Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “collisionless plasma”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The aerodynamics of bodies in a rarefied ionized gas with applications to spacecraft environmental dynamics

The objectives are to provide a parametric description of the electrostatic interaction of a mesosonic, collisionless plasma with conducting bodies on the order of 1 to 10 Debye lengths in size, and to extend this description to the satellite-ionospheric interaction, where possible. Experimental findings include: the wake of the geometrically complex body appears to be a linear superposition of the wakes of its simple geometric components; and vector ion flux measurements show converging ion streams at the wake axis and direct evidence of ion streams deflected from the wake axis by the positive space charge potential associated with the axial ion peak. The extension to the satellite-ionospheric interaction utilizes qualitative scaling and indicates that similar, but smaller amplitude, wake structures may be expected for small or highly charged bodies. However, for large bodies at small potentials, the structure may be diffused by the thermal ion motion and the dispersion resulting for space charge potentials.

Stone, N. H.↗
NASA NTRS1981

Kinetic response of ionospheric ions to onset of auroral electric fields

By examining the exact analytic solution of a kinetic model of collisional interaction of ionospheric ions with atmospheric neutrals in the Bhatnagar-Gross-Krook approximation, we show that the onset of intense auroral electric fields in the topside ionosphere can produce the following kinetic effects: (1) heat the bulk ionospheric ions to approximately 2 eV, thus driving them up to higher altitudes where they can be subjected to collisionless plasma processes; (2) produce a non-Maxwellian superthermal tail in the distribution function; and (3) cause the ion distribution function to be anisotropic with respect to the magnetic field with the perpendicular average thermal energy exceeding the parallel thermal energy.

Chiu, Y. T.↗
NASA NTRS1981

Kinetic response of ionospheric ions to onset of auroral electric fields

Examination of the exact analytic solution of a kinetic model of collisional interaction of ionospheric fions with atmospheric neutrals in the Bhatnagar-Gross-Krook approximation, shows that the onset of intense auroral electric fields in the topside ionosphere can produce the following kinetic effects: (1) heat the bulk ionospheric ions to approximately 2 eV, thus driving them up to higher altitudes where they can be subjected to collisionless plasma processes; (2) produce a nonMaxwellian superthermal tail in the distribution function; and (3) cause the ion distribution function to be anisotropic with respect to the magnetic field with the perpendicular average thermal energy exceeding the parallel thermal energy.

Chiu, Y. T.↗
NASA NTRS1982

A new theory of sources of Birkeland currents

An approach to collisionless plasma shows the existence of current orthogonal to B along the low latitude boundary layer of the magnetosphere driven by electric field which is orthogonal to both B and the layer. In this case relationship P perpendicular + (sq B/8 pi) - (sq epsilon E perpendicular/8 pi) = constant holds on a line orthogonal to B and the layer, where epsilon is the dielectric constant of the plasma for electric fields orthogonal to B. Across the geomagnetic tail there flows a current in the direction of the dawn-dusk electric field, and in this case a relationship P perpendicular + (sq B/8 pi) + (sq epsilon E perpendicular/8 pi = constant, holds aong a line orthogonal to E and B. Divergence of both these currents is shown to be a source of Birkeland currents. Some of the boundary layer current is continuous with current across the tail. Electric currents of physically similar origin flow in interplanetary space, and when the magnetosphere interrupts them, additional Birkeland currents are driven.

Cole, K. D.↗
NASA NTRS1983

Theory of hydromagnetic waves in the magnetosphere

A survey of theoretical and experimental research on the origin and characteristics of low-frequency hydromagnetic (HM) waves in the magnetosphere is presented, with a focus on advances in theory made in the last ten years. Basic wave theory and a collisionless plasma theory are applied to the magnetosphere as a HM system. Continuous energy sources are considered, such as the Kelvin-Helmholtz instability, the ring-current plasma, and drift instabilities. Other topics discussed include the theory of inhomogeneous HM waves, signal behavior in atmosphere and ionosphere, Alfven waves and ionosphere-magnetosphere coupling, Pi2 signals, damping, pulsating aurora, heavy-ion scattering, and standing waves in high-speed flows (like the wake phenomena caused on Jupiter by the passing of Io, observed by Voyager 1).

Southwood, D. J.↗
NASA NTRS1984

The collisionless macroscopic Kelvin-Helmholtz instabiity. I Transverse electrostatic mode

The electrostatic limit of the Kelvin-Helmholtz instability in a collisionless plasma is investigated for a magnetic field perpendicular to the velocity flow. A two-fluid eigenvalue analysis of the transverse electrostatic Kelvin-Helmholtz instability is performed using the Chew-Goldberger-Low hydromagnetic equations with first-order finite Larmer radius corrections, establishing that the transverse electrostatic mode reduces to the incompressible transverse MHD mode in the limit of zero ion gyroradius. The linear growth rates are determined and a strong stabilization of the instability for (k-perpendicular) (rho sub i) of 0.2 or greater is observed. The nonlinear stage of the instability displays large vortices whose size is many times the initial velocity shear length. At saturation the simulation is dominated by the longest-wavelength mode permitted in the system. The simulation results can be understood in terms of a simple model which assumes that saturation occurs when the angular frequency of the vortex motion reaches the linear growth rate of the instability.

