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Results for “Alfvenic instabilities”

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Finite beta drift Alfven instability

We propose a means by which the theory of drift instabilities can be extended to plasmas of arbitrary beta. We then concentrate on the drift Alfven instability driven by an electron temperature gradient, proposed by Coroniti and Kennel (1970) to be a source of Pi 1 micropulsations on auroral lines of force. Even at relatively low beta the full finite beta theory differs considerably from previous low beta theories and produces better agreement with observation.

Chance, M. S.↗
NASA NTRS1993

Modulational and decay instabilities of Alfven waves - Effects of streaming He(2+)

The parametric instability of a circularly polarized Alfven wave propagating along the background magnetic field are considered, with emphasis on the effects of a second ion species, He(2+), which drifts relative to the protons. Even though its abundance is small, the He(2+) modifies the dispersion relation of the 'pump' Alfven wave and introduces a new sound wave (alpha sound) in addition to the usual sound wave carried primarily by the electrons and protons. Instabilities which are close to the He(2+) gyroresonance are found. This may provide a means of directly transferring Alfven wave energy to the alpha particles, if the alphas are able to resonantly extract energy from the unstable waves without quenching the instability altogether. Instabilities which are close to the alpha particle sound speed are also found.

Hollweg, Joseph V.↗
NASA NTRS1992

Parametric Instabilities Of Alfven Waves

Report presents theoretical study of parametric instabilities of finite-amplitude, circularly-polarized Alfven waves in plasma having pressure anisotropy. Waves studied are observed in solar wind and conjectured to exist in interstellar and other cosmic plasmas.

Hamabata, Hiromitsu↗
DOE OSTI2024

Collaborative Research: Parametric Instabilities of Alfven Waves in Low‐beta Plasmas

Alfven waves are of fundamental importance in magnetized plasmas. This project aims to advance our understanding of the basic physics of the parametric instabilities of Alfven waves using advanced computer simulations. The results will have implications for important processes in the heliosphere involving Alfven waves, such as coronal heating and solar wind heating.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Tearing Instability in Alfven and Kinetic-Alfven Turbulence

Recently, it has been realized that magnetic plasma turbulence and magnetic field reconnection are inherently related phenomena. Turbulent fluctuations generate regions of sheared magnetic field that become unstable to the tearing instability and reconnection, thus modifying turbulence at the corresponding scales. In this contribution, we give a brief review of some recent results on tearing-mediated magnetic turbulence.We illustrate the main ideas of this rapidly developing field of study by concentrating on two important examples—magnetohydrodynamic Alfven turbulence and small-scale kinetic-Alfven turbulence. Due to various potential applications of these phenomena in space physics and astrophysics, we specifically try not to overload the text by heavy analytical derivations but rather present a qualitative discussion accessible to a non-expert in the theories of turbulence and reconnection.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1988

Filamentation instability of large-amplitude Alfven waves

An instability that leads to the filamentation of large-amplitude Alfven waves and gives rise to purely growing density and magnetic field fluctuations is studied. The dispersion relation of the instability is derived, from which the threshold conditions and the growth rates of the instability are analyzed quantitatively for applications to the solar wind plasma. Their dependence on the filamentation spectrum, the plasma beta, and the pump frequency and intensity was examined for both right-hand and left-hand circularly polarized Alfven waves. The excitation of filamentation instability for certain cases of interest is discussed and compared with that of the parametric decay and modulation instability. The relevance of the proposed instability to some observations is discussed.

Kuo, S. P.↗
NASA NTRS1991

Kelvin-Helmholtz instability in an Alfven resonant layer of a solar coronal loop

A Kelvin-Helmholtz instability has been identified numerically on an azimuthally symmetric Alfven resonant layer in an axially bounded, straight cylindrical coronal loop. The set of equations is solved numerically as an initial value problem. The linear growth rate of this instability is shown to be approximately proportional to the Alfven driving amplitude and inversely proportional to the width of the Alfven resonant layer. It is also shown that the linear growth rate increases linearly with m - 1 up to a certain m, reaches its maximum value for the mode whose half wavelength is comparable to the Alfven resonant layer width, and decreases at higher azimuthal mode number.

Uchimoto, E.↗
DOE OSTI2024

FAR3d

The FAR3d model calculates the linear and nonlinear stability properties of energetic particle driven Alfven instabilities for both tokamak and stellarator plasma confinement devices using gyro-landau closure methods. This is an important fundamental physics problem for existing fusion energy experiments and for future fusion reactors.

Varela, Jacobo↗
NASA NTRS1986

Parametric instabilities of the circularly polarized Alfven waves including dispersion

A class of parametric instabilities of large-amplitude, circularly polarized Alfven waves is considered in which finite frequency (dispersive) effects are included. The dispersion equation governing the instabilities is a sixth-order polynomial which is solved numerically. As a function of K identically equal to k/k-sub-0 (where k-sub-0 and k are the wave number of the 'pump' wave and unstable sound wave, respectively), there are three regionals of instability: a modulation instability at K less than 1, a decay instability at K greater than 1, and a relatively weak and narrow instability at K close to squared divided by v-sub-A squared (where c-sub-s and v-sub-A are the sound and Alfven speeds respectively), the modulational instability occurs when beta is less than 1 (more than 1) for left-hand (right-hand) pump waves, in agreement with the previous results of Sakai and Sonnerup (1983). The growth rate of the decay instability of left-hand waves is greater than the modulational instability at all values of beta. Applications to large-amplitude wave observed in the solar wind, in computer simulations, and in the vicinity of planetary and interplanetary collisionless shocks are discussed.

