Nano-composite silicon powders have been produced at a maximum process throughput of 6 g/min by plasma spraying with metallurgical grade silicon powder as raw material. The obtained powders are found to be fundamentally composed of crystalline silicon particles of 20-40 nm in diameter, and are coated with an $5-nm-thick amorphous carbonous layer when methane gas is additionally introduced during plasma spraying. The performance of half-cell batteries containing the powders as negative electrodes has shown that the capacity decay observed for the raw Si coarse particles is significantly improved by plasma treatment. The carbonous coating potentially contributes to an improvement in capacity retention, although coexisting SiC particles that inevitably form during high-temperature processing reduce the overall capacity. V C 2014 AIP Publishing LLC.

AC Ohmic coil operation experiments with frequencies up to 10 kHz were performed on the TST-2 spherical tokamak device, and the pre-ionization process was studied in detail. The minimum loop voltage for pre-ionization was 0.4 V, which corresponds to 0.5 V m −1 at the inboard limiter. Dependences of growth rate and saturation level of the process on various parameters were obtained, and they are compared with a time-dependent 0-dimensional model based on Townsend avalanche and loss along field lines. Most of the dependences are reproduced qualitatively by the model, and quantitative differences are within a factor of several. However, the external vertical field dependence of the appearance time, which is defined as the time to observe a plasma, and the isotope effect cannot be reproduced by the model. An ambipolar diffusion state which is predicted theoretically but mitigated experimentally is discussed. It was found that secondary electron emission at the limiter surfaces is a candidate mechanism to mitigate the state.

In the TST-2 spherical tokamak device, we carried out a fully non-inductive current startup experiment by Landau damping of the Lower Hybrid Wave (LHW). Capacitively Coupled Combline Antennas (CCCAs) were used for wave injection. The antennas are located on the outboard side and the top side of the vacuum vessel, and by reversing the toroidal magnetic field, it is possible to simulate the case of wave injection from the bottom side. The highest plasma current of 26.7 kA was achieved by top injection with the reversed toroidal magnetic field. According to numerical calculation using ray tracing and Fokker-Planck codes (GENRAY/CQL3D), the downshift of the parallel wavenumber helped the tail of the electron velocity distribution extend to higher energy than the other cases. Additionally, in order to evaluate the directionality of the wavenumber spectrum which is also important for efficient current drive, a finite element solver (COMSOL) was used. In order to avoid deterioration of the wavenumber spectrum, one limiter of the outboard antenna should be moved away toroidally by 70 mm from the current position, and the preferred distance between the antenna and the cutoff density layer is about 2 cm.

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