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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

H{sup -} radio frequency source development at the Spallation Neutron Source

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.

43 PARTICLE ACCELERATORS↗
NASA NTRS1983

Detection of an extended soft X-ray source H 2326-79 in the southern sky

A new extended soft X-ray source H 2326-79 has been detected with the low energy detectors of the HEAO1 A-2 experiment. The source is found to have a size of approximately 2.5 arcsec and is centered at RA(1950)=23 h 26 m, Decl.(1950)= -79 deg 24 min. The observed energy flux, seen mainly in the 0.18-0.4 keV band, corrected for finite source size, is found to be about 2.6 x 10 to the -11th erg/sq cm-sec. It is determined that the source spectrum fits well with either an exponential model (gaunt factor included) or with a Raymond Smith plasma model. The observed characteristics of the source are studied for two physical models: a very old low surface brightness supernova remnant undetected in the radio and optical regions, and an enhanced X-ray emission region surrounding an H I cloud embedded in the hot cavity of Loop I. The observed source is also interpreted as a group of two or more unresolved stellar X-ray sources.

Agrawal, P. C.↗
DOE OSTI2017

Record Performance of and Extraction Studies with the Spallation Neutron Source H- Injector

During the past year the Spallation Neutron Source has operated with proton beam powers up to 1.4 MW with good availability. However, after a recent premature target failure the power was reduced to 1 MW for the ~20-week service cycle of the new target, whereas the subsequent target will be used at 1.2 MW. The ion source and low-energy beam transport deliver 50 to 60 mA H- beams into the RFQ with availbilities of ~99.5%. The compromised RFQ transmission limits the LINAC beam to ~35 mA, which is sufficient for 1.4 MW. Our current injector efforts focus on improving reliability and increasing the source service cycles beyond the achived 7 A·h to reduce the venting of the RFQ and to improve the stability of the accelerator operations. In addition, extraction studies show that higher extraction fields improve the RFQ transmission, apparently due to a reduced emittance of the LEBT H- beams.

Stockli, Martin P.↗
DOE OSTI2013

Recent Performance of the SNS H-Source for 1-MW Neutron Production

This paper describes the performance of the SNS ion source and LEBT as they continue to deliver ~50 mA H- beams at a 5.3% duty factor required for neutron production with a ~1MW proton beam since the fall of 2009. The source continues to deliver persistent H- beams for up to 6 weeks without adding Cs after an initial dose of ~4 mg, except when there are excessive plasma impurities. In one case the H- beam decayed due to an air leak, which is shown to be consistent with sputtering of the Cs layer, and which allows to bracket the plasma potential. In another case, the performance of two sources degraded progressively, which appears to be consistent with a progressive deterioration of the Cs covered Mo converter. These two and other recently discovered issues are discussed in detail.

Cesium↗
DOE OSTI2018

Optimization of the cesiation process for the spallation neutron source (SNS) H - ion sources

RF-driven (internal and external antenna), Cs-enhanced H - ion sources at the Spallation Neutron Source (SNS) facility are capable of producing high current (>60 mA), high duty-factor (1 ms, 60 Hz) H - beams lasting multiple months. A solid reaction Cs dispenser system is used to cesiate the ion source. This work reports on our continuous effort to optimize the ion source cesiation process guided by the Cs signal observed with the plasma emission spectroscopy to mitigate the Cs induced high voltage sparking while assuring to enable high H - beam currents

Han, Baoxi↗
DOE OSTI2014

Plasma emission spectroscopy for operating and developing the Spallation Neutron Source (SNS) H- ion sources

An RF-driven, Cs-enhanced H- ion source feeds the SNS accelerator with a high current (typically >50 mA), ~1.0 ms pulsed beam at 60 Hz. To achieve the persistent high current beam for several weeks long service cycles, each newly installed ion source undergoes a rigorous conditioning and cesiation processes. Plasma conditioning outgases the system and sputter-cleans the ion conversion surfaces. A cesiation process immediately following the plasma conditioning releases Cs to provide coverage on the ion conversion surfaces. The effectiveness of the ion source conditioning and cesiation is monitored with plasma emission spectroscopy using a high-sensitivity optical spectrometer. Plasma emission spectroscopy is also used to provide a mean for diagnosing and confirming a failure of the insulating coating of the ion source RF antenna which is immersed in the plasma. Emissions of composition elements of the antenna coating material, Na emission being the most significant, drastically elevate to signal a failure when it happens. Plasma spectra of the developmental ion source with an AlN chamber and an external RF antenna are also briefly discussed.

Han, Baoxi↗
DOE OSTI2015

Recent Performance and Ignition Tests of the pulsed SNS H- Source for 1-MW Neutron Production

After acquiring several reliable spare targets, SNS ramped the beam power from 850 kW to 1.4 MW, which required an increase in H- beam pulse length from 0.88 to 1.0 ms at 60 Hz. This increase initially produced slow 2-MHz power ramp-ups and, after several weeks of uninterrupted operation, it produced plasma outages every time the pulse length was raised above ~0.95 ms. Similar outages were previously observed towards the end of long service cycles, which were believed to indicate that the breakdown voltage of the high purity hydrogen started to exceed the induced electric fields. In 2011 the RF was reconfigured to start with 10 cycles of 1.96 MHz, which yielded the shortest H- beam rise times and apparently eliminated those plasma outages. The new, pulse-length dependent outages were eliminated by increasing the initial frequency to 1.985 MHz. However, careful frequency studies are unable to justify this frequency. In addition, the paper discusses the issues and solutions for the electron-dump voltage, which starts to sag and become unstable after several weeks of high current operation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Recent Performance of and Plasma Outage Studies with the SNS H- Source

SNS ramps to higher power levels that can be sustained with high availability. The goal is 1.4 MW despite a compromised RFQ, which requires higher RF 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 ~300W, 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 also increased the H- beam current to ~55 mA, and increased the transmission by ~7%.

