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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Surface plasma source with saddle antenna radio frequency plasma generator

A prototype RF H{sup -} 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{sup -} 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.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Hollow target magnetron-sputter-type solid material ion source

A thin-walled aluminum (Al) hollow electrode has been inserted into an ion source to serve as an electrode for a radio frequency magnetron discharge. The produced plasma stabilized by argon (Ar) gas sputters the Al electrode to form a beam of Al{sup +} and Ar{sup +} ions. The total beam current extracted through a 3 mm diameter extraction hole has been 50 {mu}A, with the Al{sup +} ion beam occupying 30% of the total beam current.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Influence of discharge gap on the discharge stability in a short vacuum arc ion source

The influence of the discharge gap between cathode and anode on the discharge stability in a short vacuum arc (SVA) ion source is presented in this paper. Planar cathode and cylindrical hollow anode made of titanium are investigated. There is a great need in present accelerator injection research for SVA source to produce the small deviation of the ion current beam. Current research shows that increasing the short discharge gap can reduce the level of ion current deviation and ion charge deviation from 29% and 31% to 15% and 17%, respectively. A microplasma plume generation mechanism in SVA and scanning electron microscopic results can be used to explain this interesting phenomenon.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Shunting arc plasma source for pure carbon ion beam

A plasma source is developed using a coaxial shunting arc plasma gun to extract a pure carbon ion beam. The pure carbon ion beam is a new type of deposition system for diamond and other carbon materials. Our plasma device generates pure carbon plasma from solid-state carbon material without using a hydrocarbon gas such as methane gas, and the plasma does not contain any hydrogen. The ion saturation current of the discharge measured by a double probe is about 0.2 mA/mm{sup 2} at the peak of the pulse.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Radio frequency discharge with control of plasma potential distribution

A RF discharge plasma generator with additional electrodes for independent control of plasma potential distribution is proposed. With positive biasing of this ring electrode relative end flanges and longitudinal magnetic field a confinement of fast electrons in the discharge will be improved for reliable triggering of pulsed RF discharge at low gas density and rate of ion generation will be enhanced. In the proposed discharge combination, the electron energy is enhanced by RF field and the fast electron confinement is improved by enhanced positive plasma potential which improves the efficiency of plasma generation significantly. This combination creates a synergetic effect with a significantly improving the plasma generation performance at low gas density. The discharge parameters can be optimized for enhance plasma generation with acceptable electrode sputtering.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Glow-to-arc transition events in H{sub 2}-Ar direct current pulsed plasma: Automated measurement of current and voltage

The glow-to-arc transition phenomena (arcing) observed in plasma reactors used in materials processing was studied through the arcs characteristic current and voltage waveforms. In order to capture these arcs signals, a LABVIEW based automated instrumentation system (ARCVIEW) was developed, including the integration of an oscilloscope equipped with proper current and voltage probes. The system also allows capturing the process parameters at the arc occurrence moments, which were used to map the arcs events conditions. Experiments in H{sub 2}-Ar DC pulsed plasma returned signals data from 215 arcs events, which were analyzed through software routines. According to the results, an anti-arcing system should react in the time order of few microseconds to prevent most of the damage caused by the undesired arcing phenomena.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Characteristic of a triple-cathode vacuum arc plasma source

In order to generate a better ion beam, a triple-cathode vacuum arc plasma source has been developed. Three plasma generators in the vacuum arc plasma source are equally located on a circle. Each generator initiated by means of a high-voltage breakdown between the cathode and the anode could be operated separately or simultaneously. The arc plasma expands from the cathode spot region in vacuum. In order to study the behaviors of expanding plasma plume generated in the vacuum arc plasma source, a Langmuir probe array is employed to measure the saturated ion current of the vacuum arc plasma source. The time-dependence profiles of the saturated current density of the triple vacuum arc plasma source operated separately and simultaneously are given. Furthermore, the plasma characteristic of this vacuum arc plasma source is also presented in the paper.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Optimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma

We have demonstrated an efficient extreme ultraviolet (EUV) source at 6.7 nm by irradiating Gd targets with 0.8 and 1.06 {mu}m laser pulses of 140 fs to 10 ns duration. Maximum conversion efficiency of 0.4% was observed within a 0.6% bandwidth. A Faraday cup observed ion yield and time of flight signals for ions from plasmas generated by each laser. Ion kinetic energy was lower for shorter pulse durations, which yielded higher electron temperatures required for efficient EUV emission, due to higher laser intensity. Picosecond laser pulses were found to be the best suited to 6.7 nm EUV source generation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Enhancement of ion generation in femtosecond ultraintense laser-foil interactions by defocusing

