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The characteristic features of a two-sign point vortex system in positive and negative temperature states are examined by massive numerical simulations using MDGRAPE-2. The temperature is determined by a density of states for a microcanonical ensemble consisting of randomly generated $10^7$ states. Since the density of states has a single peak, the system has negative temperature states. The distributions of vortices in time-asymptotic equilibrium states in positive and negative temperature are obtained by time-development simulations. In positive temperature, both-sign vortices mix with each other and neutralize. In negative temperature, part of the vortices condense and form clumps exclusively consisting of the same-sign vortices, while the other part of the vortices distribute uniformly outside the clumps. It is found that the vortices inside the clumps gain energy and the vortices outside the clumps lose energy to keep the total energy constant. This suggests the common and essential role of the background vortices in the energy-conserving system that assists the formation of the clumps as well as the crystallization and generation of the symmetric configuration observed in the non-neutral plasma experiments.

We study dynamics of discrete vortex strings interacting in a background vorticity distribution by using a magnetized electron plasma confined by a potential distribution in a cylindrical trap, and demonstrate relevant 2-dimensional features characterizing the incompressible dissipation-free guiding-center fluid. Some specific elementary processes are examined and compared with a recently proposed theoretical model that describes a motion of a point vortex moving up a hill of background vorticity distribution. Radial transport of particles is observed to be very limited and associated with several conserved parameters.

Dynamics of two-sign point vortices in positive and negative temperature states is examined by a special-purpose supercomputer (MDGRAPE-2). Temperature T is determined by random sampling of 107 states for microcanonical ensemble in which system energy and angular impulse are kept constant. Distributions of the vortices in time-asymptotic equilibrium state are obtained by time development simulations for various values of T. When T > 0, both-sign vortices mix with each other and neutralize. When T ≪ 0, a part of the vortices condenses and forms the clumps exclusively consisting of the same-sign vortices, while the other part of the vortices distributes outside the clumps uniformly. It is found that the vortices inside the clumps gain energy and the ones outside the clumps lose energy to keep the total energy constant. It suggests the common and essential role of the background vortices in the energy-conserving system that assists the formation of the clumps as well as the crystallization and generation of symmetric configuration observed in the nonneutral plasma experiments.

The field configuration formed by the superposition of a cusped magnetic field and an electrostatic octapole field provides a closed system of confinement for a charged particle. In a cusped magnetic field, the Störmer region which constrains a charged particle is open, but it is closed by adding a potential barrier made by the octapole field. One-component plasmas are thus expected to be confined in this configuration, preserving superior characteristics of the cusp field for plasma stability. A preliminary experiment was performed on the confinement of electrons in this field configuration. An electron plasma was confined for 3 s in a magnetic field as weak as B=50 G at the circular line cusp. The confinement time was roughly proportional to B2, suggesting that the confinement would be improved substantially in a higher magnetic field.

The Alfvén ion cyclotron (AIC) mode is spontaneously excited due to a temperature anisotropy in the ion cyclotron range of frequency (ICRF) heating experiments in the GAMMA10 tandem mirror. The behavior of the AIC mode is studied when the second harmonic electron cyclotron resonance heating is applied additionally. It is confirmed experimentally, that the excitation of the AIC mode is determined solely by the ion pressure and the ion pressure distribution.

The electrostatic potential profile in the outer region of a tandem mirror is calculated by analyzing the ion endloss data which were obtained experimentally. The potential profiles depend on the boundary condition of the position where the potential is zero on the axis. Comparing the calculation with experimental data it is found that the point of maximum potential (plug) does not exist at the outer mirror throat.

As a step towards the creation of a thermal barrier in a tandem mirror, formation of sloshing ion distribution is studied by oblique injection of neutral beams into one of the minimum B mirrors of GAMMA 6. Formation of the sloshing ion distribution is verified from the observations of the pitch angle distribution. The distribution is kept in a quasi-steady state, against relaxation of sloshing ions, to form a broad distribution. Potential dip is also observed in association with the sloshing ion distribution. The potential dip is sustained because the density of cold ions trapped in the dip is small.

An improved directional coupler has been designed, fabricated and tested in order to measure the high-level power of microwave produced by a gyrotron. It has shown a sufficient function requisite in electron cyclotron resonance heating experiments of magnetically confined plasmas. The results of tests under practical experimental conditions are described and various points to be taken in the design of a directional coupler are given.

A sensitive X-ray pinhole camera with microchannel plates (MCPs) has been constructed and successfully used to obtain X-ray images of hot electron distributions produced by electron cyclotron resonance heating in the thermal barrier region of the axisymmetrized tandem mirror GAMMA 10. Tomographic techniques have been applied to reconstruct a 2-dimensional X-ray intensity distribution. It is found that hot electrons are accumulated on the magnetic axis in a disc-like shape with a full width at half maximum (FWHM) diameter of about 25 cm.