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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
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↗
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↗
NASA NTRS2006

Ion Thruster Discharge Performance Per Magnetic Field Topography

DC-ION is a detailed computational model for predicting the plasma characteristics of rain-cusp ion thrusters. The advanced magnetic field meshing algorithm used by DC-ION allows precise treatment of the secondary electron flow. This capability allows self-consistent estimates of plasma potential that improves the overall consistency of the results of the discharge model described in Reference [refJPC05mod1]. Plasma potential estimates allow the model to predict the onset of plasma instabilities, and important shortcoming of the previous model for optimizing the design of discharge chambers. A magnetic field mesh simplifies the plasma flow calculations, for both the ions and the secondary electrons, and significantly reduces numerical diffusion that can occur with meshes not aligned with the magnetic field. Comparing the results of this model to experimental data shows that the behavior of the primary electrons, and the precise manner of their confinement, dictates the fundamental efficiency of ring-cusp. This correlation is evident in simulations of the conventionally sized NSTAR thruster (30 cm diameter) and the miniature MiXI thruster (3 cm diameter).

plasma processes↗
NASA NTRS1981

Comparison of theory and in situ observations for electron and ion distributions in the near wake of the Explorer 31 and AE-C satellites

Measurements of electron density, plasma potential, and mean ion mass from the Explorer 31 satellite, and measurements of ion current, plasma potential, and ion composition from the Atmosphere Explorer C satellite were used in a comparative study with Parker's theory regarding the charged particle distribution in the near wake of an ionospheric satellite (1976). It is shown that theory and experiment agree fairly well in the angle-of-attack range between 90 and 135 deg. In the maximum rarefaction zone (between 145 and 180 deg), however, the theoretical model overestimates the measured ion depletion by several orders of magnitude. A comparison between theory and the Explorer 31 electron measurements shows that the theory again overestimates the electron depletion. These discrepancies are mainly due to the use of a steady-state theory and a single ion equation (using a mean ion mass). Improved agreement between theory and experiment can be obtained by the use of the time-dependent Vlasov-Poisson equations with separate equations for the various ion species.

Samir, U.↗
NASA NTRS2003

Testing and Analysis of NEXT Ion Engine Discharge Cathode Assembly Wear

Experimental and analytical investigations were conducted to predict the wear of the discharge cathode keeper in the NASA Evolutionary Xenon Thruster. The ion current to the keeper was found to be highly dependent upon the beam current, and the average beam current density was nearly identical to that of the NSTAR thruster for comparable beam current density. The ion current distribution was highly peaked toward the keeper orifice. A deterministic wear assessment predicted keeper orifice erosion to the same diameter as the cathode tube after processing 375 kg of xenon. A rough estimate of discharge cathode assembly life limit due to sputtering indicated that the current design exceeds the qualification goal of 405 kg. Probabilistic wear analysis showed that the plasma potential and the sputter yield contributed most to the uncertainty in the wear assessment. It was recommended that fundamental experimental and modeling efforts focus on accurately describing the plasma potential and the sputtering yield.

Domonkos, Matthew T.↗
NASA NTRS2019

Near Field Probe Measurements in the Plume of a NEXT Ion Thruster

Due to the extremely long lifetime and ground testing complications, such as facility backpressure effects, modeling is a necessary tool for validating mission lifetime requirements. Both NASA's Glenn Research Center and Jet Propulsion Laboratory have developed lifetime validation models for the NEXT ion thruster. The largest uncertainties in these models are due to unknown plasma properties, such as plasma potential, that occur very near to the grid. Previous studies have made measurements in the mid to far field. Here, we make very near field measurements of the plasma properties in the ion beam within 0.1 thruster radii of the grid using various probes. Emissive and triple Langmuir probes are swept through the plume to spatially resolve plasma potential, electron temperature and ion density very near to the grid. The goal is to provide refined inputs to the lifetime modeling efforts and increase the accuracy of the models.

