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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 91 records · Page 5
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NASA NTRS2002

Effects of Lateral Plasma Density and Temperature Diffusion on VCSEL Performance

The hydrodynamic model is further verified by applying to a gain-guided single mode VCSEL. DC effects of D(sub NN): (1) increase threshold current J(sub th) and decrease slope efficiency; (2) within the studied range (50% pumping within threshold and realistic diffusion coefficient for a single mode), the L-I relation scales with the relative Injection current (J/J(sub th) - 1). AC effects of D(sub NN): (1) decrease spectral bandwidth and responsivity of direct-current modulation; (2) within the studied range, the frequency response follows the same formal dependence as predicted without diffusion and under a linear gain model, while the resonant frequency position similarly scales with the relative injection current; (3) therefore, it is concluded that the AC effects of D(sub NN) is purely of static nature and reflected via its influence on ot and J(sub th). Within this study, the nonlinear effects of D(sub NN) are mostly reproducible with an equivalent constant diffusion coefficient.

Li, Jian-Zhong↗
NASA NTRS1979

Radial diffusion of Io-injected plasma

The paper reexamines the problem of particle injection by Io and subsequent radial diffusion by flux tube interchange using a proper phase space density formulation. The mathematical formalism is developed, and the theoretical results are compared with the observations, taking into account the pitch angle and energy coverage of the detector on Pioneer 10. Two objectives are pursued: (1) to test the hypothesis of Siscoe and Chen (1977) that Io is the source for all of the plasma observed by Frank et al. (1976) inside 10 R(J); and (2) to describe a simple but flexible method intended to analyze the observations of any other plasma instrument flown through the inner Jovian magnetosphere, e.g., those on Voyager 1 and 2 and Galileo.

Goertz, C. K.↗
NASA NTRS1980

Mass-loading and diffusion-loss rates of the Io plasma torus

Limits to the mass-loading and diffusion-loss rates of ions in the Io plasma torus have been calculated on the assumption that observed optical emissions are controlled by electron-ion collisions. Calculations of the yield of emission from the vicinity of Io limit the mass-loading rate to the order of 10 to the 27th per s for S II or O II, on the grounds that electron-excited emissions associated with the location of Io have not been observed in the optical spectrum. This mass-loading limit is dependent on the assumptions that Io is the source of torus particles and that most of the neutral atoms are converted to ions within 1 R(J) of Io. According to the calculations presented below, the observed partitioning of sulfur ion species in the hot torus at the time of Voyager 1 encounter indicates that the diffusion-loss time of the ions is of the order of 1/D = 100 days. The two results limiting the mass-loading and diffusion-loss rates are compatible and suggest that the energy required to maintain the observed radiated power cannot be supplied by acceleration of ions formed at Io in Jupiter's rotating magnetic field.

Shemansky, D. E.↗
NASA NTRS1978

Possible origins of time variability in Jupiter's outer magnetosphere. III - Variations in the heavy ion plasma

The implications of a heavy ion plasma in the Jovian magnetosphere are discussed. The plasma electron density varies on time scales comparable with that of radial diffusion. This plasma can enhance a super-Alfvenic planetary wind by increasing the radial mass flux. A mechanism by which the heavy ion plasma can regenerate itself via self-sputtering from the surface of Io followed by ionization first by solar ultra-violet and later by electron impact is proposed. It is suggested that this long term variability can modulate the faster variations of the plasma-magnetosphere configuration of Jupiter.

Eviatar, A.↗
NASA NTRS1986

Jovian magnetospheric processes

Jupiter's rotational energy (6 x 10 to the 34th J) powers a large number of processes such as auroral UV emission, radio waves, and charged particle energization. How the rotational energy may be dissipated by injection of plasma, magnetic pumping and field aligned electric fields is described. In addition, energization by radial diffusion and plasma wave absorption is described. The generation of Alfven waves by the moon Io, and their relation to the emission of the Jovian decametric (DAM) radio waves are also described.

