T his paper deals with the dependenc y of performance on repetitive fir i ng frequency for the coaxial type pulsed plasma thruster (PPT). PPTs produce small impulse bits (impulsive thrust) and have simple structure s thank s to the use of solid polytetrafluoroethylene propellant and throttling capabilities with adjusting repetitive firing frequency. Variable thrust using repetitive firing frequency is compatible with digital control and necessitates no variable voltage regulated power supply. However, there have been a few studies on the influence of repetitive firing frequency on performance. Hence, in this study, a 5 J coaxial type PPT was designed to evaluate the dependenc y in the frequency range from 1 to 7 Hz. Thrust measurement showed that higher repetitive firing frequency increased specific impulse, thrust to power ratio, and thruster efficiency but reduced total impulse due to the decreased number of shots until the end of life.

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In this study we investigated the minimum f iber laser power to generate argon las er sustained plasma (LSP), fractional absorption temperature, and length of LSP at various gas pressures and F numbers The minimum laser power was decreased with increase d gas pressure from 0.75 MPa to 1.0 MPa and F number from F 5 to F 10. At 1 0 MPa , with F 10 , the minimum laser power was approximately 460 W. The fractional absorption of the LSP estimated from the transmitted laser power increased from 12% to 40% with gas pressure whereas it has a maxi mum at F12.5 The measured temperatures using emission spectroscopy were 1 1 9 00 to 15,700 K which has little dependency on the variation of F number. The temperature decreased slightly with increased gas pressure The length of LSP increased with gas pressure . At 0.75 MPa and 0.8 MPa the length was maximu m at F12.5.

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In this study, an investigation was conducted for an impact of hollow anode geometries on discharge and thrust characteristics of miniature low power magnetic layer Hall thrusters with Xe propellant . Two types of the hollow anodes with different volumes were examined. As results, it was shown that a thruster with smaller volume of the hollow anode showed tendencies of larger discharge currents up to nearly 30%. M oreover, the thruster with smaller hollow anode showed smaller thrusts (down to about 30%), and smaller anode efficiency (down to about a half).

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Metal ions were generated by sputtering metal targets using a short-pulse-operated high-power impulse magnetron sputtering (HiPIMS) technology. The pulse duration was 25 μs with a maximum source voltage of -2600 V, which efficiently facilitated ionization of the sputtered metal species. Six-inches of titanium (Ti), aluminum (Al), copper (Cu), carbon (C) disks were used as the target materials. Argon was used as sputtering gas with gas pressure from 0.3 to 4.0 Pa. The applied voltage of -2600 V was used to generate magnetron plasma with current of 100 A. The results showed that the metal ions were produced with order of 1018 m-3 in ion density. The ion density increased with decreasing gas pressure and increasing applied voltage. The sputtered metal ion density depended on target material properties such as sputter yield and ionization rate.

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