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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The effects of magnetic nozzle configurations on plasma thrusters

Magnetoplasmadynamics (MPD) arc devices have been operated at power levels from 10 KW to 0.1 MW. When these devices have magnetic fields applied to them, they show marked increases in thrust in direct proportion to the magnitide of the applied field. Electrode erosion may be influenced by applied fields. This proposal will study the application of variable magnetic fields over a range of thruster powers, gas densities, and thruster configurations. It is proposed to examine this behavior with numerical codes and limited but relevant experimental tests.

York, Thomas M.↗
NASA NTRS2015

Proof-of-Concept Experiments on a Gallium-Based Ignitron for Pulsed Power Applications

Ignitrons are electrical switching devices that operate at switching times that are on the order of microseconds, can conduct high currents of thousands of amps, and are capable of holding off tens of thousands of volts between pulses. They consist of a liquid metal pool within an evacuated tube that serves both the cathode and the source of atoms and electrons for an arc discharge. Facing the liquid metal pool is an anode suspended above the cathode, with a smaller ignitor electrode tip located just above the surface of the cathode. The ignitron can be charged to significant voltages, with a potential difference of thousands of volts between anode and cathode. When an ignition pulse is delivered from the ignitor electrode to the cathode, a small amount of the liquid metal is vaporized and subsequently ionized, with the high voltage between the anode and cathode causing the gas to bridge the gap between the two electrodes. The electrons and ions move rapidly towards the anode and cathode, respectively, with the ions liberating still more atoms from the liquid metal cathode surface as a high-current plasma arc discharge is rapidly established. This arc continues in a self-sustaining fashion until the potential difference between the anode and cathode drops below some critical value. Ignitrons have been used in a variety of pulsed power applications, including the railroad industry, industrial chemical processing, and high-power arc welding. In addition, they might prove useful in terrestrial power grid applications, serving as high-current fault switches, quickly shunting dangerous high-current or high-voltage spikes safely to ground. The motivation for this work stemmed from the fact that high-power, high-reliability, pulsed power devices like the ignitron have been used for ground testing in-space pulsed electric thruster technologies, and the continued use of ignitrons could prove advantageous to the future development and testing of such thrusters. Previous ignitron designs have used mercury as the liquid metal cathode, owing to its presence as a liquid at room temperatures and a vapor pressure of 10 Pa (75 mtorr) at room temperature. While these are favorable properties, there are obvious environmental and personal safety concerns with the storage, handling, and use of mercury and its compounds. The purpose of the present work was to fabricate and test an ignitron that used as its cathode an alternate liquid metal that was safe to handle and store. To that end, an ignitron test article that used liquid gallium as the cathode material was developed and tested. Gallium is a metal that has a melting temperature of 29.76 C, which is slightly above room temperature, and a boiling point of over 2,300 C at atmospheric pressure. This property makes gallium the element with the largest relative difference between melting and boiling points. Gallium has a limited role in biology, and when ingested, it will be subsequently processed by the body and expelled rather than accumulating to toxic levels. The next section of this Technical Memorandum (TM) provides background information on the development of mercury-based ignitrons, which serves as the starting point for the development of the gallium-based variant. Afterwards, the experimental hardware and setup used in proof-of-concept testing of a basic gallium ignitron are presented. Experimental data, consisting of discharge voltage and current waveforms as well as high-speed imaging of the gallium arc discharge in the gallium ignitron test article, are presented to demonstrate the efficacy of the concept. Discussion of the data and suggestions on improvements for future iterations of the design are presented in the final two sections of this TM.

Ali, H. K.↗
NASA NTRS1995

Swirl Ring Improves Performance Of Welding Torch

Plasma-arc welding torch modified to create vortex in plasma gas to focus arc into narrower and denser column. Swirl ring contains four channels with angled exit holes to force gas to swirl as it flows out of torch past tip of electrode. Degradation of electrode and orifice more uniform and need to rotate torch during operation to compensate for asymmetry in arc reduced or eliminated. Used in both keyhole and nonkeyhole welding modes.