Goertz, C. K.↗
NASA NTRS1981

Energetic oxygen and sulfur in the Jovian magnetosphere

Measurements made in the Jovian magnetosphere by the cosmic ray subsystem on Voyager 1 and 2 are reported. Energy spectra of oxygen ions in the energy range 1-20 MeV/nuc between 5 and 20 Jovian radii are presented, and phase space densities are calculated. A steep positive radial gradient in the phase space density of the energetic oxygen ions is observed, indicating an inward diffusive flow. The upper limit on the rate at which oxygen ions with greater than 400 MeV/nuc-G diffuse across 10 Jovian radii is calculated to be 5 x 10 to the 21st ions per second, indicating that about 10 to the -7th of the ions from Io are accelerated to over 400 MeV/nuc-G and diffuse to 10 Jovian radii. Observations also suggest that oxygen and sulfur ions in the Io plasma torus diffuse radially outward, are nonadiabatically accelerated in a region outside 17 Jovian radii, and diffuse inward and outward from the accelerated region.

Gehrels, N.↗
NASA NTRS1983

A perpendicular ion beam instability - Solutions to the linear dispersion relation

A 200-eV Xe(+) ion beam directed perpendicular to the terrestrial magnetic field in the F region ionosphere produced very narrow band electrostatic emissions just above multiples of the hydrogen cyclotron frequency. Although the plasma conditions associated with the ion beam were undoubtedly very complex, a simple ion beam in a background ionosphere is considered first. The dispersion relation for flute mode waves and an unmagnetized perpendicular ion beam is solved for a diffuse H(+) plasma and then for a combination of dense O(+) and diffuse H(+). These solutions account for most of the wave properties, including the observation of narrow spectral peaks separated by the hydrogen cyclotron frequency and the observation of no spectral peaks below 2000 Hz. We cannot dismiss field-aligned currents associated with the Xe(+) beam as an alternate source of free energy for the narrow band emissions. However, our intention here is to examine closely the Xe(+) beam as a source for directly exciting the plasma waves.

Kintner, P. M.↗
NASA NTRS1984

The plasma wave environment of an auroral arc - Electrostatic ion cyclotron waves in the diffuse aurora

Electric field plasma wave observations were made with a sounding rocket payload in and near a quiet auroral arc. This payload was launched on March 9, 1978 from Poker Flat, Alaska. The payload trajectory was close to the magnetic meridian and passed over a 40 kR auroral arc. The present investigation is concerned with ac electric field observations in the ELF and lower VLF covering a frequency range from 2.5 Hz to 8 kHz. Attention is given to aspects of instrumentation, the general situation, a data analysis, and the obtained results. Waves were observed at low altitude in a region of downward parallel current and diffuse aurora. These waves had properties consistent with those expected for hydrogen and oxygen electrostatic ion cyclotron (EIC) waves.

Bering, E. A.↗
NASA NTRS1992

Static and dynamic loop models and their observational signatures

The magnetically closed regions of the outer solar atmosphere can be studied in terms of one dimensional hydrodynamic loops models. These regions include the bright plasma loops that are readily visible in EUV and X-ray images as well as the fainter, more diffuse-appearing plasma that surrounds them. The basic theoretical properties of static, steady state, and time dependent loop models are discussed, and these properties are related to observations of emission measure distributions and Doppler shifts. Both existing observations and future observations from the Solar and Heliospheric Observatory (SOHO) are considered. In particular, the dependence of the models on the form of the energy input (coronal heating) is emphasized.

