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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Ionizing gas breakdown waves in strong electric fields.

A previous analysis by Albright and Tidman (1972) of the structure of an ionizing potential wave driven through a dense gas by a strong electric field is extended to include atomic structure details of the background atoms and radiative effects, especially, photoionization. It is found that photoionization plays an important role in avalanche propagation. Velocities, electron densities, and temperatures are presented as a function of electric field for both negative and positive breakdown waves in nitrogen.

Klingbeil, R.↗
NASA NTRS1994

Mass-loss rates, ionization fractions, shock velocities, and magnetic fields of stellar jets

In this paper we calculate emission-line ratios from a series of planar radiative shock models that cover a wide range of shock velocities, preshock densities, and magnetic fields. The models cover the initial conditions relevant to stellar jets, and we show how to estimate the ionization fractions and shock velocities in jets directly from observations of the strong emission lines in these flows. The ionization fractions in the HH 34, HH 47, and HH 111 jets are approximately 2%, considerably smaller than previous estimates, and the shock velocities are approximately 30 km/s. For each jet the ionization fractions were found from five different line ratios, and the estimates agree to within a factor of approximately 2. The scatter in the estimates of the shock velocities is also small (+/- 4 km/s). The low ionization fractions of stellar jets imply that the observed electron densities are much lower than the total densities, so the mass-loss rates in these flows are correspondingly higher (approximately greater than 2 x 10(exp -7) solar mass/yr). The mass-loss rates in jets are a significant fraction (1%-10%) of the disk accretion rates onto young stellar objects that drive the outflows. The momentum and energy supplied by the visible portion of a typical stellar jet are sufficient to drive a weak molecular outflow. Magnetic fields in stellar jets are difficult to measure because the line ratios from a radiative shock with a magnetic field resemble those of a lower velocity shock without a field. The observed line fluxes can in principle indicate the strength of the field if the geometry of the shocks in the jet is well known.

Hartigan, Patrick↗
NASA NTRS1985

Electrohydrodynamics

Models of electrohydrodynamic processes involving liquids with poorly ionized solutes at high (applied) field strengths were developed and tested. Extant theories which account for the details of physico-chemical processes associated with charged interfaces deal mainly with low field strengths and fully ionized solutes. The model used to describe processes at high field strengths--the leaky dielectric--omits consideration of electric double-layers, adsorption at interfaces, and chemical processes involved in the dissociation and recombination of solute species. Thus, even though the model depicts some features associated with bulk fluid motion, it fails to give a comprehensive picture. One example of the shortcomings of both the classical model of eletrokinetics at low field strengths and the leaky-dielectric model for high field strengths is found in the field strength dependence of the mobility of small particles in apolar liquids. The research will provide a more general model of electrohydrodynamic phenomena capable of application in diverse circumstances.

Saville, D. A.↗
NASA NTRS2005

Progress on the Plasmoid Thruster Experiment (PTX)

A plasmoid, also called a compact toroid, is a compact plasma structure with an integral magnetic field, that may be categorized according to the relative strength of the poloidal and toroidal magnetic field (Bp and Bt, respectively). An object with Bp/Bt much greater than 1 is called a Field Reverse Configuration (FRC); if Bp = Bt, it is called a Spheromak. The plasmoid thruster is a pulsed inductive device which operates by repetitively producing plasmoids that are accelerated and ejected at high velocity. As the process is inductive, this thruster avoids the problem of electrode erosion. Also, the magnetic structure of the plasmoid should suppress thermal and mass losses to the wall, and improve detachment of the plasma exhaust from the thruster. This concept should be capable of producing an Isp of 5,000 seconds and greater, with thrust densities of order 10(exp 5) N/sq m. The plasmoid thruster consists chiefly of a conical theta-pinch coil. Propellant is introduced onto a bias magnetic field, produced by an auxiliary coil, and is then pre-ionized, freezing in the magnetic field. The theta-pinch coil is then energized producing a field aligned anti- parallel to the bias field. The reversed field reconnects with the bias field to form the plasmoid. The magnetic pressure of the reversed field accelerates the plasmoid out of the thruster . A series of experiments have been conducted on the PTX device, which consisted of a single turn conical theta-pinch coil, driven by a 560 nF, 35 kV capacitor bank, which rang at a frequency of 500 kHz, and served all three functions required for formation: pre-ionization, bias field loading, and field reversal. Initial ionization was found to occur in an annular region at the exit plane of the coil, and was found to be reproducible with a variety of gases, including H2, D2, Ar, and an H2/N2 mixture (75% / 25%). A fast gas valve for injecting propellant has been tested, as well as a ringing pre-ionization circuit (operating at 5 Mhz) to better control the plasmoid formation. Velocities as high as 20 km/s have been measured for a plasmoid propagating into a static back-fill of neutral gas. Magnetic field and density measurements indicate that the plasmoid retains its structure well into the down-stream exhaust region, and that it is capable of pushing a dense cloud of neutral gas in front of it. Further experiments will focus on the effects of coil geometry and bias-field strength on the performance of the device. A high-power solid-state switching system is being developed in order to replace the spark-gap switch.

