A new numerical scheme for electromagnetic wave tracing is presented in place of the standard ray-tracing method in studies of electron cyclotron resonance heating. The new method solves the full-wave Maxwell equation, and can take into account wave diffraction, mode conversion (or, cross-polarization scattering), and wave tunneling across an evanescent region between resonance and cutoff layers, in addition to estimating energy absorption due to wave-particle resonances. One and two-dimensional simulations of electromagnetic wave tunneling are also demonstrated.

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The reflectionless transmission of electromagnetic waves in one-dimensional multi-layer plasmas is studied. The wave transmittance is obtained analytically for single-layer underdense plasma as well as for two-layer critical plasma where the wave frequency ω is equal to the electron plasma frequency ω_pe, and it is shown that reflectionless transmission can be possible for both cases. Reflectionless transmission in two-layer critical plasma as well as in single-layer underdense plasma should be considered Fabry-Perot resonance well-known in optics.

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High-speed 2-D imaging of edge fluctuations has been made by a C-MOS camera in Heliotron J. The camera monitored a limiter head, which was inserted into the peripheral plasma. In high-density ECH experiments it was found that the striped patterns of H_α emission near the limiter head periodically shifted along the poloidal direction. The typical spatial length and frequency of this shifted pattern were 8 cm and 5-6 kHz, respectively.

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History of tokamak experiments is briefly reviewed with a special focus on divertors. Two-point divertor model, which calculates plasma parameters up-stream and at the divertor plate for a given condition of particle flux and heat flux, is explained. The model is applied to ITER to discuss the heat flux onto the target plate. The important issues of divertor physics related to recycling, remote radiative cooling, detached plasma and MARFE are also introduced.

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Understanding of the divertor and scrape-off layer (SOL) physics has been progressed during improvements of the compact- and closed-geometry tokamak divertors. Developments of new diagnostics viewing the SOL and upstream of the divertor target (with the finest spatial and⁄or time resolutions) have greatly contributed to establish heat and particle transport models along and across the field lines. Four topics: (i) heat and particle transports upstream of the divertor plate, (ii) burst transport of heat and particles towards the divertor, (iii) SOL plasma flow, and (iv) plasma diffusion in SOL, were reviewed.

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Edge magnetic structures in helical devices are complicated in comparison with those in poloidal divertor tokamaks, resulting in edge transport properties unique to helical devices. The results of experimental observations and computer simulations of the Large Helical Device and Wendelstein7-AS are summarized ; they suggest that cross-field transport plays important role in reduction of plasma pressure along the field lines.

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The numerical modeling of tokamak divertor plasmas and recent related topics have been briefly reviewed. Among the various simulation models, main attention is placed on the fluid model of plasmas and the Monte-Carlo model of neutrals. The following two recent topics are mainly discussed: i) the modeling of excited neutrals and MAR (Molecular Activated Recombination), and ii) plasma flow in the detachment plasma.

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Recent studies using the linear divertor simulators are reviewed. The experimental results regarding detached recombining plasma, convective blobby plasma transport and plasma-material interaction related to tungsten and carbon dusts are reported.

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Three notable experimental results regarding plasma-material interaction between actual tokamak plasmas and high and low Z materials (tungsten and carbon) are reviewed. In the ASDEX-U, a center column was covered by tungsten, and its effects on plasma performance and erosion-redeposition behavior of tungsten were studied. In the TEXTOR, a twin-limiter composed half of tungsten and half of graphite was inserted in the edge plasma to study the difference of plasma material interaction between carbon and tungsten. In the JT-60U, detailed measurements of erosion and redeposition of graphite divertor plates revealed the transport of eroded carbon atoms in edge plasmas.

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This report first discusses the objectives of studies on edge plasma and plasma-wall interaction. Then the projected divertor performance of ITER is presented, and key R&D issues are discussed, including material issues, tritium retention, and transient events such as ELMs and disruptions.

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Present knowledge is reviewed of radiation damage processes in materials. These processes cover various time- and length-scales, from ballistic binary collision process to collective atomic motion in the thermal spike stage, followed by the thermally activated processes involved in defect aggregation. It is emphasized that greater researches are required to understand these processes and their interplay in the multiscale modeling approach, before a prediction of a given material’s response to fusion irradiation conditions is possible. In addition, a predictive capability is also needed to develop new, advanced materials.

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A laser-pumped x-ray laser with full spatial coherence has been developed for the first time. This x-ray laser has a wavelength of 13.9 nm and a beam divergence of 0.2 mrad. In the experiment, a seeding light from the first laser medium was amplified in the second medium, which worked as an active spatial filter. The observed beam divergence was close to the diffraction limited value within a factor of two. The seeding light was amplified in the second medium without refraction influence. The gain region of the second medium was far away from the target surface compared with that of the first medium, and was located in a region of considerably low density. From the measurement of visibility, it was found that the spatial coherent length was longer than the beam diameter. This means that this x-ray laser beam has full spatial coherence.

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Beam driven stable equilibria for a conceptual reactor, Demo-CREST, which was designed for early demonstration of electric power generation, has been investigated. Considering current profiles driven by neutral beams, the attainable normalized beta β_N with a stabilization wall is about 3.4 with a normal shear (NS). With reversed shear (RS), a higher β_N is attainable. The stable equilibria up to 4.0 can be sustained by a couple of On-and Off-axis beams. In the range of 1.9 < β_N < 4.0, power of each beam does not exceed the power in the case of β_N=1.9 which is the base design point of Demo-CREST. In the case of RS operation with β_N=4.0,the density ratio to the Greenwald limit can be maintain at about unity if high temperature operation with T_e>20 keV is allowable.

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The ballooning stability of high beta spherical tokamak(ST) was numerically investigated using 2-D magnetic field measurement of high beta ST in TS-3 ST merging experiment. Numerical analysis of experimental result indicates that the high beta ST produced by two merging STs locates in the boundary region of the first and the second stabilities. Effects of current and pressure profiles on the ballooning stability were studied by varying these profiles artificially around the experimental profiles. The broader pressure profile and the hollower current profiles cause the larger merginal beta value and the wider window region between the first- and the second-stable regions. On the basis of these results, a start-up scenario for ultra-high-beta and second-stable ST was proposed using two merging STs with additional RF heating.

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