Collective Thomson scattering (CTS) is a promising candidate for direct measurement of the velocity distribution function of ions in fusion devices. The relevant frequency for a CTS probing beam source is in the millimeter- to submillimeter-wave range. The scattering volume of CTS is an important parameter for determining the intensity of the scattered power and the spatial resolution of the measurement. The conventional method of estimating the scattering volume is to simply calculate the geometrical volume of the probing and receiving beams. This calculation is valid only when the beams are diffraction free. The effective scattering volume is defined and applied to a CTS system using strongly focused beams and its validity is examined experimentally.

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Ion cyclotron range of frequencies (ICRF) heating antennas in LHD are numerically simulated and analyzed by HFSS^TM finite-element electromagnetic wave field calculation code. The model includes an accurate vacuum chamber wall of LHD and ICRF antenna structure and a simple model of plasma in a helical configuration. Antenna coupling with plasma is simulated by an artificial freshwater volume with enhanced high permittivity of ε = 500-2000. RF current distribution and electromagnetic field distribution on and near the ICRF antenna are analyzed and well elucidated through a comparison with the experimental results. The frequency dependence of experimental loading resistance can be simulated by the calculation, and the RF dissipation on the antenna structure is studied and compared with experimental results. The local high heat load around gaps between the carbon side protectors is well explained, and the effect of gap distance is studied. Comparison with the experimental results reveals that the ICRF heating in the LHD, including the antenna and helical plasma, is well simulated by commercial HFSS^TM code analysis. It will also be useful for future improvements in ICRF antenna design in helical devices.

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A high-power-density ion beam system with high-repetition pulses was successfully developed. In the ITER (International Thermonuclear Experimental Reactor), it is anticipated that an intermittent thermal flux, due to the edge localized mode (ELM), to the plasma facing materials causes severe damage of the mechanical properties. Therefore, it is very important to study the effect of ELM phenomena. We already developed an ion beam system with a power density as high as ∼1 GW/m² around the focal point of the beam. In order to imitate the intermittent high-power-density pulsed flux, we modified the beam operation method and part of the acceleration power supply. A pulsed helium ion beam with the beam width of 2 ms and 4 ms intervals between pulses was successfully extracted. In this case, beam energy, current and power were ∼22 keV, ∼40 A, and ∼0.88 MW, respectively. This high-repetition pulsed helium ion beam with high power density (∼300 MW/m² ) was irradiated to a tungsten material. It was found that this repetitive short-pulse irradiation caused less surface damage compared with long-pulse irradiation, even when the total amount of irradiation fluence (1.5× 10²² particles/m²) was the same for each condition. This would provide important data for the design of ITER diverter.

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To develop a hydrogen pair-ion plasma source comprising only hydrogen atomic pair ions, i.e., H⁺ and H⁻ ions, the efficient production of pair ions is required. When discharged hydrogen plasma is used to irradiate a Ni catalyst, pair ions are produced on the catalyst surface. Hydrogen chemisorption on the catalyst and the electronegativity of the catalyst material are found to affect pair-ion production.

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Thermal display, which is a type of haptic display, is effective in providing intuitive information of temperature. However, in many studies, the user has assumed a sitting position during the use of these devices. In contrast, the user generally watches 3D objects while standing and walking around in large-scale virtual reality system, In addition, in scientific visualization, the response time is very important for observing physical phenomena, especially for dynamic numerical simulation. One solution is to provide two types of thermal information: information about the rate of thermal change and information about the actual temperature. We propose a thermal display with two Peltier elements which can show above two pairs of information and the result (for example energy and temperature, as thermal information) of numerical simulation. Finally, we represent an example of visualizing and haptizing the result of molecular dynamics simulation.

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The boundary node method has been reformulated without using any integration cells and its performance has been investigated by comparing with the dual reciprocal boundary element method (DRM). The results of computations show that the accuracy of the proposed method is superior to that of the DRM regardless of the number of a boundary node, a boundary condition and a boundary shape. In addition, when the number of boundary nodes exceeds a certain limit, the calculation speed of the proposed method becomes almost equal to that of the DRM.

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We introduce new software for analysis of time-varying simulation data and new approach for contribution of simulation to experiment by virtual reality (VR) technology. In the new software, the objects of time-varying field are visualized in VR space and the particle trajectories in the time-varying electromagnetic field are also traced. In the new approach, both simulation results and experimental device data are simultaneously visualized in VR space. These developments enhance the study of the phenomena in plasma physics and fusion plasmas.

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The optical properties of a gold nanorod were investigated by Imura et al. [J. Chem. Phys. 122, 154701 (2005)] using an apertured-type scanning near-field optical microscope (SNOM). The observed transmission image showed an oscillating pattern along the long axis of the nanorod. We obtain the image using the finite-difference time-domain (FDTD) method. Our model includes a nanorod on a glass substrate, a SNOM, and current as a light source. We develop a simple method for including the Drude-Lorentz dispersion relation of Vial et al. [Phys. Rev. B 71, 085416 (2005)] for gold in the FDTD. The oscillating pattern is explained by the total current in the nanorod, tip of the SNOM, and light source.

