benchmarked its predictions against measurements performed at the NSLS-II storage rings
Summary
The design of modern light sources, with their goal to store beams with low-emittance and high-average current, requires detailed studies to minimize detrimental effects on the beam quality induced by short- and long-range wakefields These wakefields are generated by the electromagnetic interaction of the circulating beam with the storage ring vacuum components and, acting back on the beam, determine current dependent instability thresholds that can pose severe limitations to the achievable beam current [1]. We neglect shortrange wakefields and the important head-tail damping effect at positive chromaticity, as well as the effect from a transverse bunch-by-bunch feedback system, all crucial ingredients for stabilizing standard modes of operation in storage rings Such effects are taken into account, for example, in the nested head-tail Vlasov solver discussed in Ref.
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