[en] Collisionless tearing instabilities and the associated electron heat transport are investigated by using a two-and-one-half dimensional particle simulation code. It is shown that a collisionless drift tearing instability saturates at a low amplitude and turns into a nonlinear pure tearing instability. The electron internal energy profile is flattened within the magnetic island. The electron heat conductivity obtained from the heat flow across the singular surface is proportional to W⁴ in the linear phase and to (dW/dt)W² in the nonlinear phase of the tearing instability. Here W is the half width of the magnetic island. A theoretical model to explain these results is also presented. (author)

[en] Collisionless tearing modes and the enhanced transport associated with this instability are investigated theoretically and by using a two-and-one-half dimensional particle simulation code in a slab geometry. The effects of electrostatic fields on the instability are also considered. The initial current is found to diffuse along the perturbed magnetic field lines with the observed diffusion coefficient in good agreement with the theoretical prediction. Electrostatic effects have a tendency to enhance the tearing mode growth rate. The growth of the mode is observed to divide into three phases. In multi-mode tearing, a combination of magnetic islands is observed. (author)

[en] The Large Helical device (LHD), now under construction is a Heliotron/torsatron device with a closed divertor system. The LHD divertor magnetic structure has been studied in detail. A peculiar feature of the configuration is the existence of edge surface layers, a complicated three dimensional magnetic structure. However it does not seem to hamper the expected divertor functions. As a confinement improvement scheme in LHD, we have proposed a high temperature divertor plasma operation in which a divertor plasma with a temperature of a few kev, generated by efficient pumping, leads to the confinement improvement. (author)

[en] Tandem mirror Gamma 10 employs a thermal barrier to insulate the electrons in the end plugs from those in the central cell. Generation of the thermal barrier in Gamma 10 requires the creation of a hot mirror trapped electron population, heated by electron cyclotron resonance heating. We calculate creation of the hot electron population when only second harmonic electron cyclotron resonance heating is included in the thermal barrier region. We then calculate the plug and thermal barrier potential formation when fundamental electron heating and neutral beam injection are added, using our bounce averaged Fokker-Planck code. To study the hot electron build up in the thermal barrier region theoretically and numerically, we include the quasilinear electron heating effects in the Fokker-Planck equation. (Mori, K.)

[en] A mirror magnetic field configuration (MFC) is studied in which a divertor is distributed axially using multipole coils. Both configurations of divertor and minimum-B are obtained in a mirror cell. Magnetohydrodynamic (MHD) instability of a mirror cell can be eliminated in this way. Concept of the design and properties of the MFC are discussed

[en] GAMMA 10 is an axisymmetrized tandem mirror with minimum-B-MHD anchors and outboard thermal barriers. The design, fabrication and testing of GAMMA 10 device are described. Magnetic-field analysis and structural analysis were made and new fabrication method were adopted in order to obtain a magnetic field configuration with high precision and reliability. The error field in the plasma region is less than 0.2% of the designed value. (author)

[en] We have studied the hot electron build-up by the second harmonic electron cyclotron resonance heating in the thermal barrier region of tandem mirror GAMMA 10 by using a Fokker-Planck code with self-consistent potential profile taken into account. We have found two phases in the evolution of hot electron population and the potential profile. In the first phase where the RF diffusion is dominant quick increase of the hot electron density and that of the mean energy are observed. No further increase in the mean energy is observed thereafter. The potential is the deepest during the first phase. The second phase starts in the mean-free-time of the pitch angle scattering of hot electrons on cold electrons and ions. In this phase the hot electron population increases in the rate of the pitch angle scattering. The potential dip shallows due to the accumulation of pitch angle scattered passing ions. This observation indicates the necessity of the ion pumping for maintaining the negative potential at the thermal barrier. (author)

[en] The authors have studied the hot electron build-up by the second harmonic electron cyclotron resonance heating in the thermal barrier-region of tandem mirror GAMMA 10 by using a Fokker-Planck code with self-consistent potential profile taken into account. The authors have found two phases in the evolution of hot electron population and the potential profile. In the first phase where the RF diffusion is dominant quick increase of the hot electron density and that of the mean energy are observed. No further increase in the mean energy is observed thereafter. The potential is the deepest during the first phase. The second phase starts in the mean-free-time of the pitch angle scattering of hot electrons on cold electrons and ions. In this phase the hot electron population increases in the rate of the pitch angle scattering. The potential dip shallows due to the accumulation of pitch angle scattered passing ions. This observation indicates the necessity of the ion pumping for maintaining the negative potential at the thermal barrier

[en] We have studied the hot electron build-up by the second harmonic electron cyclotron resonance heating in the thermal barrier region of tandem mirror GAMMA 10 by using a Fokker-Planck code with self-consistent potential profile taken into account. We have found two phases in the evolution of hot electron population and the potential profile. In the first phase where the RF diffusion is dominant quick increase of the hot electron density and that of the mean energy are observed. No further increase in the mean energy is observed thereafter. The potential is the deepest during the first phase. The second phase starts in the mean-free-time of the pitch angle scattering of hot electrons on cold electrons and ions. In this phase the hot electron population increases in the rate of the pitch angle scattering. The potential dip shallows due to the accumulation of pitch angle scattered passing ions. This observation indicates the necessity of the ion pumping for maintaining the negative potential at the thermal barrier. (author)

[en] The neoclassical resonant plateau transport in a mirror cell is studied theoretically. The analytical expression for a non-square-well magnetic field is obtained. The analytical result is applied to the GAMMA10 tandem mirror [T. Cho, M. Yoshida, J. Kohagura et al., Phys. Rev. Lett. 94, 085002-1 (2005)], which consists of several mirror cells in it, and the confinement time due to the neoclassical resonant plateau transport is determined in each mirror cell. It is found that the neoclassical resonant transport of ions trapped in the nonaxisymmetric anchor mirror cell and transition mirror cells is significantly smaller than those trapped in the central cell