Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
JLab, Newport News, Virginia, USA
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.
*Ya. Derbenev and Y. Zhang, COOL'09 (FRM2MCCO01)
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
JLab, Newport News, Virginia, USA
Microbunching instability (MBI) has been a challenging issue in high-brightness electron beam transport for modern accelerators. The existing Vlasov analysis of MBI is based on single-pass configuration*. For multi-pass recirculation or a long beamline, the intuitive argument of quantifying MBI, by successive multiplication of MBI gains, was found to underestimate the effect**. More thorough analyses based on concatenation of gain matrices aimed to combine both density and energy modulations for a general beamline**. Yet, quantification still focuses on characterizing longitudinal phase space; microbunching residing in (x,z) or (x',z) was observed in particle tracking simulation. Inclusion of such cross-plane microbunching structures in Vlasov analysis shall be a crucial step to systematically characterize MBI for a beamline complex in terms of concatenating individual beamline segments. We derived a semi-analytical formulation to include the microbunching structures in longitudinal and transverse phase spaces. Having numerically implemented the generalized formulae, an example lattice*** is studied and reasonable agreement achieved when compared with particle tracking simulation.
* Heifets et al., PRSTAB 5, 064401 (2002), Huang and Kim, PRSTAB 5, 074401 (2002), and Vneturini, PRSTAB 10, 104401 (2007)
** Tsai et al., IPAC'16 (TUPOR020)
*** Di Mitri, PRSTAB 17, 074401 (2014)
