A. S. de Assis

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.

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.

Plasma rotation in toroidal devices with circular cross-sections

The plasma rotation is theoretically investigated in toroidal devices. The dependence of magnetic axis curvature and torsion on the longitudinal coordinate and magnetic field ripples are taken into account. The calculations are carried out within the large aspect ratio and circular magnetic surfaces approximation. General equations for the relaxation of poloidal and toroidal velocities are obtained. The analysis of these equations is completed for the strongly collisional regime (the Pfirsch–Schluter regime). It is shown that, as a result of the relaxation due to the ion parallel viscosity, there is an equilibrium with the ion toroidal velocity equal to zero. The general expression for the ion poloidal velocity in the Pfirsch–Schluter regime is obtained. As in the tokamak case, this velocity is proportional to the ion temperature gradient. It does not depend on the plasma density gradient and on the radial electric field. The problems considered in the paper are of interest, specifically for toroidal devi...

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.

Electron acceleration with kinetic Alfvén waves

It has been studied the quantitative modification of the electron runaway flux due to a spectrum of kinetic Alfven waves (kAw), using the quasilinear (waves) and Fokker-Planck (collisions) equations. It is shown that these modes enhance the runaway production rate via their Cherenkov dissipation. The runaway flux for narrow and broad band spectrum for low and high phase velocities is calculated, and it is found as a general feature that its enhancement is the larger the weaker the background electric field, while for its absolute enhancement it is just the opposite. In some cases, the runaway production rate is found to be enhanced by many orders of magnitude over that without kinetic Alfven waves. It has also been discussed the consequences of this study for cosmic plasmas, namely: amplification of nonthermal emissions from stellar atmospheres, and planetary magnetospheres, (radio frequency waves, and x-ray), life extension of stellar radio bursts, enhancement of Langmuir turbulence, depletion of thermal population in extragalactic jets, and enhancement of auroral electrons precipitation.

On the relaxation of cold electrons and hot ions

The relaxation process of a space uniform plasma composed of cold electrons and one species of hot ions is studied numerically using one- and two-dimensional Landau–Fokker–Planck codes. Relaxation of a monoenergetic ion beam is considered in possibly extreme temperature regimes. Special attention is paid to the deviation of the relaxation process from the classical picture, which is characterized by the close initial temperatures Te≫(me/mi)1/3Ti. The present results give quite a clear idea of the relaxation picture for any initial temperatures also in extreme temperature regimes. A difference scheme, preserving the number of particles and the energy, gives the possibility of solving the problem numerically without error accumulation, except for machine errors.

The perpendicular permittivity of magnetized toroidal plasmas with elliptic magnetic surfaces

The Vlasov equation for charged particles is analyzed in an axially symmetric toroidal plasma configuration with an elliptic cross section of magnetic surfaces. The asymptotic solution of the Vlasov equation is found. The analytical expressions for the perpendicular component of the dielectric permittivity tensor are obtained. These expressions are used for theoretical analyses of the trapped and untrapped ion influence on the collisionless cyclotron 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 ions in tokamak plasmas. It is shown that ion cyclotron resonance dissipation in tokamaks depends on toroidicity and ellipticity parameters and does not depend on plasma temperature.

The Coulomb scattering effect on trapped particles bounce-resonance dissipation in magnetized toroidal plasmas

The solution of the Vlasov equation with a simplified Fokker–Planck collision operator is presented for axially symmetric tokamak plasmas with a circular cross section of magnetic surfaces. The analytical expression for the parallel component of the dielectric permittivity tensor of trapped particles is obtained. This expression is used for theoretical analyses of the collision effect on the bounce-resonance wave dissipation. Conditions for a collisionless description of radio-frequency (rf) oscillations are found. This dielectric tensor components can be used for computer calculations of the rf field structure and the rf dissipated power related to trapped electrons in tokamak plasmas.

Alfvén and fast wave forces, affecting ions in magnetic traps with closed magnetic surfaces

General expressions for time- and surface-averaged radio frequency forces, affecting ions in closed toroidal devices, are obtained in this paper. Toroidal effects are included in these forces. These effects can, for example, be important to calculate Alfven or fast wave forces in stellarators, spheromaks, or for toroidicity induced Alfven wave eigenmodes (TAE) in axially symmetric tokamaks. The further simplification of obtained expressions should be fulfilled for the proper kind of rf waves and toroidal devices. It is hoped that these rf force expressions can, for example, be useful for the computer simulations of the transport barrier formation by Alfven and fast waves in toroidal devices.

Anomalous electron precipitation near the Earth’s auroral zone induced by the wave–particle interaction

The results of a numerical simulation of anomalous electron precipitation in the Earth’s auroral zone induced by waves are discussed. In order to study the plasma electron–wave interaction, a two-dimensional quasilinear code has been used. A quasilinear operator models the electron Landau damping of any plasma eigenmodes: kinetic Alfven waves, whistlers, lower hybrid waves, etc. The distribution function structure was analyzed. The electron current induced by waves, the density, and the plasma energy decay, which stimulates the electron precipitation, have also been investigated.