arXiv subjects
Publications and source records attributed to Georg Heinz Hoffstaetter.
This is the Snowmass Whitepaper on Beam Test Facilities for R&D in Accelerator Science and Technologies and it is submitted to two topical groups in the Accelerator Frontier: AF1 and AF6.
In a multipass energy recovery linac (ERL), each cavity must regain all energy expended from beam acceleration during beam deceleration, and the beam should achieve specific energy targets during each loop that returns it to the linac. For full energy recovery, and for every returning beam to meet loop energy requirements, we must specify and maintain the phase and voltage of cavity fields in addition to selecting adequate flight times. These parameters are found with a full scale numerical optimization program. If we impose symmetry in time and energy during acceleration and deceleration, fewer parameters are needed, simplifying the optimization. As an example, we present symmetric models of the Cornell BNL ERL Test Accelerator (CBETA) with solutions that satisfy the optimization targets of loop energy and zero cavity loading. An identical cavity design and nearly uniform linac layout make CBETA a potential candidate for symmetric operation.
This paper uses theory and simulation of the Beam Break-Up instability (BBU) for multi-turn ERLs to determine and to optimize the current limit of the Cornell Brookhaven Energy-Recovery-Linac Test Accelerator (CBETA). Currently under construction at Cornell University's Wilson Laboratory, the primary structures of CBETA for beam recirculation include the Main Linac Cryomodule and the Fixed Field Alternating Gradient beamline. As the electron bunches pass through the MLC cavities, Higher Order Modes (HOMs) are excited. The recirculating bunches return to the cavities to further excite HOMs, and this feedback loop can give rise to BBU. We will first explain how BBU effect is simulated using the tracking software BMAD, and check the agreement with the BBU theory for the most instructive cases. We then present simulation results on how BBU limits the maximum achievable current of CBETA with different HOM spectra in the cavities. Lastly we investigate ways to improve the threshold current of CBETA.