Abstract
The coherent synchrotron radiation (CSR) of a high-brightness electron beam traversing a series of dipoles, such as transport or recirculation arcs, may result in beam phase space degradation. On one hand, CSR can perturb electron transverse motion in dispersive regions along the beam line and possibly cause emittance growth. On the other hand, the CSR effect on the longitudinal beam dynamics could result in microbunching instability. For transport arcs, several schemes have been proposed to suppress the CSR-induced emittance growth. Correspondingly, a few scenarios have been introduced to suppress CSR-induced microbunching instability, which however mostly aim for linac-based machines. In this paper we provide sufficient conditions for suppression of CSR-induced microbunching instability along transport or recirculation arcs. Examples are presented with the relevant microbunching analyses carried out by our developed semianalytical Vlasov solver [C.-Y. Tsai, D. Douglas, R. Li, and C. Tennant, Linear microbunching analysis for recirculation machines, Phys. Rev. ST Accel. Beams 19, (2016)]. The example lattices include low-energy ($\ensuremath{\sim}100\text{ }\text{ }\mathrm{MeV}$) and high-energy ($\ensuremath{\sim}1\text{ }\text{ }\mathrm{GeV}$) recirculation arcs, and medium-energy compressor arcs. Our studies show that lattices satisfying the proposed conditions indeed have microbunching gain suppressed. Beam current dependences of maximal CSR microbunching gains are also demonstrated, which should help outline a beam line design for different scales of nominal currents. We expect this analysis can shed light on the lattice design approach that aims to control the CSR-induced microbunching.
Highlights
Coherent synchrotron radiation (CSR) has been recognized as one of the most challenging issues for highbrightness beam transport line and recirculation machine designs, in which the beam phase-space quality is always aimed to preserve as well as possible before the beam fulfills its scientific mission or is transported to a subsequent beam line complex
The coherent synchrotron radiation (CSR) of a high-brightness electron beam traversing a series of dipoles, such as transport or recirculation arcs, may result in beam phase space degradation
In this paper we provide a set of sufficient conditions for suppression of CSR-induced microbunching in arcs, which usually consist of several to tens of bending magnets
Summary
Coherent synchrotron radiation (CSR) has been recognized as one of the most challenging issues for highbrightness beam transport line and recirculation machine designs, in which the beam phase-space quality is always aimed to preserve as well as possible before the beam fulfills its scientific mission or is transported to a subsequent beam line complex. When the accumulation of energy modulation by LSC from the upstream section of beam line is significant, the downstream density modulation converted through the global momentum compaction R56ðsÞ (pure optics effect) can result in serious microbunching instability, in particular for nonisochronous arcs. This is referred to as the energy-to-density microbunching amplification. More complete analysis should include the effect of collective interaction and the information of upstream beam line lattice The consideration of such energy-to-density configuration has been beyond the scope of the paper. We conclude the results and comment on the difference of conditions between the transverse CSR emittance compensation and the longitudinal CSR microbunching suppression
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