Microwave rocket is a millimeter-wave beamed energy propulsion (BEP) rocket. The thrust impulse is generated by the millimeter-wave discharge induced in the thruster. The millimeter-wave discharge forms self-organized spatial structures depending on the gas pressure, the millimeterwave frequency, and the local electric field amplitude. In the thruster, the plasma is ignited at the focal point of the parabolic mirror installed at the thruster head. The ionization front of the discharge then propagates in the collimated beam where the electric field amplitude lower than the ionization threshold. We observed the time history of the discharge structure at the focal point of the parabolic mirror and in the collimated beam using a 303 GHz gyrotron as a beam source.

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Influence of applied voltage and frequency on electrostatic elimination by using AC corona Ionizer is investigated. The corona discharge is generated using a needle to ring electrodes with high voltage AC. The compressed air is supplied to an air nozzle to generate the air flows from the electrodes to the ion trapping metal plate. The discharge current increases and the interval of trichel pulse decreases with increasing the frequency of the applied voltage. The electrostatic elimination time decreases with increasing the air velocity. When the air pressure is lower than 13.3 kPa, the electrostatic elimination time increases with increasing the frequency of applied voltage. The bias voltage required to keep ion balance 0 V decrease with increasing the frequency when the frequency is lower than 250 Hz. On the other hands, that increases with increasing the frequency when the frequency is higher than 250 Hz. The air ions generated by the corona discharge are accumulated in the space between the needle and the ring electrodes. The amount of space charge increases with increasing frequency and decreasing air velocity. Therefore, the current into the ion trapping metal plate decreases with increasing the frequency when the air pressure is not sufficiently high.

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Plasma diagnostics of laser ablation plasmas have been widely conducted for utilization of the plasma to industrial and space propulsion applications. In this study, high-repetition-rate (200 kHz) diagnostics of laser ablation plasma were conducted to obtain temporal variations of space potentials, electron temperatures, and electron densities in vacuum environment. For the diagnostics, an emissive probe, on which high-repetition-rate rectangular pulse voltages were applied at 200 kHz, was utilized and installed in an arbitrary position downstream of a Cu target. From the results, it was shown that electron temperatures peaked up to 4.6 eV at 45 us after the induction of laser ablation plasma. In addition, electron densities peaked up to 7.3 × 108 cm^−3 at 20 us. Moreover, from the measurement, it was shown that space potentials of the plasma were about 1.0 V regardless of temporal points within the range of this measurement.

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There are some related issues in the polytetrafluoroethylene (PTFE) coating techniques at room temperature, such as poor adhesion of the coated films. Fluorocarbon (CxFy) films with similar properties to PTFE such as high water repellency and low friction are obtained using the sputtering deposition with a PTFE target. In this paper, the film-substrate adhesion of CxFy films formed by RF unbalanced magnetron sputtering (RF-UBMS) method with a PTFE target is investigated. CxFy films were fabricated on Si substrates under different substrate-bias voltage. Tape-peeling test was performed to evaluate film-substrate adhesion of the films. Results revealed that the application of the substrate-bias voltage slightly reduced the film deposition rate. While CxFy films formed by applying a DC substrate-bias voltage of -50 V showed water repellency close to that of PTFE used as the target with excellent film-substrate adhesion. However, carbon-rich CxFy films were formed under an excessively high substrate-bias voltage of -100 V, exhibiting a decrease in water repellency of the film. This work proves that the application of an appropriate substrate-bias voltage could improve the adhesion between the formed film and the substrate in the sputtering deposition using a PTFE target.

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