A central electron temperature of more than 10 keV is achieved in LHD by 1.2 MW of electron cyclotron heating with a density of 0.6 × 10¹⁹ m^-3. This high temperature is attained by focusing the microwave beam on the resonance near the magnetic axis. The electron temperature prole typically shows steep temperature gradients at the center in this high temperature and low density regime. Non-linear dependences of the central electron temperature on the electron density and the injection power are observed.

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In this short article, significant issues related to the calculations of the opacity of partially ionized atoms are explained in detail. We will mainly pay attention to the treatment of the detailed level structure of low and intermediate Z atoms, based on which the authors are currently developing the opacity code. Some recent advanced treatments of high Z atoms as well as major projects in the world are also briefly reviewed.

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For the purpose of evaluating transient recycling of hydrogen at plasma-facing materials, mass balance equations for mobile and trapped hydrogen atoms have been proposed, in which the elementary processes leading to re-emission, such as diffusion, detrapping, (re)trapping, and local molecular recombination are taken into account. Under appropriate conditions, it was demonstrated that the concentrations of mobile and trapped species can be analytically solved as functions of depth, time, or ion flux, and that the thermal desorption spectrum can be calculated from the time dependence of the concentration of trapped hydrogen atoms. It was also shown that by using the analytical solutions, the diffusion constant and the rate constant of effective local molecular recombinations can be determined experimentally. The experimental data on the diffusion coefficient and the molecular recombination rate are summarized and critically discussed using the solution of the mass balance equations.

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A summary of the recent activities of the plasma-wall interactions database task group at the National Institute for Fusion Science is presented in this report. These activities are focused on the compilation of literature data on key parameters related to wall recycling characteristics that affect dynamic particle balance during plasma discharges and also include on-site tritium inventory. More specifically, this task group has proposed a universal fitting formula and successfully applied it to compile hydrogen implantation-induced retentiondata. Data compilation has been conducted on beryllium, carbon, tungsten, and molybdenum, all currently used for plasma-facing components in magnetic fusion experiments.

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We discuss the present status of the development of computer-simulation hybrid codes that treat both the surface erosion of plasma-facing walls and the diffusion of incident ions and/or of target atoms in those walls, and we also show some simulation results derived by the codes. The codes discussed here are only those that have been developed or used widely in the research field of plasma-wall interactions since 1993.

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A Monte Carlo simulation code, Erosion and Deposition based on a DYnamic model (EDDY), which combines ion reflection and sputtering of plasma-facing materials with transport of released particles in a plasma, is developed. The surface composition change due to impurity deposition, collisional mixing, and thermal diffusion is taken into account. Ionization and dissociation of the released atoms and molecules and their gyromotion are calculated in the plasma. The paper gives an outline of the EDDY code and describes its application to the analysis of particle release from test limiters exposed to the edge plasma of TEXTOR. The calculated results are compared with observations by spectroscopy during the plasma exposure.

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In a moving solid wall divertor system, pebble flow, a falling ball, or a moving belt is used in the plasma-facing component for purposes of load reduction and heat removal. Various processes such as particle exhaust, maintenance, and replacement may be possible in steady state operation via the divertor chamber. With regard to design studies of the innovative moving divertor concept, certain technological issues will be common to almost all cases. In this paper, the heat load, particle control, and operating parameters are described in the case of the pebble divertor system.

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A new cooling concept of free surface flow is proposed as an alternative candidate for the first wall of the self-cooling molten-salt Flibe blanket in the helical-type fusion reactor FFHR. Numerical analyses on capillary flow show that a free surface balanced between surface tension and the forces of wall shear stress and gravity is feasible even in helical systems, where a spiral flow is formed and drastically enhances the heat transfer from the coolant channel wall.

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To provide possible resolution of the technical issues associated with plasma-wall interactions in steady-state magnetic fusion devices, a variety of new concepts of plasma-facing components have recently been proposed. These concepts generally utilize a moving-surface to lower the particle and heat fluxes that result from interactions with edge plasmas. However, the choice of the moving surface varies; in some cases, flowing liquids have been applied, and in others, solids in mechanically controlled motion have been utilized. In this report, the present status of proof of principle experiments on the pebble divertor and rotating drum concepts is presented.

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This article introduces how to process and visualize scientific data with using ”Gnuplot” which is freely available plotting utility from the Internet. Not only a simple example of drawing a single plot on a page but also advanced feature of handling data stream and communication to the external application is explained.

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This tutorial explains how to prepare PDF and PostScript manuscripts for online submissions to journals and e-Print archives using either LATEX or your favorite word-processing software.

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A new compact helical system CHS-qa has been designed based on the advanced stellarator concept of the quasi-axisymmetry in the magnetic field configuration. This new concept of quasi-axisymmetry makes it possible to realize the two-dimensional vacuum magnetic field structure (a tokamak-like configuration) without using plasma current. In this system, the neoclassical transport is greatly reduced compared with conventional helical systems because the helical ripples are very small. Good MHD stability for the interchange and ballooning modes are obtained. The possibility of finding the confinement improvement is also discussed from the viewpoint of plasma rotation and maximum-J criterion.

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