A simple method to enhance ion generation with femtosecond ultraintense lasers is demonstrated experimentally by defocusing laser beams on target surface. When the laser is optimally defocused, we find that the population of medium and low energy protons from ultra-thin foils is increased significantly while the proton cutoff energy is almost unchanged. In this way, the total proton yield can be enhanced by more than 1 order, even though the peak laser intensity drops. The depression of the amplified spontaneous emission (ASE) effect and the population increase of moderate-energy electrons are believed to be the main reasons for the effective enhancement.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Characterizing counter-streaming interpenetrating plasmas relevant to astrophysical collisionless shocks

A series of Omega experiments have produced and characterized high velocity counter-streaming plasma flows relevant for the creation of collisionless shocks. Single and double CH{sub 2} foils have been irradiated with a laser intensity of {approx} 10{sup 16} W/cm{sup 2}. The laser ablated plasma was characterized 4 mm from the foil surface using Thomson scattering. A peak plasma flow velocity of 2000 km/s, an electron temperature of {approx} 110 eV, an ion temperature of {approx} 30 eV, and a density of {approx} 10{sup 18} cm{sup -3} were measured in the single foil configuration. Significant increases in electron and ion temperatures were seen in the double foil geometry. The measured single foil plasma conditions were used to calculate the ion skin depth, c/{omega}{sub pi}{approx}0.16 mm, the interaction length, Script-Small-L {sub int}, of {approx} 8 mm, and the Coulomb mean free path, {lambda}{sub mfp}{approx}27mm. With c/{omega}{sub pi} Much-Less-Than Script-Small-L {sub int} Much-Less-Than {lambda}{sub mfp}, we are in a regime where collisionless shock formation is possible.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

The effect of viewing angle on the spectral behavior of a Gd plasma source near 6.7 nm

We have demonstrated the effect of viewing angle on the extreme ultraviolet (EUV) emission spectra of gadolinium (Gd) near 6.7 nm. The spectra are shown to have a strong dependence on viewing angle when produced with a laser pulse duration of 10 ns, which may be attributed to absorption by low ion stages of Gd and an angular variation in the ion distribution. Absorption effects are less pronounced at a 150-ps pulse duration due to reduced opacity resulting from plasma expansion. Thus for evaluating source intensity, it is necessary to allow for variation with both viewing angle and target orientation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Resonant planar antenna as an inductive plasma source

A resonant planar antenna as an inductive plasma source operating at 13.56 MHz inside a low pressure vacuum vessel is presented for potential plasma processing applications. Its principle consists in interconnecting elementary resonant meshes composed of inductive and capacitive elements. Due to its structure, the antenna shows a set of resonant modes associated with peaks of the real input impedance. Each of these modes is defined by its own current and voltage distribution oscillating at the frequency of the mode. A rectangular antenna of 0.55mx0.20m has been built, and first results obtained with argon plasmas are presented. Plasma generation is shown to be efficient as densities up to 4{center_dot}10{sup 17}m{sup -3} at 2000 W have been measured by microwave interferometry at a distance of 4 cm from the source plane. It is also demonstrated that the plasma couples inductively with the resonating currents flowing in the antenna above a threshold power of about 60 W. A non-uniformity of less than {+-}5% is obtained at 1000 W at a few centimeters above the antenna over 75% of its surface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Laser produced plasma for efficient extreme ultraviolet light sources

Extreme ultraviolet emission from laser produced plasma and their relevance to EUV source development is discussed. The current state of the field for Sn LPP sources operating at 13.5 nm is described and initial results are given for EUV emission from CO{sub 2} laser irradiation of a bulk Sn target. A maximum conversion efficiency of 1.7% has been measured and the influence of the CO{sub 2} laser temporal profile on the CE is discussed. A double pulse irradiation scheme is shown to increase CE up to a maximum value of 2.1% for an optimum prepulse - pulse delay of 150 ns. The emergence of a new EUVL source wavelength at 6.7 nm based on Gd and Tb LPPs has been outlined. An initial experiment investigating picosecond laser irradiation as a means to produce strong 6.7 nm emission from a Gd{sub 2}O{sub 3} target has been performed and verified.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

