RESUMO
Factors limiting operating lifetime of a Compact Surface Plasma Sources (CSPS) are analyzed and possible treatments for lifetime enhancement are considered. Increased cooling permeate increased discharge power and increased beam intensity and duty factor. A design of an advanced CSPS with geometrical focusing of H(-) flux is presented.
RESUMO
Existing RF ion sources for accelerators have specific efficiencies for H(+) and H(-) ion generation â¼3-5 mA/cm(2) 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/cm(2) kW. After cesiation, the current of negative ions to the collector was increased from 1 mA to 10 mA with RF power â¼1.5 kW in the plasma (6 mm diameter emission aperture) and up to 30 mA with â¼4 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 â¼1.2 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.
RESUMO
The Oak Ridge National Laboratory operates the Spallation Neutron Source, consisting of a H(-) ion source, a 1 GeV linac and an accumulator ring. The accumulated <1 µs-long, â¼35 A beam pulses are extracted from the ring at 60 Hz and directed onto a liquid Hg target. Spalled neutrons are directed to â¼20 world class instruments. Currently, the facility operates routinely with â¼1.2 MW of average beam power, which soon will be raised to 1.4 MW. A future upgrade with a second target station calls for raising the power to 2.8 MW. This paper describes the status of two accelerator components expected to play important roles in achieving these goals: a recently acquired RFQ accelerator and the external antenna ion source. Currently, the RFQ is being conditioned in a newly constructed 2.5 MeV Integrated Test Facility (ITF) and the external antenna source is also being tested on a separate test stand. This paper presents the results of experiments and the testing of these systems.
RESUMO
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 smal Oak Ridge National Laboratory Spallation Neutron Source Test Stand. The efficiency of positive ion generation in plasma has been improved to 200 mA/cm(2) kW from 2.5 mA/cm(2) 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 Bl â¼ 250 G. The specific efficiency of H(-) production was increased to 20 mA/cm(2) kW from 2.5 mA/cm(2) kW.
RESUMO
The Spallation Neutron Source (SNS), a large scale neutron production facility, routinely operates with 30-40 mA peak current in the linac. Recent measurements have shown that our RF-driven internal antenna, Cs-enhanced, multi-cusp ion sources injects â¼55 mA of H(-) beam current (â¼1 ms, 60 Hz) at 65-kV into a Radio Frequency Quadrupole (RFQ) accelerator through a closely coupled electrostatic Low-Energy Beam Transport system. Over the last several years a decrease in RFQ transmission and issues with internal antennas has stimulated source development at the SNS both for the internal and external antenna ion sources. This report discusses progress in improving internal antenna reliability, H(-) yield improvements which resulted from modifications to the outlet aperture assembly (applicable to both internal and external antenna sources) and studies made of the long standing problem of beam persistence with the external antenna source. The current status of the external antenna ion source will also be presented.
RESUMO
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.
RESUMO
The Spallation Neutron Source (SNS) now routinely operates nearly 1 MW of beam power on target with a highly persistent â¼38 mA peak current in the linac and an availability of â¼90%. H(-) beam pulses (â¼1 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, â¼60 kW) of a copper antenna that has been encased with a thickness of â¼0.7 mm of porcelain enamel and immersed into the plasma chamber. The ion source and LEBT normally have a combined availability of â¼99%. 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 â¼75 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 â¼100 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.
RESUMO
The problem of a vertical load acting on a tooth model under strong fixation of the root is investigated by the method of finite elements. The regions of the tooth fracture are determined. The changes of the tooth stress state caused by bone resorption are analyzed.