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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Trapping effects in irradiated and avalanche-injected MOS capacitors

The trapping parameters for holes, and for electrons in the presence of trapped holes, have been measured from a set of wafers with different oxide thickness processed under controlled conditions. The trap cross-sections and densities indicate at least three trap species, including an interfacial species, a dominant bulk species which is determined to tail off from the silicon interface, and a third, lower density bulk species that is distributed throughout the oxide.

Bakowski, M.↗
NASA NTRS1987

Charge exchange avalanche at the cometopause

A sharp transition from a solar wind proton dominated flow to a plasma population primarily consisting of relatively cold cometary heavy ions has been observed at a cometocentric distance of about 160,000 km by the VEGA and GIOTTO missions. This boundary (the cometopause) was thought to be related to charge transfer processes, but its location and thickness are inconsistent with conventionally estimated ion - neutral coupling boundaries. In this paper a two-fluid model is used to investigate the major physical processes at the cometopause. By adopting observed comet Halley parameters the model is able to reproduce the location and the thickness of this charge exchange boundary.

Gombosi, Tamas I.↗
NASA NTRS1988

Microwave and millimeter-wave power generation in silicon carbide avalanche devices

Numerical simulations were performed to investigate the typical power-generating capabilities of SiC IMPATT diodes. Using available material parameters, SiC double-drift IMPATT diodes were simulated at 10, 35, 60, and 94 GHz, and the operating characteristics of these devices were compared to those of Si and GaAs devices. Compared to the Si and GaAs IMPATT performances in the pulsed mode, the SiC IMPATT performance was found to be far superior. The performance of SiC devices in the CW mode was also superior to that of GaAs devices, especially at lower frequencies. At a high frequency (94 GHz), the performance of the SiC device was found to be comparable to that of Si devices.

Mehdi, I.↗
NASA NTRS1990

Soft switch-avalanche IGBT convertor

A full bridge dc-dc converter using a zero voltage and zero current switching technique is described. This circuit utilizes the characteristics of the IGBT to achieve power and frequency combinations that are much higher than those previously reported for this device. Experimental results are included for a 1.5 kW, 100 kHz converter with 94 percent efficiency.

Chen, K.↗
NASA NTRS2006

Characterization and Modeling of Indium Gallium Antimonide Avalanche Photodiode and of Indium Gallium Arsenide Two-band Detector

A model of the optical properties of Al(x)Ga(1-x)As(y)Sb(1-y) and In(x)Ga(1-x)As(y)Sb(1-y) is presented, including the refractive, extinction, absorption and reflection coefficients in terms of the optical dielectric function of the materials. Energy levels and model parameters for each binary compound are interpolated to obtain the needed ternaries and quaternaries for various compositions. Bowing parameters are considered in the interpolation scheme to take into account the deviation of the calculated ternary and quaternary values from experimental data due to lattice disorders. The inclusion of temperature effects is currently being considered.

Source record↗
NASA NTRS2012

Seasonally Active Slipface Avalanches in the North Polar Sand Sea of Mars: Evidence for a Wind-Related Origin

Meter-scale MRO/HiRISE camera images of dune slipfaces in the north polar sand sea of Mars reveal the presence of deep alcoves above depositional fans. These features are apparently active under current climatic conditions, because they form between observations taken in subsequent Mars years. Recently, other workers have hypothesized that the alcoves form due to destabilization and mass-wasting during sublimation of CO2 frost in the spring. While there is evidence for springtime modification of these features, our analysis of early springtime images reveals that over 80% of the new alcoves are visible underneath the CO2 frost. Thus, we present an alternative hypothesis that formation of new alcoves and fans occurs prior to CO2 deposition. We propose that fans and alcoves form primarily by aeolian processes in the mid- to late summer, through a sequence of aeolian deposition on the slipface, over-steepening, failure, and dry granular flow. An aeolian origin is supported by the orientations of the alcoves, which are consistent with recent wind directions. Furthermore, morphologically similar but much smaller alcoves form on terrestrial dune slipfaces, and the size differences between the terrestrial and Martian features may reflect cohesion in the near-subsurface of the Martian features. The size and preservation of the largest alcoves on the Martian slipfaces also support the presence of an indurated surface layer; thus, new alcoves might be sites of early spring CO2 sublimation and secondary mass-wasting because they act as a window to looser, less indurated materials that warm up more quickly in the spring.

Horgan, Briony H. N.↗
NASA NTRS2015

Is the Electron Avalanche Process in a Martian Dust Devil Self-Quenching?

Viking era laboratory experiments show that mixing tribocharged grains in a low pressure CO2 gas can form a discharge that glows, indicating the presence of an excited electron population that persists over many seconds. Based on these early experiments, it has been predicted that martian dust devils and storms may also contain a plasma and new plasma chemical species as a result of dust grain tribo-charging. However, recent results from modeling suggest a contrasting result: that a sustained electron discharge may not be easily established since the increase in gas conductivity would act to short-out the local E-fields and quickly dissipate the charged grains driving the process. In essence, the system was thought to be self-quenching (i.e., turn itself off). In this work, we attempt to reconcile the difference between observation and model via new laboratory measurements. We conclude that in a Mars-like low pressure CO2 atmosphere and expected E-fields, the electron current remains (for the most part) below the expected driving tribo-electric dust currents (approx. 10 microA/m(exp. 2)), thereby making quenching unlikely.

Electron↗