Masatomo Sato

On the Stability of a Magnetically Compressed Plasma Surface

An attempt to show that the occurrence of RayleighTaylor (R-T) instabilities depends on the magnitude of the initial rising rate of the magnetic field, B = (dB/dt), if other experimental conditions are the same, is presented. The inertia force driving instability and the resistive damping decrease, in effect, with increasing B. The absence of instabilities is due to lower values of B. Data are presented in tabular form, and discrepancies are discussed. (L.N.N.)

On The Solitary Vortex Solutions of Nonlinear Drift Wave Equations

The Hasegawa-Mima equation for a quasi-two-dimensional electrostatic drift wave is generalized to include arbitrary distributions of the equilibrium electrostatic potential and the density and temperature of plasma. It is shown that the spatial dependence of the equilibrium density distribution plays a decisive role in determining the behavior of the steady vortex solution, that is, whether it is a single soliton or pair-solitons, etc. The relation between the drift wave equation and the barotropic equation for Rossby waves is discussed, and, in particular, a remark is made on Petviashvilis equation which has an additional nonliruear term proportional to the temperature gradient.

Stationary drift-rossby vortices in shear flows

Stationary vortex solutions of the Charney-Hasegawa-Mima equation describing planetary Rossby waves and plasma drift waves are analyzed for background flow with velocity shear. The solutions are obtained by Larichev-Rezniks method that divides the entire plane into two regions by a circle on which the internal and external solutions of linear equations are connected. The boundary conditions on the circle are satisfied correctly by adding a vorticity-free flow to the external background shear flow. Explicit flow patterns, dipolar, tripolar and quadrupolar, are given for several kinds of the background shear flows; the monopolar vortex like the Jovian Red Spot could not be obtained by this method. Another method is given, to derive a nonlinear equation for the stream function when the equilibrium density profile and shear flow in a plasma are prescribed.

Expansion and Thermalization of Plasma in a Non-Uniform Magnetic Channel

Theoretical investigations of the unsteady motion of plasma in a magnetic channel are made on the basis of the hydromagnetic theory of an ideal fluid. A set of one dimensional equations on which the investigations are made is derived in the near-axis approximation from three dimensional equations. Using these equations dynamical expansion of an initially uniform plasma at rest contained in a region of strong magnetic field into a region of weaker field, and shock thermalization of the expanding plasma on colliding with a rigid wall (or with another flow in the opposite direction) or being decelerated by a magnetic barrier are investigated. Analyses are made both analytically and numerically.

Influence of Dust-Charge Fluctuation on Coherent Structures in Magnetized, Inhomogeneous Dusty Plasmas

In dusty plasmas, the fluctuation of charge on dust grains may have a significant influence on collective phenomena in the plasma. We study this dust charging effect on the electrostatic drift flow in dusty plasmas paying particular attention to the formation of quasi-stationary coherent structures. Two regimes of different time scales, the ion-drift regime and the dust-drift regime of much lower frequency, are considered by deriving for each regime a pair of coupled equations describing the temporal change of the stream function of drift flow and the dust-charge fluctuation. For both regimes, the current to dust grains must be small enough to yield a quasi-stationary flow. In the case of ion-drift flow, the small current is consistent with the low level excitation of the charge fluctuation, giving no appreciable influence on the coherent structure. In dust-drift flow, the charge fluctuation with a finite amplitude may behave in phase with the potential, acting to reduce the increase of the propagation sp...

The Velocity Distribution Function of Thermonuclear Alpha Particles in a Mirror Reactor

The velocity distribution of α-particles produced by D-T reactions in a magnetic mirror reactor is analyzed using the Fokker-Planck equation, which is integrated numerically after expanding the distribution function of α-particles in a series of eigenfunctions of the Legendre equation. Together with the distribution function, several quantities of interest are then evaluated. The influence of the velocity distributions of plasma electrons and ions on the α-particles is investigated by assuming two model functions, Maxwellian and non-Maxwellian, and it is shown that the form of the electron distribution at low speeds may have important effect on the α-particle distribution. The convergence property of the Legendre expansion is also discussed.

Rossby Wave Equation for Long Wavelength

It is well known that the nonlinear Rossby wave equation has a dipole vortex solution, the so-called modon, in the short-wavelength regime. For a steady state in the long-wavelength regime, we find an appropriate variable transformation to express the potential vorticity in conservation form, and obtain a nonlinear Schrodinger equation for the stream function. It is found by numerical analysis that the equation has a monopole vortex solution for small separatrix radius.

Breakdown Condition in an Azimuthal Discharge

The condition of the gas breakdown is investigated. Two distinct types were found. One is accompanied with a full production and subsequent contraction of plasma; in the other are glow discharges without the full plasma production. The former was observed by photomultiplier measurement of the light intensity, high-speed camera observation of the plasma contraction, and the particular deviation and enhanced decay rate of the voltage oscillogram from the natural one.

Instability of Alfvén Waves by Fast Ions in a Plasma in a Magnetic Mirror Field

The instability of Alfven waves by fast ions in a plasma in a magnetic mirror field is investigated theoretically taking explicitly into account the bounce motion of the fast ions between turning points. The linear growth rate of instability is calculated and the result is compared with the result obtained by the usual theory which assumes free motion of particles. In the case of a nearly mono-energetic velocity distribution of fast ions, with the velocity spread equal to the thermal velocity of the host plasma ions, the maxumum growth rate by the bounce-motion theory is reduced by the factor (fast-ion energy/host-ion temperature) 1/4 from that by the free-motion theory. The difference is less remarkable in the case of a broad distribution of fast ions.

High Frequency Electrostatic Instabilities in a Plasma with a Small Fraction of Hot Electrons

The electrostatic instabilities with frequencies close to the integral multiples of the electron gyrofrequency (\(\varOmega\)) are considered for a plasma in a uniform magnetic field, where the plasma is composed of a small fraction of hot electrons of “loss-cone” type velocity distribution and a cold main body. The instabilities are produced as a result of the coupling between the electron-cyclotron wave of the hot electrons and the upper-hybrid mode of the cold plasma. It is found that among the length hydrodynamic and the kinetic modes considered, the short wavelength hydrodynamic “flute” mode with the frequency 2\(\varOmega\) is the most probable one for the experimental conditions of the hot electron plasma formation in a slow theta-pinch.