Table of contents

Experimental studies of the formation, equilibrium and stability of a linear Extrap Z-pinch are reported. The Z-pinch discharge is generated between electrodes along the Z-axis of a linear octupole field produced by currents in four Z-directed rods. The combined discharge current and rod currents produce a magnetic field having a separatrix with four null X-points which define the corners of a square-shaped region where the high beta plasma discharge is contained. Bounding the pinch discharge with a separatrix produces equilibria which are stable against global kink modes for the 50- mu s duration of the discharge which corresponds to about 100 Alfven transit times. The equilibria, with line densities of about 3*10¹⁸ m^-1, are consistent in magnitude and scaling with the Bennett relation.

Radial profiles of plasma rotation frequency and particle temperatures in a hollow cathode argon discharge with superimposed magnetic field have been spectroscopically measured. The results are compared with theoretical models. A model based on non-ideal MHD equations is shown to give the best fit to the experimental results. Methods to evaluate proper radial profiles of temperature, emissivity and rotation frequency from Doppler-shifted side-on measurements are derived in the Appendix.

A general kinetic formulation is developed for the transport of neutrals in a multicomponent cool plasma mantle. Analytical expressions are obtained for the neutral density profiles. It is found that for a dense plasma mantle the neutral density is determined by recombination and has a value which is orders of magnitudes higher than in the absence of recombination. For a low density plasma mantle the impurity neutral density inside the mantle is determined by mutual charge exchange and its profile has the same shape as that of hydrogen neutrals.

The influence of fast primary electrons on the leak width of a plasma in a picket fence or cusp geometry in the presence of a neutral gas background is discussed theoretically. Without primary electrons a leak width of the order of an ion Larmor radius (a_i) is found, whereas with fast primary electrons a leak width of the order of a hybrid width (2 square root a_ia_e) can be obtained. This is in agreement with experimental data in the literature.

The lowest order kinetic effects are included in the equations for nonlinear electrostatic electron waves in a magnetized plasma. The modifications of the authors' previous analysis based on a fluid model are discussed.

The interaction between two ion acoustic solitons, propagating in the same direction, via reflected ions and the amplification of the trailing waves behind the front soliton are experimentally studied using a technique of double-pulse excitation.

Cyclotron resonance heating rates are found for a parabolic magnetic mirror. The equation of motion for perpendicular velocity is solved, including the radial magnetic field terms neglected in earlier papers. The expression for heating rate involves an infinite series of Anger's and Weber's functions, compared with a single term for the unrevised expression. The new results show an increase of heating rate compared with previous results. A simple expression is given for the ratio of the heating rates.

It is shown that the suppression of standing ion-waves appearing in a single ended Q-machine plasma by applying a positive DC bias to an exciting electrode can be achieved by modifying the negative space charge formed close to this electrode, using positive ions. This experimental result is accounted for by change of the reflecting properties of above mentioned space charge.

Since the photons transfer momentum much more efficiently to electrons through Thomson scattering, selective acceleration of electrons will take place in an anisotropic radiation field, thus contributing to an electric current generation. The authors consider an optically thick, fully ionized, hydrogen plasma with the temperature gradient (dT/dZ) and the velocity shear (dV_x/dZ) in a slab geometry (no spatial dependence in x- and y-directions). They calculate the current generation rate in the direction of the plasma flow velocity (x-direction) as the function of dT/dZ and dV_x/dZ.

Neutralized, rippled, magnetically focused electron beams are found to be unstable against surface space charge waves. The instability proceeds through the coupling of slow and fast waves, rather than through that of two fast or two slow waves.

The nonlinear interaction of drift-tearing modes in the presence of an electrostatic drift wave turbulence background is investigated. The authors assume that the interaction is significant only when the magnetic islands of the modes overlap sufficiently. It is found that there exist fast growing nonlinear instabilities driven by an effective (turbulent) electron viscosity, which may be orders of magnitude larger than the fluid viscosity.