Mcgee, William F.↗
NASA NTRS1997

On the Development of a Magnetically Vectored Variable ISP Plasma Rocket

The development of a Magnetically Vectored Variable I(sub sp) Plasma Rocket at the Advanced Space Propulsion Laboratory (ASPL) is in progress at NASA's Johnson Space Center. The facility is using a small, 3.2 m tandem mirror device to study the application of RF heated magnetically contained plasmas for space propulsion. The central cell radius is 0.1 m and fields of 0.2 T and 2 T are possible in the central and end-cell mirror sections, respectively. A magnetoplasmadynamic (MPD) injector has just been acquired and will be used along with other methods of plasma refueling. A 1 MW magnet power supply upgrade is being developed with full implementation by the Spring of 1997. Two microwave systems for discharge initiation and plasma heating at 2.45 GHz and 14.0 GHz, respectively, are in operation. Additionally, RF systems with 200 kW and 1 MW of power are being modified and conditioned for operation. The concept provides electrode-less operation and variable thrush'specific impulse at constant power (200 -30 N /5000-30,000 seconds at 10 MW with a 60% efficiency). Optimization for speed or payload are possible with the same engine, giving the rocket great flexibility. Missions to Mars in 90 days are described, and missions to Pluto are under study.

Feliciano, Enectali Figueroa↗
NASA NTRS2002

Controlling Electron Backstreaming Phenomena Through the Use of a Transverse Magnetic Field

DEEP-SPACE mission propulsion requirements can be satisfied by the use of high specific impulse systems such as ion thrusters. For such missions. however. the ion thruster will be required to provide thrust for long periods of time. To meet the long operation time and high-propellant throughput requirements, thruster lifetime must be increased. In general, potential ion thruster failure mechanisms associated with long-duration thrusting can be grouped into four areas: (1) ion optics failure; (2) discharge cathode failure; (3) neutralizer failure; and (4) electron backstreaming caused by accelerator grid aperture enlargement brought on by accelerator grid erosion. The work presented here focuses on electron backstreaming. which occurs when the potential at the center of an accelerator grid aperture is insufficient to prevent the backflow of electrons into the ion thruster. The likelihood of this occurring depends on ion source operation time. plasma density, and grid voltages, as accelerator grid apertures enlarge as a result of erosion. Electrons that enter the gap between the high-voltage screen and accelerator grids are accelerated to the energies approximately equal to the beam voltage. This energetic electron beam (typically higher than 1 kV) can damage not only the ion source discharge cathode assembly. but also any of the discharge surfaces upstream of the ion acceleration optics that the electrons happen to impact. Indeed. past backstreaming studies have shown that near the backstreaming limit, which corresponds to the absolute value of the accelerator grid voltage below which electrons can backflow into the thruster, there is a rather sharp rise in temperature at structures such as the cathode keeper electrode. In this respect operation at accelerator grid voltages near the backstreaming limit is avoided. Generally speaking, electron backstreaming is prevented by operating the accelerator grid at a sufficiently negative voltage to ensure a sufficiently negative aperture center potential. This approach can provide the necessary margin assuming an expected aperture enlargement. Operation at very negative accelerator grid voltages, however, enhances ion charge-exchange and direct impingement erosion of the accelerator grid. The focus of the work presented here is the mitigation of electron backstreaming by the use of a magnetic field. The presence of a magnetic field oriented perpendicular to the thruster axis can significantly decrease the magnitude of the backflowing electron current by significantly reducing the electron diffusion coefficient. Negative ion sources utilize this principle to reduce the fraction of electrons in the negative ion beam. The focus of these efforts has been on the attenuation of electron current diffusing from the discharge plasma into the negative ion extraction optics by placing the transverse magnetic field upstream of the extraction electrodes. In contrast. in the case of positive ion sources such as ion thrusters, the approach taken in the work presented here is to apply the transverse field downstream of the ion extraction system so as to prevent electrons from flowing back into the source. It was found in the work presented here that the magnetic field also reduces the absolute value of the electron backstreaming limit voltage. In this respect. the applied transverse magnetic field provides two mechanisms for electron backstreaming mitigation: (1) electron current attenuation and (2) backstreaming limit voltage shift. Such a shift to less negative voltages can lead to reduced accelerator grid erosion rates.

Foster, John E.↗
NASA NTRS1971

A fixed bias, floating double probe technique with simple Langmuir probe characteristics

A new floating double-probe method is presented which has advantages over other floated-probe systems previously described in literature. The method utilized two electrodes, one of constant area and the other with a variable area. The two-electrode configuration is separated by a fixed bias voltage. The current-voltage characteristics of the new technique, which are generated by varying the area of the one electrode, are identical to those of a simple Langmuir probe, thus coupling all the advantages of a floated-probe system with the simple analysis scheme generally applied to the Langmuir probe for the determination of plasma density and temperature.

Szuszczewicz, E. P.↗
NASA NTRS1972

Fixed-bias floating double-probe technique with simple Langmuir-probe characteristics.

