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Kazimi, R.

Paper Title Page
WEPP087 Observation and Mitigation of Multipass BBU in CEBAF 2722
 
  • R. Kazimi, A. Freyberger, C. Hovater, G. A. Krafft, F. Marhauser, T. E. Plawski, C. E. Reece, J. S. Sekutowicz, C. Tennant, M. G. Tiefenback, H. Wang
    Jefferson Lab, Newport News, Virginia
 
  The CEBAF recirculating accelerator at Jefferson Lab consists of two linacs carrying beam for up to five passes of acceleration. The Beam Break-Up (BBU) phenomenon was anticipated during design of the accelerator. The threshold beam current to induce BBU was calculated to be approximately 20 milliamperes, far above operational current. No sign of BBU was ever seen in more than a decade of operation. A specially designed acceleration cavity in a recently installed cryomodule was found to cause a BBU instability under special conditions with as low as 40 uA of injected beam current. This presented an opportunity to study BBU in a five-pass accelerator. In this paper we will discuss multipass BBU, show observational data, and discuss the ways we have developed to maintain the instability threshold current to values above those required for operation.