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Spallation Neutron Source ramps to higher power levels that can be sustained with high availability. The goal is 1.4MWdespite a compromised radio frequency quadrupole (RFQ), which requires higher radio frequency power than design levels to approach the nominal beam transmission. Unfortunately at higher power the RFQ often loses its thermal stability, a problem apparently enhanced by beam losses and high influxes of hydrogen. Delivering as much H- beam as possible with the least amount of hydrogen led to plasma outages. The root cause is the dense 1-ms long ~55-kW 2-MHz plasma pulses reflecting ~90% of the continuous ~300 W, 13-MHz power, which was mitigated with a 4-ms filter for the reflected power signal and an outage resistant, slightly detuned 13-MHz match. Lowering the H2 gas also increased the H- beam current to ~55 mA and increased the RFQ transmission by ~7% (relative). [ABSTRACT FROM AUTHOR]

Existing RF ion sources for accelerators have specific efficiencies for H+ and H- ion generation ~3-5 mA/cm2 kW, where about 50 kW of RF power is typically needed for 50 mA beam current production. The Saddle Antenna (SA) surface plasma source (SPS) described here was developed to improve H- ion production efficiency, reliability, and availability. In SA RF ion source, the efficiency of positive ion generation in the plasma has been improved to 200 mA/cm2 kW. After cesiation, the current of negative ions to the collector was increased from 1 mA to 10 mA with RF power ~1.5 kW in the plasma (6 mm diameter emission aperture) and up to 30 mA with ~4 kW RF. Continuous wave (CW) operation of the SA SPS has been tested on the test stand. The general design of the CW SA SPS is based on the pulsed version. Some modifications were made to improve the cooling and cesiation stability. CW operation with negative ion extraction was tested with RF power up to ~1.2 kW in the plasma with production up to Ic = 7 mA. A stable long time generation of H- beam without degradation was demonstrated in RF discharge with AlN discharge chamber. [ABSTRACT FROM AUTHOR]

Extraction of negative ions from a saddle antenna radio-frequency surface plasma source is considered. Several versions of new plasma generators with different antennas and magnetic field configurations were tested in the small Oak Ridge National Laboratory Spallation Neutron Source Test Stand. The efficiency of positive ion generation in plasma has been improved to 200 mA/cm² kW from 2.5 mA/cm² kW. A small oven was developed for cesiation by cesium compounds and alloy decomposition. After cesiation, a current of negative ions to the collector was increased from 1 mA to 10 mA with 1.5 kW RF power in the plasma and longitudinal magnetic field B1 ~ 250 G. The specific efficiency of H- production was increased to 20 mA/cm² kW from 2.5 mA/cm² kW. [ABSTRACT FROM AUTHOR]

A prototype RF H- surface plasma source (SPS) with saddle (SA) RF antenna is developed which will provide better power efficiency for high pulsed and average current, higher brightness with longer lifetime and higher reliability. Several versions of new plasma generators with small AlN discharge chambers and different antennas and magnetic field configurations were tested in the plasma source test stand. A prototype SA SPS was installed in the Spallation Neutron Source (SNS) ion source test stand with a larger, normal-sized SNS AlN chamber that achieved unanalyzed peak currents of up to 67 mA with an apparent efficiency up to 1.6 mA/kW. Control experiments with H- beam produced by SNS SPS with internal and external antennas were conducted. A new version of the RF triggering plasma gun has been designed. A saddle antenna SPS with water cooling is fabricated for high duty factor testing. [ABSTRACT FROM AUTHOR]