Pulsating behavior of the ion transport has been discovered in the potential well of a magnetized plasma. Observation of the ion density distribution on a plane perpendicular to the magnetic field reveals that the ion transport pulsation is caused by alternation of ion accumulation and release via a spiral density structure.

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Boronization (boron coating) using diborane was carried out in the Large Helical Device (LHD) for wall conditioning. Using three nozzles for the diborane supply, about 60 % area of the vacuum chamber was covered by boron film. Oxygen impurity radiation was strongly reduced by gettering, and radiation from carbon and metals were reduced about 30 - 40 % by coverage with boron film. As a result, radiation loss was reduced and the operational density exceeded 1×10²⁰ cm^-3, which is about twice of that before boronization.

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Transport evolution in normal and reversed shear JT-60U tokamak plasmas with internal transport barrier (ITB) often occurs via non-local transport bifurcations. In the present paper, we highlight new type of edge-core instantaneous interplay in JT-60U high-β_p plasmas. Abrupt in time (ms timescale) and wide in space (˜0.4 of minor radius) reduction of electron heat flux in the core (ITB-event) is correlated in ms timescale with the start of an ELM that creates enhanced level of H_α. This result gives a hint of the control to form the ITB immediately and non-locally by inducing the ELM-like MHD activity.

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Q machines, which produce low-temperature, stationary and fully-ionized plasmas in magnetic fields, have been operated for over four decades. The results obtained using the Q machine have greatly contributed toward systematizing plasma physics. Their typical examples are the clarification of Landau-damping based linear/nonlinear phenomena on ion acoustic , electron plasma , ion Bernstein waves, etc. , instability phenomena such as drift and ion-cyclotron waves, particle acceleration/heating/transport phenomena, and formation phenomena of charge-nonneutrality induced local electrostatic structure. In addition, transport coefficients in velocity and real spaces have been directly measured in quiescent and turbulent Q machine plasmas. Furthermore, as an extension to technological application, it is tried to control materials structure on nanometer scale using basic properties of the Q machine plasma.

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Construction of double-plasma devices with surface magnetic confinement is shown in detail. Devices have been used for studying various subjects of plasma physics. Experiments on ion-acoustic solitons, multidimensional solitons, oblique collisions of two solitons, ion-beam and plasma interacion, solitary waves in an ion-beam-plasma system, ion-acoustic waves in negative-ion plasmas, double layers, a dusty plasma and chaotic phenomena are briefly described.

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The experimental apparatus for hot-cathode discharge plasmas has made a large contribution to studies of basic plasma physics. Here, we introduce some typical examples in the fields of ion acoustic waves, whistler waves, Alfvén waves, and drift waves.

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The present status of nonneutral plasma science is reviewed with a particular interest in the pursuit of a new frontier for plasma physicists engaged in basic researches. The author does not intend to be exhaustive nor well balanced in the description, but tries to discuss where we are positioned and what we might be able to do to fruitfully enjoy plasma physics and extend its field of activity. Leaving most of topics to the cited references, the author describes characteristic features of nonneutral plasmas appearing in distinct confinement properties, equilibria, transport, nonlinear evolution of Kelvin-Helmholtz instability, and fluid echo phenomena. These examples may convey the significance of nonneutral plasma science as one of newly-rising branches of plasma physics and as a potentially relevant channel through which plasma physics could explore new dimensions.

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Tokamak plasma research has been carried out for more than forty years. Small size tokamaks with major and minor radii of ˜0.3 m and ˜0.1 m were built and used in early experiments, and led the tokamak research to its present successful status involving large tokamaks such as the JT-60U and JET. The role of small tokamaks may have changed, but they still contribute to the understanding of tokamak physics and to the development of tokamak technology. Here, some experimental studies using small tokamaks are shown.

