A. G. Elfimov

Coronal loop heating by Alfvén waves

The excitation and dissipation of global and surface Alfvén waves and their conversion into kinetic Alfvén waves have been analyzed for solar coronal loops using a cylindrical model of a magnetized plasma. Also the optimal conditions for coronal loop heating regimes with density of dissipated power ≈103 erg cm−3 s−1 by the new scheme named combined Alfvén wave resonance are found. Combined Alfvén wave heating regime appears when the global Alfvén wave is immersed into the Alfvén continuum with the condition of not-so-sharp distribution of axial current.

Alfvén waves and rotation of collisional plasmas in tokamaks

The effect of radio frequency fields on a plasma rotation in the edge (collisional) region of slightly rippled tokamaks is considered. The expressions for poloidal and toroidal velocities and for quasistationary radial electric fields are obtained as a function of absorbed rf power. The estimations of these quantities for the Phaedrus‐T tokamak [N. Hershkovitz et al., 15th International Atomic Energy Agency Conference on Plasma Physics and Controlled Fusion, Seville, 1994 (International Atomic Energy Agency, Vienna, in press)] are also presented. It is shown that Alfven waves can strongly modify the rotation velocities and radial electric fields in collisional regions of tokamak plasmas.

Hydrodynamic description of Alfvén and fast wave current drive in weakly collisional plasmas of magnetic traps

In this paper, general aspects of the Alfven and fast wave nonresonant and resonant current‐drive problem are considered both for collisional and weakly collisional plasmas. The magnetohydrodynamic approach is used for all collisional regimes and Landau damping is taken into account in the weakly collisional plasma case. Averaged in time and over magnetic surface, the general form of current‐drive forces are derived, including the viscosity and collision frequency perturbation terms. As an example, a weakly collisional plasma cylinder case is discussed and some disagreements on this problem between different authors results are eliminated.

The parallel permittivity of magnetized toroidal plasmas with elliptic magnetic surfaces

The asymptotic solution of the Vlasov equation under the drift approximation, for an axially symmetric toroidal plasma configuration with an elliptic cross section of magnetic surfaces, is presented. The analytical expressions for the parallel component of the dielectric permittivity tensor are obtained. These expressions are used for theoretical analyses of the trapped and untrapped electron influence on the collisionless wave dissipation. The evaluated dielectric tensor components can be used for computer calculations of the radio frequency field structure and the collisionless dissipated power related to trapped and untrapped electrons in tokamak plasmas.

Non-inductive current driven by Alfvén waves in solar coronal loops

It has been shown that Alfvén waves can drive non-inductive current in solar coronal loops via collisional or collisionless damping. Assuming that all the coronal-loop density of dissipated wave power (W= 10−3 erg cm−3 s−1), which is necessary to keep the plasma hot, is due to Alfvén wave electron heating, we have estimated the axial current density driven by Alfvén waves to be 〈jz〉 ≈ 103–105 statA cm−2. This current can indeed support the quasi-stationary equilibrium and stability of coronal loops and create the poloidal magnetic field up to Bθ≈1−5 G.

Dielectric permeability of a mirror-trapped plasma

Analytical expressions for the wave permeability tensor are derived for a two-dimensional plasma model of a straight axisymmetric mirror trap. The dielectric tensor components are found through a solution of the Vlasov equation, using the theory of Jacobian elliptic functions. The bounce-resonance effect of trapped particles on wave dissipation is analysed. It is shown that collisionless wave dissipation in the plasma with a mirror-trap configuration of a magnetic field can differ essentially from Landau damping in a plasma with straight uniform magnetic field lines. This dielectric tensor can be used in numerical calculations of Alfven and ion cyclotron heating of mirror-trap plasmas.

The permittivity tensor and bounce resonance effects on wave dissipation in toroidal plasmas

The asymptotic solution of Vlasovs equation in the drift approximation for a toroidal plasma geometry with circular magnetic surfaces is presented. The method of solution introduces Jacobi functions as variables, making it possible to obtain results in a relatively simple manner. The analytic evaluation of the parallel components of the dielectric permittivity tensorε3j is shown and the resulting strong influence of the bounce resonance of untrapped electrons on the wave dissipation is discussed. Additionally, a numerical calculation ofε33, together with a comparison between the toroidal and the cylindrical (Landau damping) results, are presented.

Rotation of weakly collisional plasmas in tokamaks, operated with Alfvén waves

The effect of the kinetic Alfven waves on weakly collisional plasma rotation in tokamaks has been studied for the plateau and banana regimes. The quasistationary rotation velocities and radial electric field have been found. The estimation of these quantities for the Phaedrus‐T tokamak [S. Wukitch et al., Phys. Rev. Lett. 77, 294 (1996)] and for the Joint European Torus (JET) [A. Fasoli et al., Nucl. Fusion, 36, 258 (1996)] has been presented. It is shown that the kinetic Alfven waves, which are needed for current drive, change weakly the quasistationary rotation velocities and radial electric field, as found from the experimental data of these tokamaks. In conditions with increased rf power, the plasma rotation and radial electric field can essentially grow up.

Influence of trapped electrons on the dielectric properties of the Earth’s radiation belts

The dielectric tensor of an axisymmetric magnetosphere is derived by solving the Vlasov equations for trapped particles for a two‐dimensional plasma model with circular magnetic field lines. Because of the nonuniformity of the geomagnetic field any Fourier harmonic of the perturbed current density (after its Fourier expansion over the geomagnetic latitude) is proportional to the sum over all harmonics of the oscillating electric field; that leads to additional wave dissipation effects. The resonant conditions for wave–particle interactions are discussed taking into account the cyclotron and bounce resonances; these conditions in magnetospheric plasmas are entirely different from the Landau damping resonant factor in the uniform magnetic field. The numerical calculations of the longitudinal permeability in the Earth’s radiation belts (the equatorial distance of the magnetic field line is five Earth’s radii) are carried out for short‐period oscillations with the frequency ω∼2 s−1 and longitudinal wave numbe...

Noninductive current generation by Alfvén wave-electron interaction in solar loops

It is shown that Alfven waves can drive non inductive current in solar coronal loops via Landau damping. Assuming that all the coronal loop density of dissipated RF power (P = 10-3 erg/cm 3 s-1) necessary to keep the plasma hot is due to Alfven electron heating, we have estimated the axial current drive density to be jz ≈ 103 st A/cm2. This current can indeed support the quasi-stationary equilibrium of coronal loops and create the observed poloidal magnetic field of B ≈ 10 G.