Table of contents

Nonlinear Alfven waves, propagating along an equilibrium magnetic field, are studied on the base of relativistic isotropic hydrodynamics. Alfven solitons of moving-wave and wave-packet type are considered. The results of Sakai and Kawata (1980) concerning the Alfven solitons of moving-wave type are revised. New expressions for the parameters characterizing these solitons are obtained.

For pt.I see ibid., vol.27, no.5, p.527-37 (1985). Kinetic theory of nonlinear Alfven waves propagating along the equilibrium magnetic field in a relativistic electron-positron plasma is presented. Comparison of the results of kinetic and hydrodynamic approaches is performed. Excitation of the Alfven solitons by a beam of high-energy particles is discussed. Results obtained are used for the interpretation of the microstructure of radio radiation of pulsars.

For the detection of plasma density fluctuations where the wavelength is too large for traditional Bragg scattering, two techniques have been suggested; phase scintillation and far forward scattering. It is shown in this paper that these techniques are not fundamentally different; they correspond respectively to near field and far field detection of electromagnetic radiation diffracted by the density fluctuations.

Localized resistive modes (resistive interchange and resistive ballooning modes) are investigated for self-consistent Tokamak equilibria which have circular cross-sections near the magnetic axis. The second region of stability (which is stable with respect to ideal ballooning modes at high poloidal beta beta _p) proves to be unstable when resistive effects are taken into account as well. In the low beta _p stability region, the stability boundaries are shifted toward lower beta _p values. The magnitude of the shift depends on the degree of localization of the perturbation around the field line, highly localized perturbations being the most unstable ones.

A numerical analysis of nonlinear behavior of m=1 resistive internal kink instability in a Tokamak is presented in a cylindrical approximation. A two-dimensional nonlinear code which solves incompressible resistive MHD equations with helical symmetry has been developed. For the case of small longitudinal wave number k, the magnetic axis moves outward until it reaches the critical surface where the value of helical magnetic flux has the same value as the one at the magnetic axis. On the other hand, as k is increased, the shift of the magnetic axis saturates before touching this critical surface. This result gives a possible explanation of suppression of internal disruptions observed in high power neutral beam injection experiment to Tokamaks.

Plasma surface waves are excited by a high frequency field in a semi-infinite plasma with a plane boundary when omega ₀- omega _p approximately=+or-( omega _p/ square root 2) and omega ₀- omega _p approximately=+or-( omega _p square root 2)- omega ₀ ( omega ₀ being the frequency of the high frequency field and omega _p the plasma frequency). The instabilities, in effect, take place at (n_c/n₀)=3, 8.5*10^-2, 0.72 and 2*10^-2, where n_c and n₀ are the critical and the particle densities respectively. Threshold conditions are derived for plasmas with and without a low density electron beam. In the absence of the beam the thresholds are more than the relativistic limit while its presence reduces the thresholds considerably under certain conditions.

An schlieren method with sub-millimeter and sub-nanosecond resolution was used to investigate profile variations of a fast collapsing focus plasma. Computer simulations allowed the authors to trace rays through the plasma and the schlieren system to the film plane where they produce intensity distributions which depend on density profiles of the plasma. In matching simulated intensity distributions to experimentally produced schlieren pictures, parameter ranges for density, density gradients and sheath thickness have been determined.