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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Current collection by high voltage anodes in near ionospheric conditions

The authors experimentally identified three distinct regimes with large differences in current collection in the presence of neutrals and weak magnetic fields. In magnetic field/anode voltage space the three regions are separated by very sharp transition boundaries. The authors performed a series of laboratory experiments to study the dependence of the region boundaries on several parameters, such as the ambient neutral density, plasma density, magnetic field strength, applied anode voltage, voltage pulsewidth, chamber material, chamber size and anode radius. The three observed regimes are: classical magnetic field limited collection; stable medium current toroidal discharge; and large scale, high current space glow discharge. There is as much as several orders of magnitude of difference in the amount of collected current upon any boundary crossing, particularly if one enters the space glow regime. They measured some of the properties of the plasma generated by the breakdown that is present in regimes II and III in the vicinity of the anode including the sheath modified electrostatic potential, I-V characteristics at high voltage as well as the local plasma density.

Antoniades, John A.↗
NASA NTRS2000

The Interaction of Solar wind Discontinuities with the Earth's Bow Shock

Funding from NASA Grant No. NAG54679 was received in three installments. The first year's installment amounted to only one month of salary support and was used to prepare survey plots. The second year's installment allowed us to complete two research papers concerning the interaction of solar wind discontinuities with the Earth's bow shock. In the first (published) paper, we reported that the discontinuities launch slow mode waves into the magnetosheath and the slow mode waves always propagate antisunward through the flank magnetosheath. Because the sunward/antisunward sense of the magnetosheath magnetic field reverses across local noon, so does the (north/south or east/west) sense of the velocity fluctuations associated with the waves. Wind, Geotail, and IMP-8 observations were used for this study. In the second study, we used Wind and Interball-1 observations to demonstrate that pressure pulses in the magnetosheath occur in pairs and that they bound pressure cavities and/or brief intervals of outward magnetopause motion. This paper is now in press. Funding from the third year's installment has been used to investigate the two aspects of the foreshock. Two manuscripts are now in preparation for submission to the Journal of Geophysical Research. The first reports that waves within the foreshock account for many instances of poor correlations between two solar wind monitors. Remaining cases of poor correlation occur during intervals of nearly constant IMF orientations and magnetic field strengths. While the former category pose a significant difficulty for space weather forecasts, the latter do not. The second study surveys IMP-8 observations of the foreshock. We find that diamagnetic cavities are common, particularly during periods of high solar wind velocity and low solar wind density. Plasma densities, temperatures, and magnetic field strengths fall during intervals of enhanced energetic particle fluxes. The cavities are bounded by regions of decelerated solar wind plasma and enhanced densities and magnetic field strengths.

Sibeck, David G.↗
NASA NTRS1998

Measurements of the Plasma Parameters and Low Frequency Oscillations in the Fisk Plasma Source

A new plasma device, the Fisk Plasma Source (FPS), has been developed at Fisk University. This plasma device is used to study the physics of low temperature plasmas and plasma-material interactions. The FPS device is a stainless steel vacuum 6-way cross vacuum vessel with at 10-inch inner diameter. Low temperature argon plasmas are generated using DC glow discharge and thermionic filament techniques. Spatial profiles of the plasma density, plasma potential, and electron temperature are measured using Langmuir probes. We present initial experimental measurements of density and temperature profiles in the FPS device. Experimental and theoretical studies of low frequency oscillations observed in the FPS device are also presented.

Thomas, Edward, Jr.↗
DOE OSTI2025

Excitation of whistler and slow-X waves by runaway electrons in a collisional plasma

Runaway electrons are known to provide robust ideal or collisionless kinetic drive for plasma wave instabilities in both the whistler and slow-X branches, via the anomalous Doppler-shifted cyclotron resonances. In a cold and dense post-thermal-quench plasma, collisional damping of the plasma waves can compete with the collisionless drive. Previous studies have found that, due to their higher wavelength and frequency, slow-X waves suffer stronger collisional damping than the whistlers, while the ideal growth rate of slow-X modes is higher. Here, we study runaway avalanche distributions that maintain the same eigen distribution and increase only in magnitude over time. The distributions are computed from the relativistic Fokker–Planck–Boltzmann solver, upon which a linear dispersion analysis is performed to search for the most unstable or least damped slow-X and whistler modes. Taking into account the effect of plasma density, plasma temperature, and effective charge number, we find that the slow-X modes tend to be excited before the whistlers in a runaway current ramp-up. Furthermore, even when the runaway current density is sufficiently high that both branches are excited, the most unstable slow-X mode has a much higher growth rate than the most unstable whistler mode. The qualitative and quantitative trends uncovered in the current study indicate that even though past experiments and modeling efforts have concentrated on whistler modes, there is a compelling case that slow-X modes should also be a key area of focus in the runaway self-mediation through wave instabilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1976

