Table of contents

Experimental results are presented which show that r.f. power at frequencies near the lower hybrid frequency couples resonantly into a standing whistler wave. For an input power flux of less than 5 W cm^-2 densities above 10¹² cm^-3 with close to 100% ionization have been achieved. Measured density, temperatures and wave fields are presented and are used as input parameters for a theoretical model.

Thermal non-equilibrium in a preionized argon plasma kept between two plane parallel plates in the presence of an applied electric field parallel to the surface is investigated theoretically. A multifluid theory is formulated taking into consideration the kinetics of sheath region formed near the surface. With the local transport properties accurately evaluated from kinetic theory, the system of equations is solved numerically. The influence of various parameters on thermal non-equilibrium characteristics is studied. The present study reveals substantial deviations from LTE in the regions near the wall at lower currents. Of the several modes of energy transfer mechanisms identified near the wall, the heat conduction of heavy particles is found to be the dominating one. Numerical experiments show that both electron temperature gradient and electron energy flux at the wall are negligible and consequently in all multifluid analysis it is proposed that the electron subgas may be taken as thermally insulated at the boundaries.

Two-dimensional, collision free, z-independent equilibria of a high- beta plasma in an external magnetic field are studied, using distributions of the form f(H,p_z). The charge-neutral approximation then makes the macroscopic moments and the electrostatic potential functions of the magnetic vector potential A only, whereby these quantities assume constant values along the magnetic field lines, and the treatment becomes essentially one-dimensional with the use of flux coordinates. MHD-like equations of simple form for both particle species are obtained, including both an ambipolar electric field, arbitrarily large gyro excursions and lines with zero magnetic field component in the (r, theta ) plane. These equations provide useful interrelations between the macroscopic quantities that may be of value for interpretation of experimental results. A parametrized subclass of distributions gives a flexible tool for constructing solutions corresponding to given macroscopic profiles, and an expression for the smallest obtainable pinch radius is derived. An alternative to free-boundary methods for computing the magnetic field is presented. Intended applications concern linear and large aspect ratio toroidal systems of z pinch and multipole type.

Previously-introduced methods for analytically estimating the effects of small-scale turbulent fluctuations on large-scale dynamics are extended to fully three-dimensional magnetohydrodynamics. The problem becomes algebraically tractable in the presence of sufficiently large spectral gaps. The calculation generalizes 'alpha dynamo' calculations, except that the velocity fluctuations and magnetic fluctuations are treated on an independent and equal footing. Earlier expressions for the 'alpha coefficients' of turbulent magnetic field amplification are recovered as a special case.

The purpose of this paper is to indicate theoretically how much the magnetic field influences the collision frequency for the nuclear fusion reaction. Since the Larmor radius, r_L, of a particle in a usual magnetic field strength is large compared to the radius of the cross section, sigma , for the nuclear fusion reaction, the magnetic field does not affect the cross section. However, due to the gyration of the particle during a free path, the relative velocity is affected. First, the flow of charged particles across an area sigma per unit time is obtained, and then the collision frequency in the presence of the magnetic field is determined. It is shown that when 2 pi r_L is small compared with the mean free path lambda , the velocity component contribution to the collision is the velocity component due to the motion along the field axis and not that due to the gyration.

The influence of an RF pump wave on the spectral electric field fluctuation density and the value of the electromagnetic wave energy density, which is absorbed in the presence of parametric instabilities, is investigated. The RF field power which is absorbed in the plasma is estimated near the threshold of the decay instability. It is shown that the absorbed power increases anomalously as ln(E_th,1²/E₀²-1) for the decay of pump wave into lower hybrid and ion-acoustic waves and as (E_th,2²/E₀²-1)^-1/2 for the decay of pump wave into lower hybrid wave and ion quasimode (E_th,1 and E_th,2 are the threshold electric field strength relatively to the excitation of the instabilities which are under consideration and E₀ is the pump field strength).

This paper draws attention to some mechanisms which can contribute to the understanding of particle transport in Tokamaks and similar systems. First, it is demonstrated that, even when there are highly anomalous heat losses due to electron heat conduction, the particle losses do not necessarily have to become strongly anomalous but can remain nearly neoclassical. Second, plasma-neutral gas interaction is shown to have a number of important effects on plasma equilibrium, transport and profile shaping, even in Tokamaks where the boundary layer only contains a small fraction of neutral particles. Thus, under rather general conditions of strong recycling, the characteristic plasma pressure gradient in the boundary layer becomes independent of the rate of particle transport. On the other hand, the ratio between the average electron density and the neutral density at the plasma edge provides a measure of the plasma particle loss rate. Finally, in Tokamaks near the density limit, the heat losses due to plasma-neutral gas interaction affect the energy confinement time. The present analysis appears to be consistent with experiments, as far as orders of magnitude are concerned.

Solitary wave excitation by applying a negative potential pulse in a double plasma device is experimentally studied. Results indicate that the system used here is free from the effects of burst ions, which are unavoidable in the case of positive pulse application.

Experimental data are presented to show that the use of the dispersion relationships, which are derived from the steady state solutions of the hydromagnetic equations governing the plasma, for the interpretation of transiently excited Alfven waves is not a valid procedure. The most serious misinterpretations can occur near the wave guide cut-off for the fast wave since the complex wave number represents strong absorption and the group velocity ceases to have a clear physical meaning.