Klimchuk, James A.↗
NASA NTRS1973

Plasma sheet at lunar distance - Characteristics and interactions with the lunar surface

The plasma sheet at lunar distance is investigated with the use of data from the charged particle lunar environment experiment (CPLEE), complemented with data from the Explorer 35/ARC magnetometer. It is shown that the presence of the lunar surface does not appreciably affect measurements of the plasma sheet characteristics by the lunar-based CPLEE instrument. In particular, the lunar surface generally does not shadow plasma sheet particles. This may be due to rapid random passage (greater than 40 km/sec) of magnetotail field lines with respect to the lunar surface or to diffusion of plasma sheet electrons into the flux tubes in contact with the lunar surface. The plasma sheet is generally observed as a rapid increase in observed particle fluxes and a simultaneous decrease in field strength. A statistical analysis of the CPLEE data shows that the plasma sheet in the midnight sector has a thickness of 5 R sub E plus or minus 2 R sub E. Geomagnetic activity reduces the probability of encounters between the moon and the plasma sheet.

Rich, F. J.↗
NASA NTRS1979

Diffuse Jovian aurora influenced by plasma injection from Io

The paper demonstrates that the broad band of whistler-mode waves observed within the high density torus surrounding Io is consistent with electron cyclotron generation. Cyclotron resonant instability of Jovian energetic electrons is enhanced due to the lower resonant electron energy within the equatorial high density plasma torus surrounding the orbit of Io. The higher energy resonant electron scattering and the corresponding energetic electron lifetimes indicate that an efficient local acceleration process is required to replenish the precipitating relativistic electrons. Calculated energy deposition into the Jovian atmosphere should provide a dominant source of middle atmospheric ionization and excite a continuous band of diffuse auroral emission. It is suggested that the diffuse Jovian aurora should be influenced by the variable volcanic activity on Io which is thought to be an important source of plasma, since the cyclotron scattering process is strongly influenced by the ambient equatorial thermal plasma density.

Thorne, R. M.↗
NASA NTRS1980

Ionospheres of the terrestrial planets

The theory and observations relating to the ionospheres of the terrestrial planets Venus, the earth, and Mars are reviewed. Emphasis is placed on comparing the basic differences and similarities between the planetary ionospheres. The review covers the plasma and electric-magnetic field environments that surround the planets, the theory leading to the creation and transport of ionization in the ionospheres, the relevant observations, and the most recent model calculations. The theory section includes a discussion of ambipolar diffusion in a partially ionized plasma, diffusion in a fully ionized plasma, supersonic plasma flow, photochemistry, and heating and cooling processes. The sections on observations and model calculations cover the neutral atmosphere composition, the ion composition, the electron density, and the electron, ion, and neutral temperatures.

Schunk, R. W.↗
NASA NTRS1999

Shock Wave Dynamics in Weakly Ionized Plasmas

An investigation of the dynamics of shock waves in weakly ionized argon plasmas has been performed using a pressure ruptured shock tube. The velocity of the shock is observed to increase when the shock traverses the plasma. The observed increases cannot be accounted for by thermal effects alone. Possible mechanisms that could explain the anomalous behavior include a vibrational/translational relaxation in the nonequilibrium plasma, electron diffusion across the shock front resulting from high electron mobility, and the propagation of ion-acoustic waves generated at the shock front. Using a turbulence model based on reduced kinetic theory, analysis of the observed results suggest a role for turbulence in anomalous shock dynamics in weakly ionized media and plasma-induced hypersonic drag reduction.

Johnson, Joseph A., III↗
NASA NTRS2010

Neutral Atom Diffusion in a Partially Ionized Prominence Plasma

The support of solar prominences is normally described in terms of a magnetic force on the prominence plasma that balances the solar gravitational force. Because the prominence plasma is only partially ionized. it is necessary to consider in addition the support of the neutral component of the prominence plasma. This support is accomplished through a frictional interaction between the neutral and ionized components of the plasma, and its efficacy depends strongly on the degree of ionization of the plasma. More specifically, the frictional force is proportional to the relative flow of neutral and ion species, and for a sufficiently weakly ionized plasma, this flow must be relatively large to produce a frictional force that balances gravity. A large relative flow, of course, implies significant draining of neutral particles from the prominence. We evaluate the importance of this draining effect for a hydrogen-helium plasma, and consider the observational evidence for cross-field diffusion of neutral prominence material,

Gilbert, Holly↗