Arthur, Neil↗
NASA NTRS2019

Near Field Probe Measurements in the Plume of a NEXT Ion Thruster

Due to the extremely long lifetime and ground testing complications, such as facility backpressure effects, modeling is a necessary tool for validating mission lifetime requirements. Both NASA's Glenn Research Center and Jet Propulsion Laboratory have developed lifetime validation models for the NEXT ion thruster. The largest uncertaintiesin these models are due to unknown plasma properties, such as fields plasma potential, that occur very near to the grid. Previous studies have made measurements in the mid to far field. Here, we make very near field measurements of the plasma properties in the ion beam within 0.1 thruster radii of the grid using various probes. Emissive and triple Lang-muir probes are swept through the plume to spatially resolve plasma potential, electron temperature and ion density very near to the grid. The goal is to provide refined inputs to the lifetime modeling efforts and increase the accuracy of the models.

Arthur, Neil A.↗
NASA NTRS1988

Temporal evolution of collisionless sheaths

Experimental measurements have been performed to determine the temporal evolution of Langmuir sheaths near an electrode to which a negative step bias is applied in a collisionless argon plasma. The plasma was produced by a hot-filament discharge in a multidipole device. Plasma potential data were obtained using emissive probes with two different techniques: time-resolved sampling and time-averaged techniques. The sheath is found to initially form close to the electrode, to extend to a maximum separation, and to contract to a steady-state value. The time scale required to reach a steady state is close to the time scale of the presheath relaxation. Characteristics of sheaths in RF plasmas are also measured using a parallel-plate plasma capacitor. It is observed that the plasma potential profile has significant variation with frequency, even for frequencies as low as 1 kHz which are far below the ion plasma frequency (about 1 MHz).

Cho, M. H.↗
NASA NTRS1992

A first-principles model for orificed hollow cathode operation

A theoretical model describing orificed hollow cathode discharge is presented. The approach adopted is based on a purely analytical formulation founded on first principles. The present model predicts the emission surface temperature and plasma properties such as electron temperature, number densities and plasma potential. In general, good agreements between theory and experiment are obtained. Comparison of the results with the available related experimental data shows a maximum difference of 10 percent in emission surface temperature, 20 percent in electron temperature and 35 percent in plasma potential. In case of the variation of the electron number density with the discharge current a maximum discrepancy of 36 percent is obtained. However, in the case of the variation with the cathode internal pressure, the predicted electron number density is higher than the experimental data by a maximum factor of 2.

Salhi, A.↗
NASA NTRS1984

Experimental observations of self-similar plasma expansion

The present investigation is concerned with measurements of the plasma potential profile of an expanding plasma, taking into account the demonstration of the self-similar behavior of such a plasma. The obtained experimental results are consistent with self-similar solutions reported by Crow et al. (1975). It is found that the quasi-neutrality condition breaks down early during the experiment. A consideration of the effect of charge separation is, therefore, required. Attention is given to the evolution of the potential profiles of the expanding plasma as a function of time, the accelerated ion fronts, and the sheath formation of the expanding plasma into a floating boundary.

Chan, C.↗
NASA NTRS1979

Neutralization tests on the SERT 2 spacecraft

Neutralization test data obtained on the SERT 2 spacecraft are presented. Tests included ion beam neutralization of a thruster by a close (normal design) neutralizer as well as by a distant (1 meter) neutralizer. Parameters affecting neutralization, such as neutralizer bias voltage, neutralizer anode voltage, local spacecraft plasma density, and solar array voltage configuration were varied and changes in plasma potentials were measured. A plasma model is presented as an approximation of observed results.

