Fast frequency sweeping (fast FS) mode in a JT-60U plasma is investigated with particle-magnetohydrodynamic hybrid simulation. A new kind of energetic particle mode (EPM) is found near the plasma center at a frequency close to the central frequency of the fast FS mode. Frequency sweeping close to that of the fast FS mode takes place. The ratio of the mode damping rate to the linear growth rate is consistent with spontaneous hole-clump pair creation.

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The ion kinetic effect on the relaxation of merging spheromaks to a field-reversed configuration (FRC) was studied experimentally using varied S^* (the ratio of the minor radius to the ion skin depth) from 0.5 to 10. The merging spheromaks relax to an FRC (λ_p ˜ 0) or to another spheromak (λ_p ˜ λ_Taylor), depending on whether their initial poloidal eigen value λ_p was smaller or larger than the threshold value λ₀. The varied skin depths of several ion species in the up-scaled experiment revealed that the threshold value λ₀ for the relaxation to an FRC increased inversely with the S^* value. The decrease in S^* promoted the relaxation to an FRC, annihilating the magnetic helicity, in sharp contrast with the conventional Taylor relaxation.

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Recent 70-GHz, 0.4-MW ECH experiments in Heliotron J have revealed the existence of the spontaneous confinement transition, like that of the H-mode, at rather low threshold line-averaged densities of 1.2-1.6 × 10¹⁹ m^-3. The transition was discovered in two edge-iota windows: one is 0.54 < ι(a)/2π < 0.56 at separatrix discharge plasmas and the other is 0.62 < ι(a)/2π < 0.63 at partial walllimiter discharge plasmas. The energy confinement time for the separatrix discharge plasmas was found to be enhanced beyond the normal ISS95 scaling in the transient H-mode phase, being 50% longer than that in the “before transition” phase.

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The status of transport simulation in reversed magnetic shear configuration of tokamaks is described. Based on the turbulent transport model of the current diffusive ballooning mode,the formation of internal transport barrier and the sustainment of reversed shear configuration is examined. The issues in developing the steady state sustainment scenarios are also discussed.

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The formation mechanism of the current hole in tokamak plasmas is reviewed. Experimental results of JT-60U are shown. Increase of the off-central noninductive current is a key factor for the current-hole formation. The internal Transport Barrier (ITB), which generates large bootstrap current, plays an important role. The central current density in the hole stays nearly 0. The idea of a new equilibrium for a tokamak plasma with a current hole is introduced. This equilibrium configuration called ”Axisymmetric Tri-Magnetic-Islands(ATMI) equilibrium”, has three islands along the R direction (a central-negative-current island and side-positive-current islands). The equilibrium is stable with the elongation coils when the current in the ATMI region is limited to a small amount. The confinement properties of a current-hole configuration withbox-type ITB is described. A scaling of the core poloidal beta inside the ITB, β_p,core is given as ε_fβ_p,core ≈ 1,which suggests the equilibrium limit (ε_f : inverse aspect ratio at the ITB foot). Though the core stored energy is little dependent on the heating power, the estimated heat diffusivity in the ITB region moderately correlates with a neoclassical diffusivity.

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The improvement of confinement recently achieved in reversed-field pinch plasmas using the pulsed poloidal current drive technique is presented. It is shown that a relatively small change of the plasma current profile leads to a significant improvement of the energy confinement time, through which better understanding of the energy transport in RFP plasma is possible.

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Though the toroidal current is not indispensable in helical systems, there is a possibility that even small toroidal current extends the operational regimes. In helical plasmas, the various roles of the plasma current are given according to magnetic configurations. We summarize the role of plasma current in some helical configurations. Next we show some examples of experiments in helical plasmas having fairly large plasma current, and discuss the role and the place of the toroidal current in helical plasmas.

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The series of topic articles is summarized. Scenarios of the experiments related with the control of the plasma current profiles and/or the magnetic configuration such as the magnetic shear and the magnetic well are shown as the examples of new viewpoints from experimental research. The new viewpoints from theoretical research are also shown.

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Physics in laser-induced ablation processes are reviewed. The CIP method that can treat the melting and evaporation phenomena is introduced. With the CIP method, the phase transition from solid to liquid and gas can be described very accurately. The comparison with the experiments is made to show the ability of the numerical scheme. The size distribution of nano-particles is compared with experiments.

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Recent progress in linear spectral studies of incompressible plasma (fluid) with flows is reviewed. Mathematically, non-Hermiticity of the generating operator brings about incompleteness of the eigenvalue analysis and unremovable coupling between modes. This may lead to secular growth (algebraic in time) even if all eigenvalues exhibit stable oscillations. Physically, the stretching effect of shear flow is considered a stabilizing mechanism for various plasma instabilities; however, shear flow may equally effectively destabilize a class of plasma modes. The condition for stabilization/destabilization is discussed as well as its physical mechanisms.

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In connection with fast plasma heating in capillary discharges, the transient ionization effect on the plasma conversion efficiency of 4d⁸-4d⁷5p transitions (λ ≈ 13.5 nm) of xenon has been theoretically investigated. Results indicate that ion abundance is a function of the history of plasma evolution, and the fast heating process produces higher conversion efficiency values compared with the steady-state plasma.

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