Shear Alfven Mode Research Articles

Numerical Study on Drift and Alfvén Waves in a Current-Carrying Plasma

A set of coupled eigenmode equations for drift and Alfven modes in a current-carrying stab plasma with magnetic shear is studied numerically. The modes with odd-φ and even- A // parity are investigated where φ and A // are the electrostatic potential and the parallel component of the vector potential of the perturbations, respectively. The shear Alfven mode of this parity is marginally stable for the high β value, and the drift mode of this parity is more stable than that with even-φ and odd- A // parity. Electron-ion collisions are found to stabilize both the modes. The current can not make both the shear Alfven mode and the drift mode unstable. The former remains marginally stable and may contribute to the anomalous transport.

Kinetic Theory of Nonlocal Drift Alfvén Instabilities

Kinetic formulation for linear mode analysis of low frequency shear Alfven mode in low-β plasma is presented. Slab geometry is used with density, temperature and flow velocity varying in the x -direction, and the magnetic shear produced by parallel current is assumed to be sufficiently weak. Integral equation representation in wavenumber space is used in order to take full account of the finite gyroradius and Landau resonance effects. The general formulas derived are applied to two lons wavelength instabilities by reducing integral equations to differential equations in real space; one is the localized drift-Alfven mode instability caused by current density and the other the Alfven mode instability due to ion velocity shear. For the former case, our analysis shows necessity of kinetic effects for instability to occur; for the latter, the lowest order finite gyroradius effect on the stability criterion is investigated.

Numerical Study of Current-Driven Collisional Drift and Alfvén Instabilities in a Sheared Magnetic Field

A set of coupled eigenmode equations for drift and shear Alfven mode in a sheared magnetic field is solved numerically, including effects of the parallel current, the full ion dynamics and electron-ion collisions. Detailed studies are made on the eigenmode structures of both the modes and combined effects of current and finite-β. An outstanding result is that the Current-driven drift mode shows, at some moderate β value, a peculiarity in dispersion and its eigenmode structure is deformed to a shape different from the drift mode one, which means the strong coupling of drift mode to shear Alfven mode due to the combined effects. In the most cases except this, the effects of finite-β and collisions are found to be stabilizing.

Alfven waves and drift compressional modes in multispecies plasmas

The stability of a multispecies plasma under magnetospheric storm conditions is investigated. The dynamics of the impurity ions are incorporated in the hot plasma component response, since the response (to perturbations) of the cold component is totally dominated by the electrons. The coupling between drift compressional and shear Alfven modes is studied in weak and strong coupling limits, the coupling being weakened when a finite fraction of the hot ions belongs to the heavy species. The characteristic growth rates of the mirror instability, modified by the presence of heavy impurity ions, are determined. For the case of strong coupling, the dominant unstable mode is a compressional Alfven oscillation, driven by the finite density gradient of the plasma. The main effect of the impurity ions, in this case, is to stabilize the mode through their inertia. The instability is found to be self‐limiting with increasing plasma pressure, and the asymptotic normalized growth rate is determined.

Macroscopic kink instabilities in toroidal relativistic beams

The interaction of such beams with the shear Alfven modes of the background plasma has been examined and a class of low-frequency instabilities which are similar to the hydrodynamic kink instabilities of the current-carrying plasma have been found. However, for the case of a beam-plasma configuration, the spectrum of the Alfven modes is, in general, complex, which precludes the use of an energy principle. A normal mode approach is employed and both growth rates and real frequencies for n=1, m=1, 2, 3, 4 instabilities for various values of beam energy and nu A/c have been calculated.

Vacuum polarization and photon propagation in a magnetic field

The vacuum polarization tensor in the presence of a static homogeneous magnetic field is calculated exactly as a function of both the magnetic field and the wave vector, and is regularized explicitly by using Shabad’s diagonalization with respect to tensor indices. The wave properties for the two electromagnetic modes in the birefringent vacuum are calculated exactly using a technique from plasma physics. The strongfield limit is considered explicitly and it is shown that the two modes reduce to forms equivalent to the magnetoacoustic and shear Alfven modes in a plasma with Alfven speed much greater than the speed of light.