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Results for “Plasma stability”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Passivation of pigment particles for thermal control coatings

Five powders were received for plasma calcining during this report period. The particle size using a fluid energy mill, and obtained pigments that could be plasma calcined. Optimum results are obtained in the plasma calcining of zinc orthotitanate when finely dispersed particles are subjected to a calculated plasma temperature of 1670 C. Increasing the plasma calcining time by using multiple passes through the plasma stabilized the pigment to vacuum UV irradiation was evidenced by the resulting ESR spectra but slightly decreased the whiteness of the pigment. The observed darkening is apparently associated with the formation of Ti(+3) color centers.

Farley, E. P.↗
NASA NTRS1973

Whistler modulational instability.

Derivation of the modulational instability characteristics of whistlers in cold and hot plasmas. The cold-plasma analysis considers both ion motion and relativistic effects; the unstable band, with a growth rate proportional to (B/B sub zero)squared, is contiguous to Omega sub e/4 and, depending on the plasma density, lies above or below that frequency (Omega sub e is the electron cyclotron frequency of the static magnetic field; B and B sub zero are the whistler and static magnetic fields). In hot plasmas, stability occurs between Omega sub e/4 and Omega prime (less than Omega sub e), with Omega prime depending mainly on the mean energy and anisotropy of the energetic electron population; the complementary unstable band has a growth rate proportional to (B/B sub zero) to the 1/2 power. The relevance of the instability to whistlers in the magnetosphere is discussed.

Brinca, A. L.↗
NASA NTRS1961

Concerning Certain Collisionless Plasma-Shock Wave Models

A shock-wave model proposed by both Kahn and Parker for the collision of two interstellar gas clouds or of the solar wind with the ionized gas around the earth is re-evaluated in the light of recent developments in plasma stability theory. It is shown that the instability which was supposed to arrest the counter-streaming of the ions and to transfer much of their kinetic energy to the electrons does not occur in many important examples. Specifically, it is absent if the initial ion thermal energy exceeds 4.2 x 10 (sup -4) times their translational energy. While other plausible shock structures are known which yield supra-thermal electrons, they depend on magnetic fields, leaving no satisfactory theory in the limit of zero magnetic field.

Noerdlinger, Peter D.↗
NASA NTRS1992

Electron-ion hybrid instabilities driven by velocity shear in a magnetized plasma

The stability of a magnetized plasma is investigated in which a sheared electron flow channel is present. The flow's peak velocity and shear scale length are denoted by V and L, respectively. If the velocity channel is perpendicular to the confining magnetic field and L is less than the ion Larmor radius, an electrostatic instability develops whose frequency is on the order of the lower hybrid frequency. It is concluded that velocity shear is the only source of free energy. Further, it is shown that density gradients do not stabilize this mode. It follows that the mode presented in this work can not be identified with the well-known modified two-stream instability. If the velocity channel is parallel to the confining magnetic field and the plasma is weakly magnetized, an instability driven by velocity shear is shown to exist.

Romero, H.↗
NASA NTRS1984

The effect of line-tying on the radiative MHD stability of coronal plasmas with radial pressure profile

The role of photospheric line-tying, i.e., solar coronal loop structures, was investigated in terms of the effect on radiative modes and the influence that different radial pressure profiles exert on the effects of line-tying on radiative MHD stability. Energy is assumed dissipated by heat conduction and radiation and zero- and first-order solutions are obtained for the radiative time scales. Line-tying is a magnetic tension in the zero-order MHD mode and produces stability. Heat conduction occurs along bent field lines in first-order MHD modes when plasmas cross the field lines. Irradiated cool-core loops can experience MHD instabilities in the cylinder center, while line-tying can stabilize the plasma in the surrounding hot medium. Line-tying also adds stability to magnetosonic and condensation modes.

