ORNL, Oak Ridge, Tennessee
ORNL RAD, Oak Ridge, Tennessee
Funding: The work at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC, was performed under contract DE-AC05-00OR2275 for the US Department of Energy.
The U.S. Spallation Neutron Source (SNS) is an accelerator-based, pulsed neutron-scattering facility, currently in the process of ramping up neutron production. In order to insure that we will meet our operational commitments as well as provide for future facility upgrades with high reliability, we have developed an RF-driven, H- ion source based on a ceramic aluminum nitride (AlN) plasma chamber*. This source is expected to enter service as the SNS neutron production source starting in 2009. This report details the design of the production source which features an AlN plasma chamber, 2-layer external antenna, cooled-multicusp magnet array, Cs2CrO4 cesium system and a Molybdenum plasma ignition gun. Performance of the production source both on the SNS accelerator and SNS test stand is reported. The source has also been designed to accommodate an elemental Cs system with an external reservoir which has demonstrated unanalyzed beam currents up to ~100mA (60Hz, 1ms) on the SNS ion source test stand.
*R.F. Welton, et al., “Next Generation Ion Sources for the SNS”, Proceedings of the 1st Conference on Negative Ion Beams and Sources, Aix-en-Provence, France, 2008
ORNL RAD, Oak Ridge, Tennessee
ORNL, Oak Ridge, Tennessee
Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
Over the past year the performance of the LBNL H- source has been improved to routinely produce 36 mA when averaged over 0.7 ms long pulses at 60 Hz, measured at the RFQ output of the Spallation Neutron Source accelerator. This is up from 25-30 mA during early 2008, and up from {10}-20 mA during 2007. Some of the recent gain was achieved with refined conditioning and cesiation procedures, which now yield peak performance within 8 hours of starting a source change. The ~10 mg released Cs is sufficient for 3 weeks of operation without significant degradation. Another recent gain comes from the elevated Cs collar temperature, which was gradually implemented to probe its impact on the performance lifetime. In addition, load resistors improve the voltage stability of the electron dump and the lenses, which now can be more finely tuned. The achieved gain allowed for lowering the RF power to ~50 kW for improved reliability. A beam current of 38 mA is required at SNS for producing neutrons with a proton beam power of 1.4 MW. In one case, after 12 days of 4% duty factor operation, 56 mA were demonstrated with 60 kW of RF power. This is close to the 59 mA required for 3 MW operations.
ORNL, Oak Ridge, Tennessee
Funding: *SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
The new SNS Allison emittance scanner measures emittances of 65 kV ion beams over a range of ± 116 mrad. Its versatile control system allows for time-dependent emittance measurements synchronized by an external trigger, and therefore is suited for studying pulsed systems. After a programmable delay the system acquires a variable array of beam current measurements, each averaged over a changeable time span. The baseline of the current measurements are determined by averaging a fraction of 1 ms shortly before the start of the ion beam pulse. This paper presents the time evolution of emittance ellipses during the 1 ms H- beam pulses emerging from the SNS test LEBT, which is important for loss considerations. In addition it presents the time evolution of emittance ellipses during the 3 week active lifetime of an SNS H- source, which is an operational issue. Additional emittance data characterize the dependence on the electron-dump voltage, the extractor voltage, and the LEBT lens voltages, all of which were critical for reaching the 38 mA baseline H- beam current. Emittance data for the dependence on the beam current highlight the challenges for the SNS power upgrade.