Advances in the Performance of the SNS Ion Source

The ion source developed for the Spallation Neutron Source (SNS) is a radio frequency, multi-cusp source designed to produce ∼ 40 mA of H^-with a normalized rms emittance of less than 0.2 π · mm · mrad. To date the source has been utilized in commissioning the SNS accelerator, delivering beams of 10-50 mA with duty-factors of typically ∼ 0.1% for operational periods of several weeks, achieving an availability of ∼ 99%. Ultimately the SNS facility will require beam duty-factors of 6% (1 ms pulse length, 60 Hz repetition rate, 21 day run-period). Over the last year, several experiments were performed in which the ion source was continuously operated at full duty-factor and maximum beam current on a test stand. Average beam attenuation rates of ∼ 5 mA/day were observed and beams in excess of 30 mA could only be sustained for periods of several hours. Recently, a breakthrough in our understanding of the Cs release process has led to the development of a new source conditioning technique which resulted in a dramatic increase in beam persistence with time. H^-beam attenuation rates have been improved to ∼ 0.4 mA/day, allowing beams in excess of 30 mA to be delivered continuously at full duty factor for periods of ∼ 16 days.