Lifetime test on a high-performance DC microwave proton source

Powerful CW proton linear accelerators (100 mA at 0.5-1 GeV) are being proposed for spallation neutron source applications. These production accelerators require high availability and reliability. A microwave proton source, which has already demonstrated several key beam requirements, was operated for one week (170 hours) in a DC mode to test the reliability and lifetime of its plasma generator. The source was operated with 570 W of microwave (2.45 GHz) discharge power and with a 47-kV extraction voltage. This choice of operating parameters gave a proton current density of 250-mA/cm² at 83% proton fraction, which is sufficient for a conservative DC injector design. The beam current was 60-65 mA over most of the week, and was sufficiently focused for RFQ injection. Total beam availability, defined as 47-keV beam-on time divided by elapsed time, was 96.2%. Spark downs in the high voltage column and a gas flow control problem caused all the downtime; no plasma generator failures were observed