This Year 2017 is the 25th anniversary of the IAPS (Institute of Applied Plasma Science). Therefore this Issue of the Applied Plasma Science (Journal of the IAPS) is the 25 times issue: Volume 25. Time passed too fast. As it is said to be like a shadow arrow, these 25 years of the IAPS have gone by in a blink of an eye, although there were twists and turns during the progress. I would like to promote in the next five or ten years for the progress of Applied Plasma Science, by challenging new design of the IAPS. Therefore, I would like to ask your cooperation as a member of the IAPS.

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We have designed and manufactured a 100 A class electron emitter for high electric propulsion systems of space crafts. The electron emitter shape and materials were determined by the plasma analysis and the heat analysis. As the result of the operation test, the electron current of 100 A was successfully extracted. The operation reached to the steady-state within 10 sec in any case. In the low flow rate and high discharge current case, the discharge voltage was larger than other cases in order to extract the electron forcibly. In this case, the discharge voltage was fluctuated and a plume spread conically.

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In Hall thrusters, low frequency ionization oscillation is deeply linked to discharge oscillation. It is known that azimuthal non-uniform propellant supply could suppress the discharge oscillation at the expense of thrust efficiency due to increased axial electron current. In this research, we investigated plasma properties’ distributions in the azimuthal dimension which are naturally inherited from non-uniform propellant supply in a Hall thruster discharge channel. It was found that mitigation of locally occurring discharge oscillation was closely linked to the mitigation of total discharge oscillation, and that there is increased electron current by the steady out-of-phase of electron density and plasma potential. Lastly, we found that electron temperature, which is usually considered homogeneous in the azimuthal direction, can be inhomogeneous distribution.

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The objective of this study is to develop a microthruster, utilizing a reaction force of the molecular flow generated through dissociation of molecular bonds of solid polymer targets by irradiation of ultraviolet (uv) photons, namely photo-dissociations. The uv-photons, carrying higher photon energies, are capable enough to directly dissociate the molecular bonds having lower bonding energies than the photon energies. In this study, the uv-photons from light emitting diodes were irradiated to two types of solid polymer targets, nylon6 and polyvinyl chloride (PVC), to compare each mass consumption rates and thrusts caused through the photo-dissociation. The results showed that PVC target generated higher thrusts in lower propellant mass consumption rates than nylon6.

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This paper describes influence of combustion-chamber-pressure change on arcjet plasma source. To yield stable and effective combustion, arcjet plasma is applied to combustion chamber because arcjets readily produce stable high enthalpy flow. However, variation in combustion-chamber pressure sometimes disturbed arc discharge; rise in combustion chamber pressure increased discharge voltage and plenum chamber pressure of arcjet. Hence, the response of arc discharge to pressure variation of combustion chambers would destabilize both combustion and arc discharge. Hence, we evaluated influence of increase in combustion-chamber pressure on discharge voltage, and rate of sustaining arc discharge after increment in combustion chamber pressure. The tests showed that discharge voltage was increased by a factor of 2.5 due to pressure increment of 0.25 MPa at a rise time of 200 ms.

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A discharge phenomenon was investigated to clarify basic property on cavitation bubble plasma in sodium chloride solution. The discharge plasma emission was observed by using charge coupled device camera with a high speed gated image intensifier unit. Generation and annihilation of plasma in the same cavitation bubbles were continuously repeated. The arch-like discharge path was formed on upper parts of the opposite electrodes because of cavitation bubbles produced on the upper parts of the electrodes besides the rotor part., which gradually extended to the direction that the solution flowed through. The maximum height of the arch-like discharge path was 4 mm, meanwhile the voltage of 160 pulses was applied between the electrodes. It was suggested that these phenomena were repeated in the different cavitation bubbles.

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Metal nano-particle supported on titania (MNP/TiO2) photocatalysts are effective to generate hydrogen from an ethanol water mixture. Several chemical and physical methods have been reported for the fabrication of platinum nano-particles (PtNP/TiO2) and gold nano-particles (AuNP/TiO2) supported on titania. In general chemical techniques are more employed for the fabrication of these nanoparticles, but from the cost production point of view physical techniques based on plasma/laser are expected to be more advantageous. Furthermore, in the case of plasma generation in a liquid, for example, where the nanoparticles are fabricated directly into a liquid medium, there is the advantage that nanoparticle aggregation is avoided. Here we report on the development of a photocatalyst based on titania-supported platinum nanoparticles fabricated by cavitation bubble plasma technique and on its application for hydrogen generation.

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In this study, discharge characteristics and plasma (electron and ions) acceleration characteristics of high-peak power short-pulse discharges for a gas-fed short-pulse pulsed plasma thruster were investigated. Changing mass flow rate of Ar propellant fed into the rectangular electrodes, pulse discharge characteristics and plasma acceleration characteristics were examined. As a result, the maximum specific impulse of 8200 s was obtained for a mass flow of 0.1 sccm and repetition rate of 1 kHz.

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