Initial tests of an elemental cs-system with the SNS ion source

The Spallation Neutron Source* (SNS) facility employs an RF-driven, Cs-enhanced, multi-cusp H- ion source. To date, the source has been successfully utilized in commissioning the SNS accelerator and in early operations of the facility, producing beam currents of 10- 40 mA with duty-factors of ~0.1 %. In the near future, the ion source will be required to inject 40-60 mA of beam current into the linac with a duty-factor of ~7%. We are therefore investigating methods to simultaneously increase the beam current, duty-factor and reliability of the SNS ion source. Presently, Cs is dispensed within the source using cartridges containing a compressed powder mixture of Cs ₂CrO₄, Al and Zr loaded into a cylindrical collar surrounding the outlet aperture. The source is cesiated by briefly increasing the temperature of the Cs₂CrO₄. Initially, this process increases the H- beam current significantly but the beam soon decays to a more modest level of enhancement. The degree and duration of H- beam current enhancement can vary considerably between ion sources (not reproducible) and can only be repeated 1-3 times in a given source before the Cs is depleted and the source needs to be replaced. This is especially problematic during high duty-factor operation. This report describes the design of an elemental Cs system incorporating an external elemental Cs reservoir (based on the proven Fermilab design), a directly heated Cs transfer line, a Cs injection collar and a temperaturecontrolled conical ionization surface. The results of the first experiments performed with this system are reported.