Review of scaled penning H- surface plasma source with slit emitters for high duty factor linacs

The Penning H- surface plasma source (SPS) has been used at Rutherford Appleton Laboratory (RAL) for 20 years to provide the required H- beams for charge-exchange injection into the 800-MeV proton synchrotron on the ISIS spallation neutron source. The RAL source is based on the first H- Penning SPS operated at Los Alamos. Since that original technology exchange, Los Alamos has developed scaled-up versions of the Penning H- SPS with the goal of extending the H- beam duty factor (df) while maintaining high beam brightness. A 250-mA H- beam with rms normalized emittance of <0.3 (πmm-mrad) in both transverse planes has been extracted from a 4X scaled Penning source at a discharge df of 0.5%. Using discharge scaling laws and the 250 mA H- current results, it is predicted that a 4X Penning H- SPS with a slit emitter would be capable of producing >100-mA, low emittance H- beams in the 5% df range. A source with these parameters would be suitable for the European Spallation Source (ESS) and other high-power proton driver projects