H- ion source↗
DOE OSTI2014

Herschel observations of extra-ordinary sources: H{sub 2}S as a probe of dense gas and possibly hidden luminosity toward the Orion KL hot core

We present Herschel/HIFI observations of the light hydride H{sub 2}S obtained from the full spectral scan of the Orion Kleinmann-Low nebula (Orion KL) taken as part of the Herschel Observations of EXtra-Ordinary Sources GT (guaranteed time) key program. In total, we observe 52, 24, and 8 unblended or slightly blended features from H{sub 2} {sup 32}S, H{sub 2} {sup 34}S, and H{sub 2} {sup 33}S, respectively. We only analyze emission from the so-called hot core, but emission from the plateau, extended ridge, and/or compact ridge are also detected. Rotation diagrams for ortho and para H{sub 2}S follow straight lines given the uncertainties and yield T {sub rot} = 141 ± 12 K. This indicates H{sub 2}S is in local thermodynamic equilibrium and is well characterized by a single kinetic temperature or an intense far-IR radiation field is redistributing the population to produce the observed trend. We argue the latter scenario is more probable and find that the most highly excited states (E {sub up} ≳ 1000 K) are likely populated primarily by radiation pumping. We derive a column density, N {sub tot}(H{sub 2} {sup 32}S) = 9.5 ± 1.9 × 10{sup 17} cm{sup –2}, gas kinetic temperature, T {sub kin} = 120±{sub 10}{sup 13} K, and constrain the H{sub 2} volume density, n{sub H{sub 2}} ≳ 9 × 10 {sup 7} cm{sup –3}, for the H{sub 2}S emitting gas. These results point to an H{sub 2}S origin in markedly dense, heavily embedded gas, possibly in close proximity to a hidden self-luminous source (or sources), which are conceivably responsible for Orion KL's high luminosity. We also derive an H{sub 2}S ortho/para ratio of 1.7 ± 0.8 and set an upper limit for HDS/H{sub 2}S of <4.9 × 10 {sup –3}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Workshop on Performance Variations in H- Ion Sources 2012: PV H-12

This paper briefly summarizes a workshop held in Jyvaskyla the day after NIBS 12. The half-day workshop aimed at globally capturing the issue of performance variations in H- sources. There was a focus on production facilities and facilities that work under production like conditions, because there are often high expectations to be met.

cesium↗
DOE OSTI2014

Plasma emission spectroscopy for operating and developing the Spallation Neutron Source (SNS) H{sup −} ion sources

A RF-driven, Cs-enhanced H{sup −} ion source feeds the SNS accelerator with a high current (typically >50 mA), ∼1.0 ms pulsed beam at 60 Hz. To achieve the persistent high current beam for several weeks long service cycles, each newly installed ion source undergoes a rigorous conditioning and cesiation processes. Plasma conditioning outgases the system and sputter-cleans the ion conversion surfaces. A cesiation process immediately following the plasma conditioning releases Cs to provide coverage on the ion conversion surfaces. The effectiveness of the ion source conditioning and cesiation is monitored with plasma emission spectroscopy using a high-sensitivity optical spectrometer. Plasma emission spectroscopy is also used to provide a means for diagnosing and confirming a failure of the insulating coating of the ion source RF antenna which is immersed in the plasma. Emissions of composition elements of the antenna coating material, Na emission being the most significant, drastically elevate to signal a failure when it happens. Plasma spectra of the developmental ion source with an AlN (aluminum nitrite) chamber and an external RF antenna are also briefly discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

RF low-level control for the Linac4 H{sup −} source

The H{sup −} source for the Linac4 accelerator at CERN uses an RF driven plasma for the production of H{sup −}. The RF is supplied by a 2 MHz RF tube amplifier with a maximum power output of 100 kW and a pulse duration of up to 2 ms. The low-level RF signal generation and measurement system has been developed using standard CERN controls electronics in the VME form factor. The RF frequency and amplitude reference signals are generated using separate arbitrary waveform generator channels. The frequency and amplitude are both freely programmable over the duration of the RF pulse, which allows fine-tuning of the excitation. Measurements of the forward and reverse RF power signals are performed via directional couplers using high-speed digitizers, and permit the estimation of the plasma impedance and deposited power via an equivalent circuit model. The low-level RF hardware and software implementations are described, and experimental results obtained with the Linac4 ion sources in the test stand are presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Characterization of the CW starter plasma RF matching network for operating the SNS H{sup −} ion source with lower H{sub 2} flows

The Spallation Neutron Source H{sup −} ion source is operated with a pulsed 2-MHz RF (50-60 kW) to produce the 1-ms long, ∼50 mA H{sup −} beams at 60 Hz. A continuous low power (∼300 W) 13.56-MHz RF plasma, which is initially ignited with a H{sub 2} pressure bump, serves as starter plasma for the pulsed high power 2-MHz RF discharges. To reduce the risk of plasma outages at lower H{sub 2} flow rates which is desired for improved performance of the following radio frequency quadrupole, the 13.56-MHz RF matching network was characterized over a broad range of its two tuning capacitors. The H-α line intensity of the 13.56-MHz RF plasma and the reflected power of the 13.56-MHz RF were mapped against the capacitor settings. Optimal tunes for the maximum H-α intensity are consistent with the optimal tunes for minimum reflected power. Low limits of the H{sub 2} flow rate not causing plasma outages were explored within the range of the map. A tune region that allows lower H{sub 2} flow rate has been identified, which differs from the optimal tune for global minimum reflected power that was mostly used in the past.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