We constructed a collisional-radiative model including doubly excited states for a two electron ion. We study the density effects on the effective rate coefficients and the n-dependence of the population densities where n is the principal quantum number. The effective 1s-2l excitation rate coefficients increase with increasing electron density due to the indirect process. We also found that for 2s-1s de-excitation,l-changing transitions, 2snl-2pnl, are important at intermediate densities. The population densities per statistical weight for doubly excited states attain a scale of n^-4 at very high density in ionizing plasmas.

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The dynamics of plasma and the reversal flow of neutral particle are investigated experimentally in a closed-divertor simulator. It is observed that the ionized front periodically moves in and out of the closed divertor region, as the neutral gas is injected sufficient amount for achieving plasma detachment in the divertor region. Such movement can be related to the reversal flow of the neutral particles injected.

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New trend is described on the basis of previous and on-going achievements. Magnetic shear is effective to stabilize ideal interchange modes, on the other hand magnetic well is needed for stabilization of resistive modes and micro-instabilities. Owing to recent developments in numerical tools on optimization of magnetic surface quantities it is now possible to construct magnetic surfaces that can satisfy requirements from reactor considerations. Confinement improvement and divertor capability might be an important theme in the near future.

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Quasi-symmetry concepts in helical systems are briefly explained. The one of the magnetic coordinates, Boozer coordinates, are the essential basis for considering quasi-symmetry concepts in terms of drift trajectories and neoclassical transport properties. Several features of quasi-symmetric (quasi-axisymmetric, helically symmetric and poloidally symmetric) concept are briefly described from the viewpoints of configurational properties. The intuitive classification of these concepts (including (quasi-)isodynamic concept) is also given.

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Plasmas have been formed in the Helically Symmetric Experiment (HSX) using second harmonic ECH from a 28 GHz gyrotron. The plasma breakdown time is symmetric with respect to resonance location in the Quasi-Helically Symmetric (QHS) configuration. Addition of a mirror term to the spectrum introduces a strong asymmetry, with longer times required with low-field side resonance. Asymmetries are also observed in the stored energy as a function of heating location in the mirror mode. At low densities, improved confinement is observed for the QHS mode as compared to the mirror mode as inferred from absorbed power and the presence of an energetic electron population.

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Compact quasi-axisymmetric stellarators offer the possibility of combining the steady-state low-recirculating power, external control, and disruption resilience of previous stellarators with the low-aspect ratio, high beta-limit, and good confinement of advanced tokamaks. Quasi-axisymmetric equilibria have been developed for the proposed National Compact Stellarator Experiment (NCSX) with average aspect ratio ˜4.4 and average elongation ˜1.8. Even with bootstrap-current consistent profiles, they are passively stable to the ballooning, kink, vertical, Mercier, and neoclassical-tearing modes for β = 4%, without the need for external feedback or conducting walls. The bootstrap current generates only 1/4 of the magnetic rotational transform at β = 4% (the rest is from the coils). Transport simulations show adequate fast-ion confinement and thermal neoclassical transport similar to equivalent tokamaks. Modular coils have been designed which reproduce the physics properties, provide good flux surfaces, and allow flexible variation of the plasma shape to control the predicted MHD stability and transport properties.

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A low aspect ratio helical device CHS-qa has been designed based on the quasi-axisymmetric configuration which is one of the new advanced stellarator concepts. As the basic necessary conditions for the new confinement experiment, ideal MHD stability has been examined for the Mercier, ballooning and kink stability criteria. A good quasi-axisymmetry was also realized keeping the good stability condition. As well as making efforts to reduce the neoclassical transport based on the quasi-axisymmetry, various considerations were made with respect to the experimental study of the improved confinement of helical systems from the viewpoint of the anomalous transport. In addition to the main modular coils, auxiliary coil systems are designed to give flexibility of the magnetic field configuration in CHS-qa, which are important to make good experimental study of the confinement physics.

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Physics designs of NCSX and CHS-qa are compared. Although those are basically of similar magnetic configuration the important difference is in the role of the bootstrap current. Different toroidal period numbers make the aspect ratio and the machine design different.

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This article shows the useful tools on personal computers. The electronical dictionaries, the full-text search system, the simple usage of the preprint server, and the numeric computation language for applications in engineering and science are introduced.

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In order to establish the applicability conditions of incoherent laser Thomson scattering (LTS) for plasma diagnostics of electron properties to various kinds of discharge plasmas, a method of approach was discussed, and criteria for applicability were established. These criteria were then applied to three representative discharge plasmas: inductively coupled plasmas (ICP) in Ar/CF₄ and Ar/O₂ gases, and a microwave-produced plasma in a H₂/CH₄ gas. Implications of the results are discussed.

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Compact x-ray lasers are being developed by transient collisional excitation method using a CPA (chirped pulse amplification) laser system as a pumping driver. The pumping laser is focused with a line shape and is irradiated on solid metal targets (Ti, Ag and Sn). The x-ray lasers were obtained at wavelengths of 32.6 nm (Ne-like Ti), 13.9 nm (Ni-like Ag) and 11.9 nm (Ni-like Sn). Further experiments will be planned using seeding light amplification for generating highly coherent x-ray lasers.

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