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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Thermionic Fuel Element with Cermet Fuel

A method of calculating and the computational results obtained for the time variation of the radial deformation of the fuel-element cladding of a single-element EGC based on cermet with a polycrystalline molybdenum matrix in which uranium dioxide particles are distributed are presented. It is shown that the maximum admissible deformation of cladding comprised of 1-mm thick, hardened, single-crystalline, tungsten-tantalum alloy with a 10 mm in diameter central channel in the kernel is reached in 10 years.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2013

Joule heat generation in thermionic cathodes of high-pressure arc discharges

The nonlinear surface heating model of plasma-cathode interaction in high-pressure arcs is extended to take into account the Joule effect inside the cathode body. Calculation results are given for different modes of current transfer to tungsten cathodes of different configurations in argon plasmas of atmospheric or higher pressures. Special attention is paid to analysis of energy balances of the cathode and the near-cathode plasma layer. In all the cases, the variation of potential inside the cathode is much smaller than the near-cathode voltage drop. However, this variation can be comparable to the volt equivalent of the energy flux from the plasma to the cathode and then the Joule effect is essential. Such is the case of the diffuse and mixed modes on rod cathodes at high currents, where the Joule heating causes a dramatic change of thermal and electrical regimes of the cathode. The Joule heating has virtually no effect over characteristics of spots on rod and infinite planar cathodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Thermionic power-law decay of excited aluminum-cluster anions and its dependence on storage-device temperature

The decay of excited aluminum-cluster anions (Al{sub n}{sup -}, n=4 and 5) has been investigated in a cryogenic linear ion-beam trap. A power-law is found to accurately reproduce the time dependence of the observed decay rates at early storage times, although the exponents are significantly larger than the typically observed 1/t decay. It is shown that the power-law exponent is, at most, weakly dependent on the cluster electron affinity and heat capacity. A previous power-law exponent model for small clusters is also shown to be in disagreement with both investigated species. The attribution of a drop in the decay rate at later times to radiative cooling as observed in larger molecules also does not appear justified in our case. A strong dependence of the power-law exponent on the ambient temperature was observed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Correlation between microstructure and thermionic electron emission from Os-Ru thin films on dispenser cathodes

Osmium-ruthenium films with different microstructures were deposited onto dispenser cathodes and subjected to 1000 h of close-spaced diode testing. Tailored microstructures were achieved by applying substrate biasing during deposition, and these were evaluated with scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy before and after close-spaced diode testing. Knee temperatures determined from the close-spaced diode test data were used to evaluate cathode performance. Cathodes with a large (10-11) Os-Ru film texture possessed comparatively low knee temperatures. Furthermore, a low knee temperature correlated with a low effective work function as calculated from the close-spaced diode data. It is proposed that the formation of strong (10-11) texture is responsible for the superior performance of the cathode with a multilayered Os-Ru coating.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Thermionic field emission of electrons from the paraboloidal metal micropoint

The problem of determining the emission current as a function of voltage, radius of the micropoint curvature, and the distance between the micropoint and a conducting plane is considered on the basis of the theoretical method developed for determining the electric field in the vicinity of a paraboloidal micropoint near a plane metal surface. The universal current–voltage characteristics for a copper micropoint, which are considered for various distances between the micropoint and the plane, can be used for obtaining quantitative estimates of currents in various physics problems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Single electron transistor: Energy-level broadening effect and thermionic contribution

In this paper, a theoretical study of single electron transistor (SET) based on silicon quantum dot (Si–QD) has been studied. We have used a novel approach based on the orthodox theory. We studied the energy–level broadening effect on the performance of the SET, where the tunnel resistance depends on the discrete energy. We have investigated the I–V curves, taking into account the effects of the energy-level broadening, temperature and bias voltage. The presence of Coulomb blockade phenomena and its role to obtain the negative differential resistance (NDR) have been also outlined.

36 MATERIALS SCIENCE↗