Wong, H. K.↗
NASA NTRS1993

Parametric instabilities of circularly polarized Alfven waves in high-beta plasmas

CGL relations including the effect of finite ion Larmor radius are used to consider a class of parametric instabilities of finite-amplitude, circularly polarized Alfven waves in high-beta plasmas. The disperison relation governing the instabilities is a sixth-order polynomial which is solved numerically. There are two types of instabilities: a modulational instability at k is less than k(0) and a relatively weak and narrow bandwidth instability at k is less than approximately k(0), where k and k(0) are the wavenumbers of the unstable density fluctuation and the 'pump' wave, respectively. It is shown that these instabilities can occur for left-handed pump waves and that the modulational instability is unstable over a very broad band in k with a maximum growth rate at finite k is not equal to 0.

Hamabata, Hiromitsu↗
NASA NTRS1992

Parametric instabilities of large amplitude Alfven waves with obliquely propagating sidebands

This paper presents a brief report on properties of the parametric decay and modulational, filamentation, and magnetoacoustic instabilities of a large amplitude, circularly polarized Alfven wave. We allow the daughter and sideband waves to propagate at an arbitrary angle to the background magnetic field so that the electrostatic and electromagnetic characteristics of these waves are coupled. We investigate the dependance of these instabilities on dispersion, plasma/beta, pump wave amplitude, and propagation angle. Analytical and numerical results are compared with numerical simulations to investigate the full nonlinear evolution of these instabilities.

Vinas, A. F.↗
NASA NTRS1974

Excitation and dissipation of Pc-1 micropulsations

A theoretical model based on hydromagnetic instabilities (including Alfven firehose and magnetoacoustic mirror instabilities), in the region where the electrons are in the transition from collisional to collisionless and ions are in the collisionless region, is proposed as a possible wave emission mechanism for Pc-1 pulsations. The model is compared with recent observations with good agreement between the theory and observations, especially for an emission source located at a distance L less than 5. Furthermore, a suggestion is made that the hydromagnetic instabilities could be relevant to the night and early morning hours emissions while the ion cyclotron instabilities could be responsible for the daytime emission of Pc-1 pulsations.

Hung, R. J.↗
NASA NTRS1992

Alfvenic drift Kelvin-Helmholtz instability in the presence of an equilibrium electric field

The Alfvenic drift Kelvin-Helmholtz instability of a high-beta plasma in the presence of equilibrium magnetic and electric fields perpendicular to each other are studied. The plasma components are assumed to have 2D sheared velocity in y and z directions. The dispersion relation is derived, and the instability criterion is determined. It is shown that the equilibrium electric field has either stabilizing or destabilizing effect depending on certain conditions discussed in the paper.

Sharma, Avadhesh C.↗
NASA NTRS1993

On the dispersion relations for parametric instabilities of parallel-propagating Alfven waves

We consider the dispersion relation for the parametric instabilities of large-amplitude circularly polarized Alfven waves propagating parallel to the ambient magnetic field. A linear perturbation analysis is employed, and the perturbations are taken to propagate along the ambient field. We present an analysis based on Floquet's theorem. The result is a hierarchy of dispersion relations. However, all the dispersion relations are found to be equivalent to the one obtained via the standard analysis; the differences between them are due only to how ca and k are defined. Thus we conclude that physically there is really only one dispersion relation, namely the 'electrostatic dispersion relation', which is in agreement with earlier works. However, we disagree with Vinas and Goldstein (1991), who obtained additional dispersion relations which they have called the 'electromagnetic dispersion relations'. Their additional dispersion relations are a consequence of first truncating the dispersion relation for obliquely propagating perturbations and then taking the limit of parallel-propagating perturbations.

Yajanti, Venku↗
NASA NTRS1978

Modulational instability of finite-amplitude, circularly polarized Alfven waves

The simple theory of the decay instability of Alfven waves is strictly applicable only to a small-amplitude parent wave in a low-beta plasma, but, if the parent wave is circularly polarized, it is possible to analyze the situation without either of these restrictions. Results show that a large-amplitude circularly polarized wave is unstable with respect to decay into three waves, one longitudinal and one transverse wave propagating parallel to the parent wave and one transverse wave propagating antiparallel. The transverse decay products appear at frequencies which are the sum and difference of the frequencies of the parent wave and the longitudinal wave. The decay products are not familiar MHD modes except in the limit of small beta and small amplitude of the parent wave, in which case the decay products are a forward-propagating sound wave and a backward-propagating circularly polarized wave. In this limit the other transverse wave disappears. The effect of finite beta is to reduce the linear growth rate of the instability from the value suggested by the simple theory. Possible applications of these results to the theory of the solar wind are briefly touched upon.

Derby, N. F., Jr.↗
NASA NTRS1985

Nonlinear astrophysical Alfven waves - Onset and outcome of the modulational instability

The nonlinear development of Alfven waves is numerically studied, with applications to Alfven waves in astrophysical plasmas. It is found that amplitude-modulated Alfven wave packets undergo a collapse instability in which the wave packets become more intense and of smaller spatial extent. The wave packet steepening is eventually halted in a process most aptly described as soliton formation. A simple analytic model based on the method of characteristics can account for many of the results of the numerical calculations. The instability probably cannot prevent particle pitch angle isotropization due to self-generated Alfven waves. Nonlinear effects of the collapse may modify the process by which energetic electrons are reaccelerated by plasma turbulence. The model calculations can semiquantitatively account for properties of shock-associated Alfven waves in the solar system.

Spangler, S. R.↗