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Experimental techniques of laser ablation are reviewed with the emphasis on diagnostic methods. The current trend of laser sources for ablation experiments is the use of short-wavelength lasers and femtosecond lasers. In addition, several innovations have been tried in the selection of ambient medium of laser ablation. Because of significant spatial distributions with transient properties, the diagnostics of laser ablation plasmas are more difficult than those of discharge plasmas. It is shown that visualized diagnostics are especially useful for the diagnostics of laser ablation plasmas.

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Present status and future prospect of the application of laser ablation phenomena are reviewed, especially focused on the application to the synthesis of functional thin films and nanostructured materials, and to the laser micro-processing using femto-second lasers, hybrid laser processing and other novel methods.

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Glow discharges with different gases in the Large Helical Device (LHD) at the National Institute for Fusion Science (NIFS) show different visual colors of the plasma, and these colors are ascribed to different spectra in the UV and visible wavelength range. From the wavelengths of the observed emission lines, these gases are identified as neon, helium, and hydrogen. The emission line intensity is given by the upper level population density of the corresponding transition via the spontaneous transition probability or Einstein's A coefficient. On the assumption of corona equilibrium, relative emission line intensities of neutral helium are estimated for the n = 3 to n = 2 transitions. The results are in gross disagreement with the glow discharge spectrum. For a single pulsed helium discharge in a Pyrex tube, line emissions are intense during the beginning of the pulse and after the pulse [A. Hirabayashi, et al., Phys. Rev. A 37, 77 (1988)]. The population distribution over the n³ D levels is determined for these two emission peaks, and neither of the results agrees with the expectations from corona equilibrium. It is also found that the color of the plasma observed for a main discharge with helium in LHD is drastically different depending on the plasma condition, and never shows a similar color to that in the glow discharge. All these results indicate breakdown of corona equilibrium and demand us deeper considerations.

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A variational principle is applied to the relaxation of pure electron plasma in a strong axial magnetic field. The initial cylindrical shell structure of electrons can be unstable against Kelvin Helmholtz instability, and the plasma shape relaxes to its final state having a diffused profile. The shape of the plasma distribution in the final state is given based upon the anzats of the minimum enstrophy, and an experimentally-testable formula is obtained.

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Subjects on TRIAM-1M are presented from the viewpoint of plasma physics and reactor technology associated with ‘steady state operation' (SSO). For a future fusion power plant, for burning plasma, complete steady state operation is required. Control of the density under the complicated plasma-wall interaction, non-inductive current start-up, and sustainment of high performance are key areas in the present and future investigations. The following experimental results are reviewed. First, it is shown that the co-deposition of the metallic impurity and oxygen plays an important role in the temporary change in the wall pumping rate, and a model of the co-deposition probability agreed with the observation. It was also noticed that the thermal release of the hydrogen from the plasma-facing components affects the steady state density operation in the ultra long discharge. It was found that enhanced influx of metal impurities from the hotspot affect the steady state operation of the high performance plasma. Second, helium effects on microscopic damage on metals were studied in helium/hydrogen mixture discharges. A large quantity of dislocation loops and dense fine bubbles were observed by means of TEM even for exposure only 125 seconds in duration. From TDS for the specimens, the amount of retained helium was evaluated to be 3.9 × 10²⁰ He/m². Third, the physics understanding for the enhanced current drive (ECD) mode around the threshold power level progressed from the viewpoint of transition probability. The forward transition frequency from a non-ECD plasma state to the ECD state was precisely determined under fixed LHCD power. Thus, a statistical probability for ECD transition was determined; that is, the transition behavior around the threshold power could be described in a statistical manner. Transition frequency showed a strong power dependence. Fourth, the current ramp-up scenario without using centre solenoid coils was reinvestigated at higher density, and controllability of the current ramp-up rate was studied. The plasma was initiated by ECH (fundamental O-mode at 170 GHz with 200 kW) at B = 6.7 T, and a ramp-up rate below the technical limit of 150 kA/s for ITER could be achieved by choosing LH power. A model to describe the ramp-up is proposed.

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