As a new approach for vertical compact toroid (CT) injection, we have proposed a magnetically control method of CT transport for the purpose of injecting a CT vertically in any radial direction by a single CT injector. We have successfully demonstrated switching of the CT traveling direction in a forked drift tube by the application of an external magnetic field.

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Techniques for the neutral transport simulation using a Monte-Carlo code are briefly reviewed by explaining the examples of the simulation with the DEGAS Monte-Carlo code. Tandem mirror plasma produced in GAMMA 10 is employed as a target plasma for the simulation. An axisymmetric simulation using the ver.35 code is applied for the central-region and a three-dimensional simulation in non-axisymmetric anchor region is performed with the ver.63 code. In this review brief introduction of both versions, newly introduced processes and mesh models designed for axisymmetric and non-axisymmetric structures in the GAMMA 10 are described.

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We review methods of generating microplasamas and the issues involved in generating them efficiently such as developing miniature discharge circuits and active-functional electrodes. Because the size of plasmas is extremely small, new experimental schemes not common in conventional plasma apparatuses will be applicable. The microplasma discharges are established with solid, liquid, and gaseous matter. The pulsed power system is one of the effective ways to power the discharges, given that the electrical energy has to fill small volumes over relatively short time in order to avoid energy and particle losses. Nano-sized-structure and active-functional electrodes are developed to establish control of electrons, which is essential to obtain uniform and stable discharges.

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Properties of microplasmas can be characterized not only by their small sizes from mm to μm but also by their relatively high plasma densities which range over 10¹³ cm^-3 in collision dominant atmospheres. These features are due to the high operating pressure generally used, in accordance with Paschen’s law. In addition, the plasma-wall interaction becomes important, given that the charges accumulated on the surface can strongly affect the discharge and plasma behaviors. Diagnostics and simulations should aim to clarify those specific properties of microplasmas. Although there are many difficulties inherent in measurements in such small spaces, several methods have been developed by using optical absorption, fluorescence, and scattering techniques by using various lasers as the light sources. For the simulation, in most cases fluid, particle and Vlasov models can be applied to microplasmas operating at higher pressure. The computer simulations are performed to investigate and produced microplasmas. In this chapter, an overview of our studies on the diagnostics and simulations, mentioned above, will be introduced.

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In addition to generation and diagnostics of microplasma, application studies of microplasmas have been performed intensively. Based on the unique characteristics of microplasmas, such as an extraordinary locality and high density, developments of various new application technologies are in progress. Those include, e.g., novel materials processing, biomaterials treatment, chemical analysis, light sources of ultra-short wavelengths, three-dimensional micromachining tools and other functional plasma devices. In this chapter, an overview of our studies mentioned above on the applications will be introduced.

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Neutron diagnostic is one of the powerful tools for the fast ion study in the DD and DT burning plasmas. Neutron production processes in burning plasmas and the neutron diagnostic techniques are briefly reviewed. The transport analysis of the neutron yield in the NB heated JT-60 plasma provides the fast ion contribution in the neutron production process. The fast ion slowing down process has been studied by the NB blip experiments at JT-60. Triton burn-up measurement has been carried out with the 14-MeV neutron measurement in the DD plasma, which shows that the behavior of 3.5-MeV tritons is almost classical. Neutron emission during the TAE mode driven by 400-keV negative-ion-based NB has been investigated at JT-60. The knock-on α spectroscopy is tried in the DT campaign of JET by the magnetic proton recoil spectrometer.

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In order to improve the measurement performance of incoherent Thomson scattering diagnostics, a high performance phase conjugate mirror based on stimulated Brillouin scattering (SBS-PCM) is applied to a Thomson scattering system for the first time in the JT-60U tokamak. We have demonstrated that a SBS-PCM which uses heavy-fluorocarbon liquid showed a high reflectivity of 95% at a high input-power of 145 W. Using the SBS-PCM, two newly developed methods were employed to increase the amount of scattered light. In the first method, we first developed a new optical design to provide a double-pass scattering scheme with the SBS-PCM. In this new optical design, a laser beam passing through the plasma is reflected by the SBS-PCM, and the reflected beam is returned via the same path by means of the phase conjugate effect, and is then passed through the plasma again, in order to increase the scattered light. A double-pass Thomson scattering scheme using the SBS-PCM was demonstrated in JT-60U ohmic plasma, resulting in an increase of the scattered light by a factor of 1.6, and the reduction of relative error by 2/3 for electron temperature measurement in contrast to single-pass scattering. A multi-pass Thomson scattering scheme is also proposed based on the results of double-pass scattering. It is estimated that multi-pass scattering allows the generation of several times the amount of scattered light, and the reduction of the relative error for electron temperature measurement by 37% in contrast to single-pass scattering. Regarding the second method, a high average-power of YAG laser system was developed by applying the SBS-PCM to a existent diagnostic laser. As a result, the average-power was increased by over 8 times in contrast to the average power of the original system, achieving up to 368 W (7.4 J × 50 Hz).

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The plasma confinement properties of Heliotron J plasmas and the toroidal current are investigated. A plasma energy of 2.5 kJ has been achieved by 70 GHz0.35 MW electron cyclotron heating (ECH). The energy confinement time is within the expected values as determined by the stellarator scaling law. In the high density region, however, better confinement plasmas are observed. The transition phenomena characterized by Hα signal drop are sometimes observed in such a region. The toroidal current generally affects plasma confinement since it generates a poloidal magnetic field. From this point of view, toroidal current control is studied in terms of field-component variation and electron cyclotron current drive. The zero current condition is found in the inner vertical field scan. Current control using the electron cyclotron wave is also demonstrated.

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High purity V-4Cr-4Ti alloy (NIFS-HEAT2), fabricated by National Institute for Fusion Science (NIFS), was used for this study. The samples were annealed at 1,273K for 2 hours and bead-on-plate welds were performed using high purity argon gas. The measured oxygen concentration of the sample before welding, and weld metal are 139 and 158 wt ppm, respectively. A 2.4 MeV copper ion irradiation was carried out with the tandem accelerator at Kyushu University. The TEM (Transmission Electron Microscope) samples were sliced from the welded materials and irradiated at 573 K and 873 K up to the dose of 12 dpa. The microstructure before irradiation showed that relatively large Ti(C,O,N) precipitates which were commonly observed in NIFS-HEAT2 disappeared in the center of weld metal. After the ion irradiation at 873K, fine titanium oxides with {100} habit plane were detected at the dose of 0.75 dpa. Lower number density of the oxides was observed in the base metal after the same irradiation conditions. This means that the contribution of oxygen atoms, which dissolved from the large precipitates during the laser welding, is essential to the microstructural evolution of welded V-4Cr-4Ti alloys.

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