Martin, Adam↗
NASA NTRS2006

Miniature Free-Space Electrostatic Ion Thrusters

A miniature electrostatic ion thruster is proposed for maneuvering small spacecraft. In a thruster based on this concept, one or more propellant gases would be introduced into an ionizer based on the same principles as those of the device described in an earlier article, "Miniature Bipolar Electrostatic Ion Thruster". On the front side, positive ions leaving an ionizer element would be accelerated to high momentum by an electric field between the ionizer and an accelerator grid around the periphery of the concave laminate structure. On the front side, electrons leaving an ionizer element would be ejected into free space by a smaller accelerating field. The equality of the ion and electron currents would eliminate the need for an additional electron- or ion-emitting device to keep the spacecraft charge-neutral. In a thruster design consisting of multiple membrane ionizers in a thin laminate structure with a peripheral accelerator grid, the direction of thrust could then be controlled (without need for moving parts in the thruster) by regulating the supply of gas to specific ionizer.

Hartley, Frank T.↗
DOE OSTI2022

Electric field distribution in a non-self-sustained RF discharge with ionization generated by Ns discharge pulses

Abstract Electric field in a capacitively coupled, non-self-sustained RF discharge nitrogen plasma with external ionization generated by high-voltage ns pulses has been measured by ps Electric field induced second harmonic generation (EFISH). The measurements are made both in the bulk of the plasma and in the sheaths, using the absolute calibration by the Laplacian field between two plane electrodes. The results are compared with the kinetic modeling calculations. The RF electric field in the sheaths is significantly higher compared to that in the plasma, due to the displacement of the electrons by the drift oscillations and the resultant plasma self-shielding. However, the kinetic modeling predictions indicate that the electron impact ionization in the sheaths is largely ineffective, due to the low electron density. The reduction of the electric field in the plasma by the self-shielding in the sheaths is moderate, such that the energy is coupled to the plasma by the below-breakdown RF field. The peak RF field in the plasma is in the range of 15–25 Td, indicating the efficient vibrational excitation of N 2 by electron impact. The modeling predictions suggest that the targeted vibrational excitation of molecular species in a non-self-sustained RF discharge with external ionization is scalable to high pressures, electron densities, and discharge powers. The present approach can be extended to the vibrational excitation of other molecular species where the vibrational relaxation is relatively slow, such as CO, CO 2 , and H 2 .

Physics↗
NASA NTRS1963

NON-THERMAL NOISE MEASUREMENTS NEAR PLANETS

Measurements of cosmic noise, solar and jovian noise bursts, atmospheric noise and whistlers and vlf emissions, for the study of planetary ionization and magnetic fields

WHISTLER↗
NASA NTRS1993

Gravitational instability of a rotating partially-ionized plasma carrying a uniform magnetic field with Hall effect

The problem of gravitational instability of an infinite homogeneous self-gravitating medium carrying a uniform magnetic field in the presence of Hall effect has been investigated to include the effect due to rotation. The dispersion relation has been obtained. It has been found that the Jeans's criterion for the instability remains unaffected even when the effect due to rotation is considered in the presence of Hall effect carrying a uniform magnetic.

