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The Spallation Neutron Source (SNS) now routinely operates near 1 MW of beam power on target with 30-40 mA peak current in the linac and an overall availability of ∼90%. H- beam pulses (∼1 ms, 60Hz) are produced by a RF-driven, Cs-enhanced, multi-cusp ion source closely coupled to an electrostatic Low Energy Beam Transport (LEBT) which focuses the beam into an RFQ accelerator. The ion source and LEBT normally have a combined availability of ∼99%. The source plasma is generated by RF excitation (2MHz, ∼60kW) of a copper antenna which has been encased with a thickness of ∼0.7 mm of porcelain enamel and is immersed into the plasma chamber. Failure of this coating material during operations has been a long-standing problem and a cause of downtime. This report describes new antenna installation criteria which have led to trouble free antenna performance over this last year, a significant improvement over previous years. These results suggest that inclusions and defects in the antenna coating play an important role in the failure process. This report also addresses the problem of inconsistent performance among our inventory of five ostensibly identical baseline SNS ion sources. Over the last several years only source [sharp/mesh/hash_synonym]3 has regularly provided the required beam current to the SNS by outperforming the others by 5-10 mA. To address this, all baseline sources have been characterized on the ion source test stand and small physical differences between source [sharp/mesh/hash_synonym]3 and the others have been identified and the impact of those differences on beam production assessed. [ABSTRACT FROM AUTHOR]

This paper describes the accomplishments of the SNS H- ion source, which delivers routinely ∼50 mA at a 5.4% duty factor with ∼99% availability, enabling 1 MW beams for neutron production with ∼90% availability. It discusses the need for increasing reliability and beam current. But mostly it focuses on its unexpected feature: H- beams that are apparently persistent for up to 5 weeks without adding Cs after an initial dose of less than ∼5 mg. Thermal emission and sputtering are qualitatively evaluated, and appear consistent with a negligible Cs sputter rate after the initial dose disappears from the Cs plasma. It concludes with a list of future experiments that can shed more light on this apparently unique Cs cycle. [ABSTRACT FROM AUTHOR]

The Spallation Neutron Source (SNS) now routinely operates near 1 MW of beam power on target with a highly-persistent ∼38 mA peak current in the linac and an availability of ∼90%. The ∼1 ms-long, 60 Hz, ∼50 mA H- beam pulses are extracted from a Cs-enhanced, multi-cusp, RF-driven, internal-antenna ion source. An electrostatic LEBT (Low Energy Beam Transport) focuses the 65 kV beam into the RFQ accelerator. The ion source and LEBT have normally a combined availability of ∼99%. Although much progress has been made over the last years to achieve this level of availability further improvements are desirable. Failures of the internal antenna and occasionally impaired electron dump insulators require several source replacements per year. An attempt to overcome the antenna issues with an AlN external antenna source early in 2009 had to be terminated due to availability issues. This report provides a comprehensive review of the design, experimental history, status, and description of recently updated components and future plans for this ion source. The mechanical design for improved electron dump vacuum feedthroughs is also presented, which is compatible with the baseline and both external antenna ion sources. [ABSTRACT FROM AUTHOR]

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory reached 1-MW of beam power in September 2009, and now routinely operates near 1-MW for the production of neutrons. This paper reviews the performance, operational issues, implemented and planned mitigations of the SNS H- ion source to support such high power-level beams with high availability. Some results from R&D activities are also briefly described. [ABSTRACT FROM AUTHOR]