Abstract
For a high-brightness electron beam with low energy and high bunch charge traversing a recirculation beamline, coherent synchrotron radiation and space charge effect may result in the microbunching instability (MBI). Both tracking simulation and Vlasov analysis for an early design of Circulator Cooler Ring for the Jefferson Lab Electron Ion Collider reveal significant MBI. It is envisioned these could be substantially suppressed by using a magnetized beam. In this work, we extend the existing Vlasov analysis, originally developed for a non-magnetized beam, to the description of transport of a magnetized beam including relevant collective effects. The new formulation will be further employed to confirm prediction of microbunching suppression for a magnetized beam transport in a recirculating machine design.
Highlights
AND MOTIVATIONBeam quality preservation is of general concern in delivering a high-brightness electron beam through a transport line or recirculation arc in the design of modern accelerators
It is found that the smearing effect in the longitudinal beam phase space originates from the large transverse beam size as a nature of the magnetized beams and becomes effective through the x − z correlation when the correlated distance is larger than the microbunched scale
Our study indicates that the preliminary design of circulator cooler ring (CCR) for high-energy electron cooling is at risk of microbunching instability; an improved design is required to suppress such instability and/or alternative beam transport schemes should be considered in order to compensate and to circulate the electron beam as many turns as possible while maintaining the high phase space quality of the electron beam required by electron cooling efficiency
Summary
Beam quality preservation is of general concern in delivering a high-brightness electron beam through a transport line or recirculation arc in the design of modern accelerators. These usually set stringent requirements on electron beam brightness because the high peak bunch current and low energy would enhance the collective interaction, and small beam emittance or energy spread would weaken Landau damping or the phase-space smearing effect Both tracking simulations [6,7] and Vlasov analysis [8,9,10] have shown that MBI is a serious concern for the early CCR design. A magnetized beam cooling was found to be an extremely useful technique in obtaining high-brightness hadron beams with low longitudinal momentum spread [22] Another advantage of using magnetized beams has been suggested, because it was believed to mitigate some collective effects such as space charge [24] and MBI (our primary focus in this paper) because of its relatively larger transverse beam size.
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