Recent advances in the performance and understanding of the SNS ion source

The ion source developed for the Spallation Neutron Source (SNS) by Lawrence Berkeley National Laboratory (LBNL), is a radio frequency, multi-cusp source designed to produce ∼ 40 mA of H^- with a normalized rms emittance of less than 0.2 pi mm mrad. To date, the source has been utilized in the commissioning of the SNS accelerator and has already demonstrated stable, satisfactory operation at beam currents of ∼30 mA with duty-factors of ∼0.1% for operational periods of several weeks. Once the SNS is fully operational in 2008, a beam current duty-factor of 6% (1 ms pulse length, 60 Hz repetition rate) will be required in order to inject the accelerator. To ascertain the capability of the source to deliver beams at this high duty-factor over sustained time periods, several experimental runs have been conducted, each ∼1 week in length, in which the ion source was continuously operated on a dedicated test stand. The results of these tests are reported as well as a theory of the Cs release and transport processes which were derived from these data. The theory was then employed to develop a more effective source conditioning procedure as well as an improved Cs collar design. Initial results of tests employing a Cs collar with enhanced surface ionization geometry are also discussed.