High-current, High-duty-factor Experiments with the H Ion Source for the Spallation Neutron Source

The ion source for the 1 MW Spallation Neutron Source (SNS) is required to provide 35 mA of H beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance less than 0.15 π mm mrad. The H beam will be accelerated to 65 keV and matched into a 2.5 MeV RFQ. The ion source is expected to ultimately produce 70 mA of H at 6% duty factor when the SNS is upgraded to 2 MW of power. For this application, a radio-frequency driven, magnetically filtered multicusp source is being developed at Berkeley Lab. The design of this new ion source is directed towards operation at the required high duty factor. Experimental results of the ion source operated in pure volume production mode (without cesium) and in hybrid mode (with cesium released into the source) are compared. An improved cesium dispensing system will be presented. 1 ION SOURCE DESIGN A schematic of the SNS R&D #1 H ion source [1] is shown in figure 1. The ion source is mounted inside a reentrant cylinder to move the ion source into the vacuum vessel. This enhances the vacuum pumping of the extraction gap. The source plasma chamber (10-cm-long by 10-cm-diam.) is made out of a copper cylinder with a back plate at one end and an outlet electrode at the other end. The plasma is confined by the longitudinal line-cusp fields produced by 20 rows of water-cooled, samariumcobalt magnets that surround the source chamber and transverse magnets on the back flange. The hydrogen plasma is produced inductively by up to 65 kW of pulsed 2 MHz RF power. RF coupling is accomplished via a 2 1/2-turn, porcelain-coated (watercooled copper tubing) antenna connected to a matching network that matches the impedances of RF amplifier and Figure 1: Schematic view of SNS R&D #1 H ion source. Work supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contr. No. DE-AC03-76SF00098. # Email: [email protected] 0-7803-5573-3/99/$10.00@1999 IEEE. 1911 Proceedings of the 1999 Particle Accelerator Conference, New York, 1999