A new semi-empirical technique of 3-D equilibrium reconstruction using the extended virtual magnetic surface coordinate is adopted to determine the plasma boundary surface fitted to experimental data in the Large Helical Device (LHD). The plasma radius is defined by nearly zero plasma pressure, and the core and edge magnetic surfaces are iteratively calculated to fit experimental kinetic pressure.

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Microwave reflectometry is a plasma diagnostic that launches microwaves to a plasma and measures the wave reflected at a cutoff layer in the plasma. It is used mainly for density profile and density fluctuation measurements. Because of its high radial resolution, high sensitivity, and relatively easy implementation, microwave reflectometry has been used in many devices. In this report, highlights of the measurements, as well as the features of reflectometry, are described.

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A PC cluster is no longer for enthusiasts but has become a cost effective computing platform ready to use. The largest problem for users is to modify their existing serial programs to parallel programs using the MPI. This modification is rather easy when the PC cluster is small, and the performance of the program shows high. This report describe basic knowledge and cost of introducing the PC cluster. We measured its performance by a Poisson benchmark test with several variations and report the results, too. We also mention the bottle neck of the performance and its solution.

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This paper introduces an overview of the SCore cluster system software running on the Linux operating system. SCore utilizes PC cluster hardware efficiently and provides its users a high-performance parallel programming environment. This paper also presents brief installation information for the end-users.

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This article provides basic information for making parallel programs with MPI. The author have chosen MPI as a basic programming interface on PC clusters, because the parallel execution model it assumes is very close to clusters. The MPI functions introduced in this article are for sending or receiving messages, broadcasting or reducing data, and starting and ending MPI environments. This article also introduces how to compile and execute MPI programs.

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We have constructed a parallel cluster consisting of Apple Macintosh G4 computers running both Classic Mac OS as well as the Unix-based Mac OS X, and have achieved very good performance on numerically intensive, parallel plasma particle-in-cell simulations. Unlike other Unix-based clusters, no special expertise in operating systems is required to build and run the cluster. This enables us to move parallel computing from the realm of experts to the mainstream of computing.

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The experiences regarding the conctruction of PC clusters in three local laboratories are summarized. The number of CPU's varies from 2 to 32 (1 to 16 PC's). The performance of these clusters scales roughly with the number of CPU's. Using MPI, the merits of dual processing and/or hyper-threading technologies can be applied without any additional programming effort.

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Methods for particle transport analysis in toroidal plasmas are summarized on the basis of particle balance equation. The particle transport model, where the particle flux is expressed as a sum of a diffusion term and a convection term, is introduced. Estimation of the charged particle source due to the ionization of neutral particles is briefly explained for the quantitative analysis of the particle balance based on measurements of neutral particle density and a Monte-Carlo simulation of neutral particle behavior. Several examples for the evaluation of the particle diffusivity and the convection velocity are presented.

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Hydrogen H_β spectrum intensity distributions were measured at three coordinates along the axis of an rf Ar-H₂ plasma torch with a central Ar flow rate of either 0 or 3 l/min. The distributions were inverted to emission coefficient profiles by Abel inversion. Considering that the half widths of the profiles depended only on Stark effect, we calculated electron densities to obtain temperature distributions under the assumption of LTE (local thermodynamic equilibrium). On the other hand, we calculated plasma temperature distribution by the modeling work that assumed laminar flow and LTE state in whole plasma regions. Using the temperatures and chemical species concentrations obtained by the modeling work, we calculated electron densities under the assumption of LTE. Moreover, we observed plasma edges and cold-gas channel generated by the central flow macroscopically by photographing. Using above three method, we tried to elucidate electron density and temperature distributions of our rf Ar-H₂ thermal plasmas comprehensively.

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Radial electric field (E_r) properties in LHD have been investigated based on the neoclassical transport theory and have also been applied to LHD experimental results. The effects of the helicity of the magnetic configuration on the condition required to realize the electron root are examined. The larger helicity makes the threshold temperature lower for the same electron density. A higher threshold temperature is anticipated to be required in the plasma core region based on this fact and also due to the larger density there. This high electron temperature (T_e) has been successfully obtained with a centerfocused ECH. There is a threshold for the ECH power to achieve a steep gradient of T_e, and it seems to be qualitatively consistent with the transition of E_r, at least in the sense that the abrupt increase of T_e occurs after entering the anticipated electron root regime. These experimental results, consistent with those of analysis of the neoclassical ambipolar E_r, indicate that the transition phenomena of E_r in LHD are predominantly governed by neoclassical features.

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