A new technique for X-ray spectroscopy of laser-plasmas with simultaneous 2D spatial resolution over a broad spectral range

Over the past few years, a new X-ray diagnostic technique has been developed by the group of the Intense Laser Irradiation Laboratory of the CNR in Pisa. Here we give a brief description of this new diagnostic tool, which basically allows X-ray spectroscopy of laser-produced plasmas to be performed over a broad photon energy range with a simultaneous 2D spatial resolution. An outline of recent results will be also given in order to assess the diagnostic capabilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Spatio-temporal mapping of ablated species in ultrafast laser-produced graphite plasmas

We studied the spatial and temporal distributions of ionic, neutral, and molecular species generated by femtosecond laser produced plasma under varying ambient nitrogen gas pressures. Plasmas were generated by irradiating planar graphite targets using 40 fs pulses of 800 nm radiation from a Ti:Sapphire laser. The results show that in the presence of an ambient gas, the molecular species spatial extension and lifetime are directly correlated to the evolution of excited ions. The present studies also provide valuable insights into the evolution history of various species and their excitation during ultrafast laser ablation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Streaked x-ray spectrometer having a discrete selection of Bragg geometries for Omega

The streaked x-ray spectrometer (SXS) is used with streak cameras [D. H. Kalantar, P. M. Bell, R. L. Costa, B. A. Hammel, O. L. Landen, T. J. Orzechowski, J. D. Hares, and A. K. L. Dymoke-Bradshaw, in 22nd International Congress on High-Speed Photography and Photonics, edited by D. L. Paisley and A. M. Frank (SPIE, Bellingham, WA, 1997), Vol. 2869, p. 680] positioned with a ten-inch manipulator on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] and OMEGA EP [L. J. Waxer et al., Presented at CLEO/QELS 2008, San Jose, CA, 4-9 May 2008 (Paper JThB1)] for time-resolved, x-ray spectroscopy of laser-produced plasmas in the 1.4- to 20-keV photon-energy range. These experiments require measuring a portion of this photon-energy range to monitor a particular emission or absorption feature of interest. The SXS relies on a pinned mechanical reference system to create a discrete set of Bragg reflection geometries for a variety of crystals. A wide selection of spectral windows is achieved accurately and efficiently using this technique. It replaces the previous spectrometer designs that had a continuous Bragg angle adjustment and required a tedious alignment calibration procedure. The number of spectral windows needed for the SXS was determined by studying the spectral ranges selected by OMEGA users over the last decade. These selections are easily configured in the SXS using one of the 25 discrete Bragg reflection geometries and one of the six types of Bragg crystals, including two curved crystals.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Suppression of drift waves in a linear magnetized plasma column

In magnetically confined fusion plasmas, drift wave driven turbulence can lead to enhanced particle transport from the plasma. Because of this, a significant research emphasis has been placed on the suppression of drift waves in the plasma edge. However, the combination of the toroidal geometry and short plasma lifetimes can make it difficult to fully characterize the properties of these instabilities. Because linear magnetized plasma devices offer a combination of simpler geometry and steady state plasma generation, it is possible to perform detailed studies of many types of plasma instabilities-including drift waves. This paper reports on a recent experiment in which low frequency instabilities ({omega} {<=} {omega}{sub ci}) in the Auburn Linear EXperiment for Instability Studies plasma device were characterized as drift waves and through changes in the parallel current, it is shown that it is possible to suppress these instabilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Femtosecond laser induced breakdown for combustion diagnostics

The focused beam of a 100 fs, 800 nm laser is used to induce a spark in some laminar premixed air-methane flames operating with variable fuel content (equivalence ratio). The analysis of the light escaping from the plasma revealed that the Balmer hydrogen lines, H{sub {alpha}} and H{sub {beta}}, and some molecular origin emissions were the most prominent spectral features, while the CN ({Beta}{sup 2}{Sigma}{sup +}-{Chi}{sup 2}{Sigma}{sup +}) band intensity was found to depend linearly with methane content, suggesting that femtosecond laser induced breakdown spectroscopy can be a useful tool for the in-situ determination and local mapping of fuel content in hydrocarbon-air combustible mixtures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