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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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Discussion of the improvements incorporated since 1969 in a low-power MPD thruster design which is considered a potential candidate for satellite station keeping and attitude control. The improvements include a new cathode design, and changes in thruster geometry, with xenon used as the propellant. A better thermal design is found to be necessary for further improvement of the thruster.
The characteristics of two low-frequency electrostatic flute instabilities of a low-pressure hollow cathode arc discharge are reported. Mode I has azimuthal mode number m = 1, and occurs when the radial electric field is negative (directed inward), while mode II has m = - 1 and occurs when the field is positive. The radial electric field is controlled by varying the potential of a secondary anode cylinder located close to the outer discharge radius. A linear perturbation analysis, based on the two-fluid equations, is given for a low-beta, collisionless, cylindrical plasma column, immersed in a uniform axial magnetic field, having a Gaussian density profile and an arbitrary radial electric field profile. Reasonable correlation between theory and experiment is demonstrated for both modes.
Voids forming at interface when copper is cast onto tungsten can be eliminated by adding wetting agent during casting process. Small amount of copper and nickel are cast onto thoriated tungsten insert, insert is recast with more copper to form electrode. Good thermal conductance results in long-lived cathode.
Cold cathode ionization gages were left on the lunar surface as part of ALSEP (Apollo Lunar Surface Experiment Package) on Apollo missions 12, 14, and 15. An instrument prepared for Apollo 13 did not reach the surface because of the abort of that mission. The gages that reached the lunar surface measured the amounts of gas present in the vicinity of the ALSEP sites. The observed daytime gas concentrations were initially about two orders of magnitude greater than the nighttime observations; this was due to contamination of the landing area by the Apollo operations and equipment, and the daytime measurements showed a decrease with time characterized by a time constant of a few months.
Thin-tip 0.3-cm-outside-diameter hollow-cathode neutralizers were used to investigate causes of neutralizer tip erosion experienced in thruster endurance tests. Bell-jar tests indicated that neutralizers with new rolled tantalum foil inserts coated with an emissive mixture eroded very little over the neutral flow rates investigated (3 to 10 mA) for simulated 5- and 8-cm-diameter thruster neutralizer conditions. Tip erosion rates of neutralizers operated with no insert or emissive mixture increased by two orders of magnitude for both configurations as the neutral flow rate decreased. Spectroscopic analysis of the discharge plasma from neutralizers operated with inserts coated with the emissive mixture detected tungsten at all neutral flow rates for both thruster neutralizer conditions. The only source of tungsten was the tip. Therefore, detection of tungsten indicated neutralizer tip erosion. Barium, an element of the emissive mixture, was detected at low neutral flow rates for the 5-cm-diameter thruster neutralizer operating condition only.
Hollow cathode configurations with cavity diameters up to 2 cm have been operated in quasi-steady MPD discharges at tens of kA and argon massflows up to 16 g per sec. Internal probe measurements exhibit densities of current attachment of 1.5 kA per sq cm in a 1 cm wide zone at the end of the cavity coincident with low electric fields of less than 10 V per cm. This zone is further characterized by a sheath of bright AII and continuum radiance which is absent at low massflows. Electron densities exceed 10 to the 17th power per cu cm, indicating a conductivity of 10,000 mhos per m at the cavity exit for an electron temperature of only a few eV.
The effect on pilot performance of replacing a single electromechanical display with similar cathode-ray-tube displays was studied. The effects of dimensionality, color, and shading were evaluated with respect to the pilot's ability to interpret and respond to displayed information.
A source for the continuous production of neutral metastable atoms is described. A hollow cathode discharge tube was used to produce densities of 3.5 times 10 to the 13th per cu cm and column densities of 1.6 times 10 to the 15th per sq cm in the 4s(2)2D metastable term of neutral copper. The accuracy of these density determinations (+ or - 30 to + or - 66%) is limited by the oscillator strengths required for the analysis. The usefulness of the source was demonstrated by measurements of relative oscillator strengths of some Cu I lines in the 2200 A wavelength region. These data are compared with those obtained by other methods.
It is possible to obtain uniform stable long-pulse excitation (in excess of 100 microsec) in gas mixtures involving highly electronegative constituents (SF6, CCl4, NF3, and I2). Such a system was used to investigate the atomic fluorine laser. In the hollow cathode, lasing on fluorine transitions in the doublet system lasted for up to 80 microsec with no signs of the self-termination as reported previously in positive-column devices. The excitation process of the laser appears to depend heavily upon the fluorine donor utilized. For instance, a single-step process is involved when NF3 is used whereas a two-step process is evident for SF6. The details are discussed.
