Development and characterization of a pulse generator which enables active control of a laser-assisted pulsed plasma thruster were conducted. In addition, thrust performance of the thruster was measured. As results of operational tests of the pulse generator, it was confirmed that timings of a laser pulse and a discharge pulse were actively controlled with an arbitrary delays. Moreover, typical values of a peak discharge voltage and a period were 15 kV and 160 ns, respectively. In addition, it was shown that the measured impulse bits were proportional to charge energies to capacitors.

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A substantial improvement of propellant utilization efficiency can be achieved by reducing the diameters of accelerator grid apertures by ion machining, in which the accelerator grid hole geometries were defined self-consistently. In this paper, a fast ion machining calculation method is proposed, which can be used to design a high performance ion thruster accelerator grid with small computation time. Calculation results using this method were compared with the ion machined accelerator grid apertures of the μ20 ion thruster obtained by experiments and ordinary time-marching simulations using the JIEDI tool. The comparisons showed that this method is very fast and successfully gave the accelerator grid hole geometries that provide higher propellant utilization efficiency than the conventional method. This method was also applied to the design of the grid hole geometries of an on/off ion thruster. The ion-machined accel grid successfully reduces ion leak during the extraction-off period than the ordinary straight hole grid.

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This paper describes water-propellant magnetoplasma dynamic (MPD) thruster. High power electric propulsion systems attract attention as a next-generation mass transport system. Today, allelectric satellites, which have no chemical thruster, were launched and will be used as communication satellites. MPD thrusters are one of the most promising electric propulsion devices because of relatively simple structure, high specific impulse and thrust to power ratio. Conventionally, hydrogen, ammonia, and hydrazine propellants were tested for MPD thruster. Hydrogen propellant produced the highest specific impulse though it requires cryogenic cooling and high-pressure tanks for the storage. Ammonia and hydrazine are storable propellant but are deleterious and toxic substances, respectively. Hence, the authors propose to use water as a propellant for MPD thrusters. A coaxial-electrode type prototype was tested to show that 100-kW class waterpropellant MPD produces arc discharge and investigate the correlation between discharge current and voltage.

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Electrical characteristics and the electron density of the argon inductively coupled plasma (ICP) driven by high voltage pulse burst with 150 kHz-band at several pressures was evaluated based on a mutual induction model. The electrical parameters on an equivalent circuit of the mutual induction model of ICP were obtained from waveforms of coil current and voltage. The pressure was varied from 5 to 14 Pa. The frequency and the width of burst pulse voltage were 157 kHz and 200 μs, respectively, and its repetition rate was 1 Hz. When the input electric power into the ICP ranged from 2.7 to 11.9 kW, the coupling coefficient between the coil and plasma and the plasma impedance ranged from 0.66 to 0.70 and from 0.022 to 0.035 Ω, respectively. Assuming that the uniform cylindrical plasma was maintained at the burst pulse period, the electron density were estimated as 1019 m-3 with the effective electric field of the ranges from 75 to 132 V/m.

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A capacitor charging power supply for pulsed power generators has been developed with a forward-type single chopper geometry. GaN-HEMT (TPH3206) and SiC-MOSFET (SCT2120AF) as a next generation power semiconductor switch have been compared for high speed switching device of single chopper. In addition, cobalt-based amorphous (FS32) and nanocrystalline soft magnetic material (FT-3M) have been compared as a toroidal core for pulsed transformer. In this work, capacitor charging power supply has been constructed on circuit simulator and universal board. In both simulation and experiment, TPH3206 has shorter capacitor charging time up to 1000 V than SCT2120AF. In addition, FT-3M was able to charge capacitor up to 1000 V faster than FS32.

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Effect of gene expression in plant seeds irradiated by low-pressure oxygen plasma has been investigated using microarray analysis and quantification of DNA methylation. The active oxygen species generated in oxygen plasma acted plant seeds, and increased the DNA methylation level of plant seeds determined using DNA methylation quantification method. This indicated that gene expression in plant seeds induced by active oxygen species was owing to epigenetic variation of DNA methylation.

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