A new floating double-probe method is presented which has advantages over other floated-probe systems heretofore described in the literature. The method utilizes two electrodes, one of constant area and the other with a variable area, and the two-electrode configuration is separated by a fixed bias voltage. The current-voltage characteristics of the new technique, which are generated by varying the area of one electrode, are identical to those of a simple Langmuir probe, thus coupling all the advantages of a floated-probe system with the simple analysis scheme generally applied to the Langmuir probe for the determination of plasma density and temperature.

Szuszczewicz, E. P.↗
NASA NTRS1986

Textured carbon surfaces on copper by sputtering

A very thin layer of highly textured carbon is applied to a copper surface by a triode sputtering process. A carbon target and a copper substrate are simultaneously exposed to an argon plasma in a vacuum chamber. The resulting carbon surface is characterized by a dense, random array of needle like spires or peaks which extend perpendicularly from the copper surface. The coated copper is especially useful for electrode plates in multistage depressed collectors.

Curren, A. N.↗
DOE OSTI2024

Novel One-Step Production of Carbon-Coated Sn Nanoparticles for High-Capacity Anodes in Lithium-Ion Batteries

Lithium-ion batteries offer the highest energy density of any currently available portable energy storage technology. By using different anode materials, these batteries could have an even greater energy density. One material, tin, has a theoretical lithium capacity (994 mAh/g) over three-times higher than commercial carbon anode materials. Unfortunately, to achieve this high capacity, bulk tin undergoes a large volume expansion, and the material pulverizes during cycling, giving a rapid capacity fade. To mitigate this issue, tin must be scaled down to the nano-level to take advantage of unique micromechanics at the nanoscale. Synthesis techniques for Sn nanoparticle anodes are costly and overly complicated for commercial production. A novel one-step process for producing carbon-coated Sn nanoparticles via spark plasma erosion (SPE) shows great promise as a simple, inexpensive production method. The SPE method, characterization of the resulting particles, and their high-capacity reversible electrochemical performance as anodes are described. With only a 10% addition of these novel SPE carbon-coated Sn particles, one anode composition demonstrated a reversible capacity of ~460 mAh/g, achieving the theoretical capacity of that particular electrode formulation. These SPE carbon-coated Sn nanoparticles are drop-in ready for present commercial lithium-ion anode processing and would provide a ~10% increase in the total capacity of current commercial lithium-ion cells.

25 ENERGY STORAGE↗
DOE OSTI2025

Optical interferometry of high-energy nanosecond pin-to-pin discharges in atmospheric air

This paper describes the construction and application of an optical-frequency Michelson interferometer for measuring electron number density within high-energy, high-power nanosecond pin-to-pin discharges (>10 mJ pulse energy, >1 MW pulse power). A 21 mJ, 11 ns spark across a 3 mm pin-to-pin electrode gap was analyzed at 7 ns into the discharge to demonstrate the operation of the interferometer. A peak electron density of 2.3 × 10 17 cm −3 was observed at these conditions, and it was consistent with estimates of plasma channel resistance based on V–I measurements. This initial work paves the way for a larger parametric study of the spatial and temporal dynamics of electron number density in nanosecond pin-do-pin discharges under various conditions.

electron number density↗
DOE OSTI2026

A tetrahedral probe constellation approach for measuring canonical momentum in self-organized laboratory plasma

To examine momentum redistribution processes and study generalized helicities during plasma relaxation in Madison Symmetric Torus, MST, reversed field pinch plasma, a new probe is being tested to measure the full 3D plasma ion flow and magnetic field vectors at four spatial locations arranged in a tetrahedral shape reminiscent of a satellite measurement constellation. These measurements permit calculation of ∇ x $\vec{u}$ and canonical momentum, where $\vec{u}$ is the plasma ion flow vector. The probe consists of four probe heads arranged in a tetrahedral pattern, with an overall probe diameter of ∼31.75 mm. The probe head diameter is ∼1.0 cm, which is of the order of the ion Larmor radius. Each head has four molybdenum electrodes, also arranged in tetrahedral geometry, which are biased relative to a common return electrode, using four power supplies (one for each head), to measure the local ion flow. Additionally, each head has three orthogonal magnetic pickup coils within it to measure equilibrium and fluctuating magnetic fields.