Kerslake, W. R.↗
NASA NTRS1992

The potential for plasma diagnostics from stellar extreme-ultraviolet observations

A description of the lines from the most abundant ions in the EUV spectrum in the range 50-500 A that have special diagnostic significance is presented. These lines are from plasmas in the temperature range from 10 exp 5 to 10 exp 7 K. Their utility for determining temperature, density, and abundances is demonstrated. An objective grating spectrometer, based on the Skylab slitless spectrograph, for making celestial observations in the EUV spectral region with high spectral resolution is also described. Such an instrument, if equipped with a multilayer grating, can achieve efficiencies over limited EUV wavelength ranges that rival much larger telescope-spectrometer instruments for the observation of stars and other celestial objects.

Feldman, U.↗
NASA NTRS1995

Overview of the effects of neutral gas releases on high-voltage sounding rocket platforms

Four recent sounding rocket experiments demonstrate that the release of neutral gas from both positively and negatively charged vechicles returns the vehicle potential to near the plasma potential. Early active experiment payloads, CHARGE-2 and Space Power Experiments Aboard Rockets 1 (SPEAR-1) observed enhanced currents from/to the vehicles during unplanned attitude thruster firings. The follow-on CHARGE-2B ad SPEAR-3 payloads directly measured the changes to the vehicle potential caused by both planned argon and unplanned nitrogen releases. The gas releases from positively charged CHARGE-2B consistently reduced the potential to 20-50 V, wheras the gas releases from negatively charged SPEAR-3 brought the potential to between -200 and -500 V. The difference in grounding levels for positively and negatively charged payloads suggests that the gas responsible for grounding is near the vehicle, within a small fraction of the sheath size.

Berg, G. A.↗
NASA NTRS2013

Radial Profiles of the Plasma Electron Characteristics in a 30 kW Arc Jet

The present effort aims to strengthen modeling work conducted at the NASA Ames Research Center by measuring the critical plasma electron characteristics within and slightly outside of an arc jet plasma column. These characteristics are intended to give physical insights while assisting in the formulation of boundary conditions to validate full scale simulations. Single and triple Langmuir probes have been used to achieve estimates of the electron temperature (T(sub e)), electron number density (n(sub e)) and plasma potential (outside of the plasma column) as probing location is varied radially from the flow centerline. Both the electron temperature and electron number density measurements show a large dependence on radial distance from the plasma column centerline with T(sub e) approx. = (3 - 12 eV and n(sub e) approx. = 10(exp 12) - 10(exp 14)/cu cm.

Codron, Douglas A.↗
NASA NTRS1981

Simulation of charge exchange plasma propagation near an ion thruster propelled spacecraft

A model describing the charge exchange plasma and its propagation is discussed, along with a computer code based on the model. The geometry of an idealized spacecraft having an ion thruster is outlined, with attention given to the assumptions used in modeling the ion beam. Also presented is the distribution function describing charge exchange production. The barometric equation is used in relating the variation in plasma potential to the variation in plasma density. The numerical methods and approximations employed in the calculations are discussed, and comparisons are made between the computer simulation and experimental data. An analytical solution of a simple configuration is also used in verifying the model.

Robinson, R. S.↗
NASA NTRS1982

A review of studies on ion thruster beam and charge-exchange plasmas

Various experimental and analytical studies of the primary beam and charge-exchange plasmas of ion thrusters are reviewed. The history of plasma beam research is recounted, emphasizing experiments on beam neutralization, expansion of the beam, and determination of beam parameters such as electron temperature, plasma density, and plasma potential. The development of modern electron bombardment ion thrusters is treated, detailing experimental results. Studies on charge-exchange plasma are discussed, showing results such as the relationship between neutralizer emission current and plasma beam potential, ion energies as a function of neutralizer bias, charge-exchange ion current collected by an axially moving Faraday cup-RPA for 8-cm and 30-cm ion thrusters, beam density and potential data from a 15-cm ion thruster, and charge-exchange ion flow around a 30-cm thruster. A 20-cm thruster electrical configuration is depicted and facility effects are discussed. Finally, plasma modeling is covered in detail for plasma beam and charge-exchange plasma.

Carruth, M. R., Jr.↗