Beam-Breakup Studies for the 4-Pass Cornell-Brookhaven Energy-Recovery Linac Test Accelerator

摘要

The Cornell Brookhaven Energy Recovery Linac (ERL) Test Accelerator (CBETA) [1] is currently under construction at Cornell University's Wilson Laboratory. The primary structures in CBETA for beam recirculation include the Main Linac Cryomodule (MLC) and the Fixed Field Alternating Gradient (FFAG) beamline. As the electron bunches pass through the MLC cavities, higher order modes (HOMs) are excited. The recirculating bunches in turn excite HOMs further, and this feedback loop can give rise to beam breakup instability (BBU). We will first explain how BBU occurs and how we simulate the effect. Then we present the simulation results on how BBU limits the maximum achievable current of CBETA, and the potential ways to improve the threshold current.