Physics - Plasma physics↗
DOE OSTI2024

Plasma pressure profiles in a sheared-flow-stabilized Z-pinch

We report the plasma pressure reached inside the central plasma column of a sheared-flow-stabilized Z-pinch using Thomson scattering measurements. Building on previously reported experimental results and the analysis methods established for the high temperature and moderate density plasmas generated on the FuZE device, we show evidence of a central plasma region with higher electron temperature and density, which is consistent with a pinch behavior. Elevated electron temperatures up to 2.25 ± 0.8 keV and densities up to (4.9±0.2)×1017 cm−3 are observed to temporally coincide with the fusion neutron production from the plasma. Reconstructed plasma pressure profiles highlight the presence of a several millimeter-wide column with elevated pressure whose location varies shot-to-shot. The plasma pressure rises as neutron production from the deuterium plasma increases, reaching a peak value of 2.6 kBar. This peak value is consistent with a radially force-balanced pinch equilibrium model based on the measured ∼320 kA pinch current. Complete datasets were obtained at two axial locations, 10 and 20 cm axial position from the tip of the central electrode, which corroborate the estimated neutron source axial lengths.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1976

Characteristics of the NASA Lewis bumpy torus plasma generated with high positive or negative applied potentials

The toroidal ring of plasma contained in the NASA Lewis bumpy-torus superconducting magnet facility may be biased to positive or negative potentials approaching 50 kilovolts by applying direct-current voltages of the respective polarity to 12 or fewer of the midplane electrode rings. The electric fields which are responsible for heating the ions by E/B drift then point radially outward or inward. The low-frequency fluctuations below the ion cyclotron frequency appeared to be dominated by rotating spokes.

Roth, J. R.↗
DOE OSTI2024

Overview of the recent experimental research on the J-TEXT tokamak

The J-TEXT capability is enhanced compared to two years ago with several upgrades of its diagnostics and the increase of electron cyclotron resonance heating (ECRH) power to 1 MW. With the application of electron cyclotron wave (ECW), the ECW assisted plasma startup is achieved; the tearing mode is suppressed; the toroidal injection of 300 kW ECW drives around 24 kA current; fast electrons are generated with toroidal injected ECW and the runaway current conversion efficiency increases with ECRH power. The mode coupling between 2/1 and 3/1 modes are extensively studied. The coupled 2/1 and 3/1 modes usually lead to major disruption. Their coupling can be either suppressed or avoided by external resonant magnetic perturbation fields and hence avoids the major disruption. It is also found that the 2/1 threshold of external field is significantly reduced by a pre-excited 3/1 mode, which can be either a locked island or an external kink mode. The disruption control is studied by developing prediction methods capable of cross tokamak application and by new mitigation methods, such as the biased electrode or electromagnetic pellet injector. The high-density operation and related disruptions are studied from various aspects. Approaching the density limit, the collapse of the edge shear layer is observed and such collapse can be prevented by applying edge biasing, leading to an increased density limit. The density limit is also observed to increase, if the plasma is operated in the poloidal divertor configuration or the plasma purity is increased by increasing the pre-filled gas pressure or ECRH power during the start-up phase.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1975

Laboratory plasma probe studies

Diagnostic experiments performed in a collisionless plasma using CO2 as the working gas are described. In particular, simultaneous measurements that have been performed by means of Langmuir- and RF-probes are presented. A resonance occurring above the parallel resonance in the frequency characteristic of a two electrode system is interpreted as being due to the resonant excitation of electroacoustic waves.

Heikkila, W. J.↗
NASA NTRS1991

Plasma-Arc Torch For Welding Ducts In Place

Plasma-arc-welding torch redesigned, more suitable for applications in which moved in circular or other orbits about stationary cylindrical workpieces. Preserves elements of original design critical to performance and endurance, but modifies other elements to decrease overall size of torch. Electrode collet and collet nut installed and removed through hole in top; makes installation and removal easier.

Gangl, Kenneth J.↗
NASA NTRS2003

Review of the High Performance Antiproton Trap (HiPAT) Experiment

Many space propulsion concepts exist that use matter-antimatter reactions. Current antiproton production rates are enough to conduct proof-of-principle evaluation of these concepts. One enabling technology for such experiments is portable storage of low energy antiprotons, to transport antiprotons to experimental facilities. To address this need, HiPAT is being developed, with a design goal of containing 10(exp 12) particles for up to 18 days. HiPAT is a Penning-Malmberg trap with a 4 Tesla superconductor, 20kV electrodes, radio frequency (RF) network, and 10(exp -13) Torr vacuum. 'Normal' matter is being used to evaluate the system. An electron beam ionizes background gas in situ, and particle beams are captured dynamically. The experiment examines ion storage lifetimes, RF plasma diagnostics, charge exchange with background gases, and dynamic ion beam capture.

Martin, James J.↗