H- radio frequency source development at the Spallation Neutron Source

Journal Article · Sun Jan 01 04:00:00 EST 2012 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.3678651· OSTI ID:1045243

Welton, Robert F ^[1]; Pennisi, Terry R ^[1]; Roseberry, Ron T ^[1]; Stockli, Martin P ^[1]

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1. ORNL

The Spallation Neutron Source (SNS) now routinely operates nearly 1 MW of beam power on target with a highly persistent {approx}38 mA peak current in the linac and an availability of {approx}90%. H{sup -} beam pulses ({approx}1 ms, 60 Hz) are produced by a Cs-enhanced, multicusp ion source closely coupled with an electrostatic low energy beam transport (LEBT), which focuses the 65 kV beam into a radio frequency quadrupole accelerator. The source plasma is generated by RF excitation (2 MHz, {approx}60 kW) of a copper antenna that has been encased with a thickness of {approx}0.7 mm of porcelain enamel and immersed into the plasma chamber. The ion source and LEBT normally have a combined availability of {approx}99%. Recent increases in duty-factor and RF power have made antenna failures a leading cause of downtime. This report first identifies the physical mechanism of antenna failure from a statistical inspection of {approx}75 antennas which ran at the SNS, scanning electron microscopy studies of antenna surface, and cross sectional cuts and analysis of calorimetric heating measurements. Failure mitigation efforts are then described which include modifying the antenna geometry and our acceptance/installation criteria. Progress and status of the development of the SNS external antenna source, a long-term solution to the internal antenna problem, are then discussed. Currently, this source is capable of delivering comparable beam currents to the baseline source to the SNS and, an earlier version, has briefly demonstrated unanalyzed currents up to {approx}100 mA (1 ms, 60 Hz) on the test stand. In particular, this paper discusses plasma ignition (dc and RF plasma guns), antenna reliability, magnet overheating, and insufficient beam persistence.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: ORNL other overhead
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1045243
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 2 Vol. 83; ISSN 0034-6748; ISSN RSINAK
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
ANTENNAS
BEAM CURRENTS
BEAM TRANSPORT
COPPER
ELECTROSTATICS
ENAMELS
EXCITATION
GEOMETRY
HEATING
IGNITION
ION SOURCES
LINEAR ACCELERATORS
MITIGATION
NEUTRON SOURCES
PLASMA
PORCELAIN
QUADRUPOLE LINACS
SCANNING ELECTRON MICROSCOPY
SPALLATION
TARGETS