Plasma research in electric propulsion at Colorado State University

The effect of electron bombardment ion thruster magnetic field configurations on the uniformity of the plasma density and the ion beam current density are discussed. The optimum configuration is a right circular cylinder which has significant fields at its outer radii and one end but is nearly field free within the cylinder and at the extraction grid end. The production and loss of the doubly charged ions which effect sputtering damage within thrusters are modeled and the model is verified for the mercury propellant case. Electron bombardment of singly charged ions is found to be the dominant double ion production mechanism. The low density plasma (approx. one million elec/cubic centimeter which exists in the region outside of the beam of thrust producing ions which are drawn from the discharge chamber is discussed. This plasma is modeled by assuming the ions contained in it are generated by a charge exchange process in the ion beam itself. The theoretical predictions of this model are shown to agree with experimental measurements.

Wilbur, P. J.↗
NASA NTRS1979

Computer modeling of events in the inner magnetosphere

The first effort at computer simulating the behavior of the inner magnetosphere during a substorm-type event on 19 September 1976 was completed. The computer model simulates many aspects of the behavior of the closed-field-line portion of the earth's magnetosphere, and the auroral and subauroral ionosphere. For these regions, the program self-consistently computes electric fields, electric currents, hot-plasma densities, plasma flow velocities and other parameters. Highlights of the results of our event simulation are presented. Predicted electric fields for several times during the event agree reasonably well with corresponding data from satellite S3-2. Detailed discussion is presented for a case of rapid subauroral flow that was observed on one S3-2 pass and is predicted by the computer runs. The computed global distribution of Birkeland current agrees reasonably well with the observations of Iijima and Potemra.

Harel, M.↗
NASA NTRS1981

Large-scale waves in the ionosphere observed by the AE satellite

Atmospheric Explorer (AE) satellite data were used to establish whether coherent waves in the gravity wave range are present in both neutral and ionized media in the thermosphere. The AE-C data in particular are shown. Data consist of the in situ argon, helium, nitrogen, and oxygen densities, plasma density, and ion and electron temperatures. Filtering provides the fluctuation signals for each which are spectrum analyzed for power and cross spectra. The observed frequencies are essentially proportional to the spatial wavenumbers along the satellite track. Scale sizes range from thousands to tens of kilometers.

Gross, S. H.↗
NASA NTRS1991

Particle dynamics and current-free double layers in an expanding, collisionless, two-electron-population plasma

The expansion of a two-electron-population, collisionless plasma into vacuum has been examined in detail. Plasma density, plasma potential, electric field, and particle disribution functions have been measured in situ. It is demonstrated that the presence of a low-pressure (P not less than 2 x 10 to the -5th torr) background neutral gas modifies the expansion of the plasma. A new plasma source creating dense, pulsed discharge plasma with a low background pressure (P not greater than 2 x 10 to the -6th torr) has been developed to perform in situ measurements of the temporal and spatial plasma evolution during its expansion into vacuum.

Hairapetian, G.↗
NASA NTRSDate not supplied

The Effect of Anode Configuration on the Plasma Plume of a 25-A class Hollow Cathode

The effect of anode configuration on the plasma plume properties of a 25-A class hollow cathode are experimentally characterized. At a nominal operating condition of 20.8 A and 14.7 sccm of xenon, the cathode was operated with two axially-segmented anodes of different diameters at varying distance from the cathode. A fast, reciprocating motion stage was used to rapidly insert an ion saturation probe and an emissive probe on cathode centerline, and from those measurements, spatial profiles of plasma density, plasma potential, and electron temperature were calculated. For both anode diameters, maximum plasma potential and electron temperature increased with increasing anode distance. However, the 64-mm diameter anode was found to be significantly more sensitive to position, with measurements indicating that parameters changed continuously with position instead of an instantaneous mode change at a certain critical distance. The 254-mm diameter, in contrast, showed much more similar plasma property profiles across the range of anode positions tested and much smaller changes per unit increase in distance. These results are discussed in the context of assessing anode design for component-level cathode tests.

Space propulsion↗