Improved hollow cathode for neutral-beam injector ion sources rapidly started by dielectric breakdown of ignitor plug located at one end of open ended tube. Used in low-current ion implantation, milling, sputtering, and bombardment for surface treatment.
Data are presented on the stability of calibration of some hot-cathode ion gauges: a conventional triode used in the range of 0.0002-0.2 Pa, and Bayard-Alpert-type gauges used in the range of 0.0002-0.02 Pa. Numerical magnitudes are given of the systematic corrections that must be applied to the gauge indication in order to achieve the highest accuracy of pressure indication. The relative sensitivities of these gauges to Ar, N2, Ne, and He are also given.
The objectives are to optimize the transport rates in electronically conductive polypyrrole films by controlling the morphology of the film and to assess the utility of these films as cathodes in a lithium/polypyrrole secondary battery. During this research period, a better understanding was gained of the fundamental electrochemical switching processes within the polypyrrole film. Three publications were submitted based on the work completed.
Improved reservoir cathode serves as intense source of electrons required for high-frequency and often high-output-power, linear-beam tubes, for which long operating lifetime important consideration. High emission-current densities obtained through use of emitting surface of relatively-low effective work function and narrow work-function distribution, consisting of coat of W/Os deposited by sputtering. Lower operating temperatures and enhanced electron emission consequently possible.
The performance is reported of a field emission array characterized for the purpose of replacing the filament in a trapped ion frequency standard. This dark electron emitter eliminates the need for the interference filter currently used in the trapped ion standard. While reducing the filament's unwanted light, this filter causes a significant reduction in the signal. The magnetic field associated with the filament is also eliminated, thus potentially improving the present stability of the trapped ion standard. The operation of the filament in the present system is described, as well as the associated concerns. The cathode considered for the filament's replacement is then described along with the experimental system. Experimental results, observations, and conclusions are presented.
The objectives of this project are to optimize the transport rates in electronically conductive polypyrrole films by controlling the morphology of the film and to assess the utility of these films as cathodes in a lithium/polypyrrole secondary battery. During this research period, progress has been made in improving the charge transport rate of the supermolecular-engineered polypyrrole electrode by eliminating the polypyrrole baselayer that hampered earlier work. Also, the fibril density of the polypyrrole electrode was increased, providing more electroactive sites per unit area.
It is desirable to employ a corrosion screening test for catalyst or support candidates for the fuel cell cathode before entering upon optimization of the candidate or of the catalytic electrode. To this end, corrosion test electrodes, intended for complete immersion and maximum wetting, have been made with 30 to 40 vol. pct Teflon; with perovskites this is about 10 to 15 pct. The candidates were synthesized by methods intended for single-phase product without special emphasis on high surface area, although the substances tested were no coarser than 2 m squared/g. A typical loading was 25 mg/cm sq of the pure substance, usually on gold screen, a few mm squared of which were left bare for contacting. Contact to the gold lead wire was made by welding with a micro-torch or a spot-welder. Corrosion testing consisted of obtaining current-voltage data under flowing inert gas in the potential region for reduction of O2. The electrode was immersed in 30 pct KOH. Observations were made at 20 C and 80 C, and the results compared with data from gold standards. Results with some perovskites, pyrochlores, spinels, and interstitial compounds will be discussed.
NbSe3 exhibits superior characteristics such as high capacity, high volumetric and gravimetric energy densities, and high discharge rate capability, as compared to other intercalating cathodes. This paper reports the preparation, characterization, and performance of NbSe3. Several electrochemical techniques, such as cyclic voltammetry, constant-current/constant-potential discharges, dc potentiodynamic scans, ac impedance, and ac voltammetry, have been used to give insight to the mechanisms of intercalation of three lithiums with NbSe3 and also into the rate determining process in the reduction of NbSe3.
The X-ray diffraction patterns of 100 percent discharged Schawinigan black cathodes from Li/SOCl2-LiAlCl4 cells were obtained using a high resolution Guinier camera. The previous assignments of the diffraction lines to Li2O2 and rhombohedral sulfur are all found to be incorrect; all sharp Bragg diffraction lines not assignable to anhydrous LiCl can be assigned to LiCl.H2O.