Prichett, P. L.↗
NASA NTRS1984

Nonlinear mode coupling theory of the lower-hybrid-drift instability

A nonlinear mode coupling theory of the lower-hybrid-drift instability is presented. A two-dimensional nonlinear wave equation is derived which describes lower-hybrid drift wave turbulence in the plane transverse to B (k.B = 0), and which is valid for finite beta, collisional and collisionless plasmas. The instability saturates by transferring energy from growing, long wavelength modes to damped, short wavelength modes. Detailed numerical results are presented which compare favorably to both recent computer simulations and experimental observations. Applications of this theory to space plasmas, the earth's magnetotail and the equatorial F region ionosphere, are discussed. Previously announced in STAR as N84-17734

Drake, J. F.↗
NASA NTRS1984

Magnetospheric currents; Chapman Conference, Irvington, VA, April 5-8, 1983, Selected Papers

A description is presented of theory and models, taking into account magnetospheric dynamo processes, magnetospheric topology of fields and currents, a new theory of sources of Birkeland currents, dielectric and permeability effects in collisionless plasmas, field-aligned current sheets as tangential and rotational discontinuities, electrodynamics of convection in the inner magnetosphere, coupling of Birkeland current rings, region one Birkeland currents connecting to sunward convecting flux tubes, and corrected geomagnetic coordinates for epoch 1980. Other topics explored are related to early history, an introduction to magnetospheric currents, surface observations, near-space observations, distant space observations, ionospheric effects, plasma instabilities, and current systems in other magnetospheres. Attention is given to the dynamics of field-aligned current sources at earth and Jupiter, fundamentals of current description, polar cap current systems, electric fields and currents associated with active aurora, and the role of currents in plasma redistribution.

Potemra, T. A.↗
NASA NTRS1984

A new theory of sources of Birkeland currents

An approach to collisionless plasma shows the existence of current orthogonal to B along the low latitude boundary layer of the magnetosphere driven by electric field which is orthogonal to both B and the layer. In this case relationship P perpendicular + (sq B/8 pi) - (sq epsilon E perpendicular/8 pi) = constant holds on a line orthogonal to B and the layer, where epsilon is the dielectric constant of the plasma for electric fields orthogonal to B. Across the geomagnetic tail there flows a current in the direction of the dawn-dusk electric field, and in this case a relationship P perpendicular + (sq B/8 pi) + (sq epsilon E perpendicular/8 pi) = constant, holds along a line orthogonal to E and B. Divergence of both these currents is shown to be a source of Birkeland currents. Some of the boundary layer current is continuous with current across the tail. Electric currents of physically similar origin flow in interplanetary space, and when the magnetosphere interrupts them, additional Birkeland currents are driven.

Cole, K. D.↗
NASA NTRS1985

The second-order theory of electromagnetic hot ion beam instabilities

The present investigation is concerned with the application of a second-order theory for electromagnetic instabilities in a collisionless plasma to two modes which resonate with hot ion beams. The application of the theory is strictly limited to the linear growth phase. However, the application of the theory may be extended to obtain a description of the beam at postsaturation if the wave-beam resonance is sufficiently broad in velocity space. Under the considered limitations, it is shown that, as in the cold beam case, the fluctuating fields do not gain appreciable momentum and that the primary exchange of momentum is between the beam and main component.

Gary, S. P.↗
NASA NTRS1985

Ion reflection, gyration, and dissipation at supercritical shocks

Topics on collisionless plasmas are discussed and include: (1) Ion reflection is the dominant ion dissipation mechanism at nearly perpendicular, supercritical shocks. (2) An increasing fraction of the ions incident on a supercritical shock is reflected as the Mach number increases. The actual fraction reflected can be predicted using the Rankine Hugoniot conservation relations. (3) The effective temperature associated with the dispersion in velocity space associated with ion reflection accounts for a large fraction of the temperature rise observed across supercritical, quasi perpendicular shocks.

Gosling, J. T.↗
NASA NTRS1987

On the noncoplanarity of the magnetic field within a fast collisionless shock

Within the magnetic ramp of fast collisionless plasma shocks observed with spacecraft instruments and simulated numerically, the magnetic field undergoes an excursion out of the plane of coplanarity. This rotation is consistently in the direction such that the electrostatic potential jump across the shock, as measured in the de Hoffman-Teller frame of the reference (HTF), is about 2-6 times smaller than the electrostatic potential jump measured in the normal incidence frame. The preferred direction is consistent with a basic whistler mode transition between the upstream and downstream orientations. The potential jump in the HTF is considerably smaller than the change in bulk flow energy across the shock, confirming the recent suggestion that magnetic forces contribute importantly to the slowing of the plasma in that frame. A further consequence is that suprathermal particles leaking back into the upstream region across the shock do not gain much energy from the cross-shock electric field.

