First Results on the Path Towards a Microwave-Assisted H-Ion Source

A novel concept for creating intense beams of negative hydrogen ion beams is presented. In this approach, an ECR ion source operating at 2.45 GHz frequency is utilized as a primary plasma generator and coupled to an SNS-type multi-cusp H^-ion source. The secondary source is driven by chopped dc power, thereby avoiding the use of filaments or of an internal rf antenna. The development of the new ion source is aimed at supporting the future beam-power goal of 3 MW for the Spallation Neutron Source (SNS) accelerator systems that will be pursued after the start of SNS operations, but application to other proton driver accelerators that include an accumulator ring is feasible as well. The first three phases of this development effort have been successfully completed: assembly of a test stand and verification of the performance of an rf-driven SNS ion-source prototype; extraction of electrons up to 1.5 A current from a 2.45-GHz ECR ion source obtained on loan from Argonne National Laboratory; and creation of a plasma in the H^-discharge chamber with a pulsed discharge current of 12 A. The next goal is the demonstration of actual H^-ion production by this novel, hybrid ion source. This paper describes the source principle and design in detail and reports on the current status of the development work.