Differential current measurement in the BNL energy recovery linac test facility

Abstract

An energy recovery linac (ERL) test facility is presently under construction at BNL [V.N. Litvinenko, et al., High current energy recovery linac at BNL, PAC, 2005; I. Ben-Zvi, et al., Extremely high current, high brightness energy recovery linac, PAC, 2005]. The goal of this test facility is to demonstrate CW operation with an average beam current greater than 100 mA, and with greater than 99.95% efficiency of current recovery. This facility will serve as a test bed for the novel high current CW photo-cathode [A. Burrill, et al., Multi-alkali photocathode development at BNL, PAC, 2005; A. Murray, et al., State-of-the-art electron guns and injector designs for energy recovery linacs, PAC, 2005], the superconducting RF cavity with HOM dampers [R. Calaga, et al., High current superconducting cavities at RHIC, EPAC, 2004; R. Calaga, et al., in: Proceedings of the 11th workshop on RF superconductivity, Lubeck, Germany, 2003], and the lattice [D. Kayran, V. Litvinenko, Novel method of emittance preservation in ERL merging system in presence of strong space charge forces, PAC, 2005; D. Kayran, et al., Optics for high brightness and high current ERL project at BNL, PAC, 2005] and feedback systems needed to insure the specified beam parameters. It is an important stepping stone for electron cooling in RHIC [I. Ben-Zvi, et al., Electron cooling of RHIC, PAC, 2005], and essential to meet the luminosity specifications of RHICII [T. Hallman, et al., RHICII/eRHIC white paper, available at http://www.bnl.gov/henp/docs/NSAC_RHICII-eRHIC_2-15-03.pdf]. The expertise and experience gained in this effort might also extend forward into a 10–20 GeV ERL for the electron-ion collider eRHIC [ http://www.agsrhichome.bnl.gov/eRHIC/, Appendix A, The linac-ring option, 2005]. We report here on the use of a technique of differential current measurement to monitor the efficiency of current recovery in the test facility, and investigate the possibility of using such a monitor in the machine protection system.