An, C.-H.↗
NASA NTRS1986

The stability of the cometary plasma tail and rays

The stability of both the main cometary plasma tail and the tail rays is considered, taking into account the coupling between the plasma and the neutrals that flow out radially from the nucleus. It is shown that this coupling has a negligible effect on wave damping. Rather, it was found that the neutral wind tends to destabilize the flanks of the main tail. On the other hand, the cometary rays are subject to both stabilizing and destabilizing effects because of the ion-neutrals drag. As a result, helical perturbations should become azimuthally asymmetric. The study predicts that the folding rays may become wavy while approaching the tail axis, whereas they should remain straight far away from the tail axis.

Ershkovich, A. I.↗
NASA NTRS1983

'Stabilization' of the lower-hybrid-drift instability in finite-beta plasmas

The stability properties of the lower-hybrid-drift instability are reexamined for finite-beta plasmas. In contrast to previous results, it is found that finite-beta does not stabilize the instability in the sense that the growth rate becomes negative. Rather, as beta increases, the fastest growing mode shifts to longer wavelengths and makes a transition to an ion-cyclotron mode when the growth rate falls below the ion-cyclotron frequency.

Drake, J. F.↗
NASA NTRS1980

On self-consistent waves and their stability in warm plasmas. II - Instability of circularly polarized waves both in the presence and the absence of an ambient magnetic field

The stability of a self-consistent, large-amplitude, circularly polarized wave in a warm plasma is investigated. For perturbations to the system propagating normal to the plane of circular polarization, a dispersion relation is derived employing an expansion in the nonlinear wave amplitude and the momentum of the plasma particles in the plane of polarization. Instability results both in the absence and presence of a large-scale magnetic field with a growth rate of the order of the nonlinear wave amplitude.

Lee, M. A.↗
NASA NTRS1984

Comments on the MHD stability of coronal plasmas with line-tying

Reasonable boundary conditions and test functions for photospheric line-tying are discussed, and their effects on the ideal MHD stability of coronal loops are considered. It is concluded that the plasma at the footpoints of a loop may safely be assumed to be stationary. When a simple perturbed test function is used for the energy principle, the function should be helical in form. Constraints on the test function should be discarded because they overestimate stability.

An, C.-H.↗
NASA NTRS2001

Interfacial Stability of Converging Plasma Jets for Magnetized Target Fusion

The merging of a spherical distribution of plasma jets to dynamically form a gaseous liner has been proposed for use in magnetized target fusion propulsion. In this paper, a study is made of the interfacial stability of the interaction of these jets. Specifically, the Orr-Sommerfeld equation is integrated to obtain the growth rate of a perturbation to the primary flow at the interface between the colliding jets. The analysis lead to an estimate on the tolerances on the relative flow velocities of the merging plasma jets to form a stable, imploding liner. The results show that during the merging of the jets to form a liner and before contact with the target plasma the growth of the perturbed flow at the jet interface is not likely to destabilize the liner. These data suggest that, as far as the stability of the interface between the merging jets is concerned, the formation of liner can withstand velocity variation up to 50% between the neighboring jets over the density and temperature ranges investigated.

Cassibry, J. T.↗
NASA NTRS1989

Ballooning stability of axisymmetric plasmas with sheared equilibrium flows

A WKB theory is formulated for large-n ballooning modes in axisymmetric, toroidal plasmas with sheared equilibrium flows. The validity of the standard ballooning respresentation is severely restricted in the presence of sheared toroidal flow, despite the fact that to leading order in (1/n), where n is the azimuthal number, the eigenmode equation contains only derivatives along a field line. Necessary and sufficient conditions for stability are obtained in a high-beta ordering for rigid toroidal rotation as well as field-aligned flows.

Bhattacharjee, A.↗
NASA NTRS1979

On self-consistent waves and their stability in warm plasma. I - Construction of the self-consistent waves

Clemmow's (1974) work is extended to include the case of large-amplitude self-consistent waves in warm plasmas both with and without a constant embedded magnetic field. Attention is given to determining the structure and basic properties of large-amplitude self-consistent waves in a warm plasma in the presence of a constant embedded magnetic field. It is shown that the class of large-amplitude self-consistent waves found by Clemmow for a cold plasma can be extended to allow for a thermal spread in the particles' motions. Some of the interesting variations and dependences of such waves with a constant embedded magnetic field are emphasized.

Lee, M. A.↗