Kumar, Vinod↗
NASA NTRS1996

Sprites as Luminous Columns of Ionization Produced by Quasi-Electrostatic Thundercloud Fields

Quasi-electrostatic (QE) fields which exist above thunderclouds after lightning discharges can lead to the formation of columnar channels of breakdown ionization and carrot-like vertical luminous structures with typical transverse dimension approximately 5-10 km spaning an altitude range from approximately 80 km to well below approximately 50 km. The carrot-like forms closely resemble those observed in sprites. Results indicate that the appearance of optical emissions can be significantly delayed in time (approx. 1-20 ms) with respect to the causative lightning discharge.

Pasko, V. P.↗
NASA NTRS1984

Measurements of the optical emission produced during the laboratory beam plasma discharge

Optical observations of a beam-plasma discharge (BPD) in the laboratory showed that the discharge remained confined to a diameter little more than double that of the beam for injection parallel to the magnetic field and approximately equal to that of the beam for injection at large pitch angles. The diameter was independent of beam current but varied linearly with beam velocity and inversely with magnetic field strength. The ionization rate inferred from the total emission of 3914 A, integrated over the radial extent of the beam, was proportional to the excess beam current above that requied for BPD ignition. The proportionality constant ( 12 + or - 2) x 10 to the 14th ions/cm s A was valid over a wide range of pressure and of magnetic field strength. Power loss to ionization in a 20 m path was estimated at up to 4 percent of the beam power. Evidence is presented for effective confinement of suprathermal electrons (parallel to B) by some unidentified process other than electrostatic confinement.

Hallinan, T. J.↗
NASA NTRS2006

Miniature Oxidizer Ionizer for a Fuel Cell

A proposed miniature device for ionizing the oxygen (or other oxidizing gas) in a fuel cell would consist mostly of a membrane ionizer using the same principles as those of the device described in the earlier article, Miniature Bipolar Electrostatic Ion Thruster (NPO-21057). The oxidizing gas would be completely ionized upon passage through the holes in the membrane ionizer. The resulting positively charged atoms or molecules of oxidizing gas could then, under the influence of the fringe fields of the ionizer, move toward the fuel-cell cathode that would be part of a membrane/electrode assembly comprising the cathode, a solid-electrolyte membrane, and an anode. The electro-oxidized state of the oxidizer atoms and molecules would enhance transfer of them through the cathode, thereby reducing the partial pressure of the oxidizer gas between the ionizer and the fuel-cell cathode, thereby, in turn, causing further inflow of oxidizer gas through the holes in the membrane ionizer. Optionally the ionizer could be maintained at a positive electric potential with respect to the cathode, in which case the resulting electric field would accelerate the ions toward the cathode.

Hartley, Frank↗
NASA NTRS1995

Theoretical study of hole initiated impact ionization in bulk silicon and GaAs using a wave-vector-dependent numerical transition rate formulation within an ensemble Monte Carlo calculation

In this paper, calculations of the hole initiated interband impact ionization rate in bulk silicon and GaAs are presented based on an ensemble Monte Carlo simulation with the inclusion of a wave-vector-dependent numerical transition rate formulation. The ionization transition rate is determined for each of the three valence bands, heavy, light, and split-off, using Fermi's golden rule with a two-body, screened Coulomb interaction. The dielectric function used within the calculation is assumed to be wave-vector-dependent. Calculations of the field-dependent impact ionization rate as well as the quantum yield are presented. It is found from both the quantum yield results and examination of the hole distribution function that the effective threshold energy for hole initiated impact ionization is relatively soft, similar to that predicted for the corresponding electron initiated ionization events occur more frequently than either heavy or split-offf initiated ionization events in bulk silicon over the applied electric field strengths examined here, 250-500 kV/cm. Conversely,in GaAs, the vast majority of hole initated ionization events originate from holes within the split-off band.

Oguzman, Ismail H.↗
NASA NTRS1992

Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

Maloney, Philip↗