Thomsen, M. F.↗
NASA NTRS1988

Kinetic theory for electrostatic waves due to transverse velocity shears

A kinetic theory in the form of an integral equation is provided to study the electrostatic oscillations in a collisionless plasma immersed in a uniform magnetic field and a nonuniform transverse electric field. In the low temperature limit the dispersion differential equation is recovered for the transverse Kelvin-Helmholtz modes for arbitrary values of K parallel, where K parallel is the component of the wave vector in the direction of the external magnetic field assumed in the z direction. For higher temperatures the ion-cyclotron-like modes described earlier in the literature by Ganguli, Lee and Plamadesso are recovered. In this article, the integral equation is reduced to a second-order differential equation and a study is made of the kinetic Kelvin-Helmholtz and ion-cyclotron-like modes that constitute the two branches of oscillation in a magnetized plasma including a transverse inhomogeneous dc electric field.

Ganguli, G.↗
NASA NTRS1991

On the auroral current-voltage relationship

The auroral relationship between the upward parallel current and the parallel potential drop is predicted using Knight's (1973) collisionless-plasma kinetic theory, and the results are compared with near-simultaneously carried out measurements by DE 1 and DE 2. The agreement between the calculated and observed data is generally good. However, the Knight current, since it does not include upward ionospheric electrons, is not valid in the downward return current region. It was found that suprathermal electron bursts could be observed in the diffuse aurora at the same invariant latitudes, both at high and at low altitudes, suggesting that these bursts are a spatial rather than temporal phenomenon.

Lu, G.↗
NASA NTRS1991

The formation of quasi-parallel shocks

In a collisionless plasma, the coupling between a piston and the plasma must take place through either laminar or turbulent electromagnetic fields. Of the three types of coupling (laminar, Larmor and turbulent), shock formation in the parallel regime is dominated by the latter and in the quasi-parallel regime by a combination of all three, depending on the piston. In the quasi-perpendicular regime, there is usually a good separation between piston and shock. This is not true in the quasi-parallel and parallel regime. Hybrid numerical simulations for hot plasma pistons indicate that when the electrons are hot, a shock forms, but does not cleanly decouple from the piston. For hot ion pistons, no shock forms in the parallel limit: in the quasi-parallel case, a shock forms, but there is severe contamination from hot piston ions. These results suggest that the properties of solar and astrophysical shocks, such as particle acceleration, cannot be readily separated from their driving mechanism.

Cargill, Peter J.↗
NASA NTRS1994

Hybrid simulations of whistler waves generation and current closure by a pulsed tether in the ionosphere

The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, sudden switch-on current source across the magnetic field has been studied using a two dimensional hybrid code. It was found that the predominant plasma response was the excitation of whistler waves and the formation of current closure by induced currents in the plasma. The results show that the current closure path consists of: (a) two antiparallel field-aligned current channels at the end of the imposed current sheet; and (b) a cross-field current region connecting these channels. The formation of the current closure path occured in the whistler timescale much shorter than that of MHD and the closure region expanded continuously in time. The current closure process was accompanied by significant energy loss due to whistler radiation.

Chang, C. L.↗
NASA NTRS1994

A hybrid simulation of contact discontinuity

Contact discontinuities in a collisionless plasma are studied by hybrid simulations, in which ions are treated as particles and electrons are considered as a fluid. It is demonstrated that contact discontinuity with a stable density ramp can exist in cases with a finite electron temperature. An electron pressure gradient is present across the contact discontinuity, leading to the presence of a parallel electric field and hence field-aligned potential increase (Delta Phi (sub parallel)) in the transition region. By reflecting ions at the discontinuity, this parallel electric potential peak reduces the interpenetration between hot and cold ions and maintains a stable density ramp across the contact discontinuity. The ratio of the field-aligned electric potential energy to ion thermal energy, e(Delta) Phi(sub parallel)/kT(sub i), is found to be an increasing function of T(sub e)/T(sub i), where T(sub e) and T(sub i) are respectively the electron and ion temperature.

Wu, B. H.↗
NASA NTRS1995

Anisotropic shock jump conditions: Theory and observations

The MHD Rankine-Hugoniot (RH) relations for shock waves in a collisionless plasma with bi-Maxwellian distribution functions are considered. While by introducing the pressure anisotropy parameter xi in the RH relations, the number of unknowns -- B, V, n, p and xi (a total of 9) -- becomes one more than the total number of the conservation equations, it is possible to use the observed quantities on both sides of the shock to study the anisotropy changes across the shock. A simple relation for the anisotropy change across the shock is derived as a function of the ratio of magnetic fields m(= B'/B), the shock normal angle theta(sub Bn) and the plasma beta and beta' (primes are downstream values). Since m and theta(sub Bn) can be determined accurately in observation, the reliability of the anisotropy change deduced is mostly dependent on the accuracy of the measurements beta and beta'. We have applied the results to six low-beta quasi-perpendicular (Q perpendicular) laminar bow shock crossings with temperature anisotropy measured in the magnetosheath. In the six test cases, it is found that the predicted pressure anisotropies agree well with those observed in the magnetosheath.

Chao, J. K.↗