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A three-dimensional boundary-node method without any integration cells has been formulated. In the proposed method, an implicit surface is assumed as a surface boundary, and the 3D local coordinates are used to evaluate surface integrals. Numerical experiments illustrate that although the computational costs of the proposed method are larger than those of the boundary element method (BEM), the proposed method enables the evaluation of surface integrals without any integration cells. In addition, the accuracy of the proposed method is almost the same as that of the BEM for the Laplace problem.

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A high-performance method has been proposed for calculating the shielding current density in a high-temperature superconducting thin film. After spatially discretized, the initial-boundary-value problem of the shielding current density is reduced to a system of first-order ordinary differential equations that has a strong nonlinearity. However, the system cannot be always solved by means of the Runge-Kutta method even when an adaptive step-size control algorithm is incorporated to the method. In order to suppress an overflow in the algorithm, the following method is proposed: the J-E constitutive relation is modified so that its solution may satisfy the original constitutive relation. A numerical code for analyzing the shielding current density has been developed on the basis of the proposed method and the inductive method has been investigated by use of the code.

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The inductive method and the permanent magnet method for measuring the critical current density in a high-temperature superconducting (HTS) thin film have been investigated numerically. For this purpose, a numerical code has been developed for analyzing the time evolution of the shielding current density in a HTS sample. The results of computations show that, in the inductive method, the critical current density near the film edge cannot be accurately evaluated. On the other hand, it is found that, in the permanent magnet method, even if the magnet is placed near the film edge, the maximum repulsive force is roughly proportional to the critical current density. This means that the critical current density near the film edge can be estimated from the resulting proportionality constants.

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Micelle formation in an amphiphilic solution is investigated by a molecular dynamics simulation of coarse-grained semiflexible amphiphilic molecules with explicit solvent molecules. Our simulations show that the micellar shape changes from a cylinder to a disc as the intensity of the molecular rigidity increases. We find that the radius of gyration of the cylindrical micelle is larger than that of the disc-shaped micelle for small molecular rigidity, although the radius of gyration is almost steady even during the transition between a cylinder and a disc for large molecular rigidity. This indicates that a cylindrical micelle formed at small molecular rigidity is more anisotropic than the one obtained at large molecular rigidity. We also ascertained that a cylindrical micelle and a disc-shaped micelle coexist dynamically over a certain molecular rigidity range.

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The Variable Preconditioned GCR (VPGCR) with mixed precision on Graphics Processing Unit (GPU) using CUDA is numerically investigated. The convergence theorem of VPGCR is guaranteed that the residual equation can be solved in the range of single precision, which means that VPGCR is applicable method to elicit the high performance of GPU. The results of computations show that VPGCR with mixed precision demonstrated significant achievement than that with double precision operation. Especially, the hybrid VPGCR on GPU is 10.10 times faster than that of CPU, and the standard VPGCR on GPU is 10.36 times faster than that of CPU.

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We introduce an adhesive powder model based on the discrete element method (DEM). By using this model, we investigate how fragile substances consisting of a lot of adhesive powders, powder materials, are fractured. In the powder material, the powders have a weak attraction and are stuck to each other by adhesion. Thus, the powder materials are easily broken by the external force. We investigate the crack morphology of the fractured powder materials by changing two parameters expressing the strength of the adhesive force χ and width of the powder size distribution Δ. The fracture pattern is changed from cracking to crumbling as Δ increases for every χ value. Interestingly, we find that this change seems to start at a particular point of Δ from observations of the fractal dimension of the cracks D_f versus Δ. This result may suggest that the morphological change of the cracks may be related with a transition in the granular systems such as the glass transition.

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Plasma technologies using an argon plasma coagulator have been used in endoscopic therapy to induce blood coagulation and ablate residual tumors. However, present devices have a risk of perforating the stomach wall during endoscopic submucosal dissection. Therefore, to reduce this risk, irradiation is performed for a limited time, which leads to incomplete cessation of bleeding and recurrence of residual tumors. Therefore, a device with greater controllability and safety is strongly desired for clinical applications. In this study, we have evaluated the irradiation efficiency of an atmospheric-pressure plasma jet based on a dielectric barrier discharge to control bleeding. Bleeding from a mouse femoral artery was induced, and then plasma was irradiated onto the bleeding area. Prompt coagulation in the disrupted blood vessel was observed, and there was no histological evidence of either burns or tissue necrosis caused by the plasma jet. These results suggest that postoperative scarring and adhesion may be prevented using the proposed plasma generator because of the reduced tissue damage.

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This article summarizes advanced physics in plasma and fusion research, which was covered by the 19th International Toki Conference (ITC). Summary is made from the viewpoint of progress of physics of nonequilibrium properties of plasmas, putting an emphasis upon the theme ‘Knowledge must be developed into understanding'. The aspects of advanced physics in this ITC was assessed in the issues: (i) advance in knowledge of confinement, (ii) multi-scale turbulent structure formation, (iii) transport processes, continued (nonlocal transport, statistical theory), (iv) advanced diagnostics, (v) reconnection, magnetic islands and MHD activities, (vi) plasma atomic molecular physics, (vii) integrated modelling, (viii) problem definitions for reactor studies, (ix) solar, space and astrophysical plasmas, (x) nano-bio plasmas, and (xi) further extensions. This report summarizes achievements in plasma physics with the perspective of 20 years of National Institute of Fusion Science after its inauguration.

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