Paper PS-ThP17
Stabilization of Ion-beam in Hall-type Plasma Processing Device

Thursday, October 18, 2007, 5:30 pm, Room 4C

Hall-type plasma processing device, whose ionization/acceleration mechanisms are extremely same as magnetron, has great expectations as ion beam source for nano/micro processing. Plasma magneto-hydrodynamic(MHD) instability, however, causes at high-voltage mode operation of DC regime. In particular, large-amplitude instability in the tens of kHz has been a serious problem that should be solved to improve the operational stability and the device system durability. So we propose a hall-type plasma processing device with new design concepts that is capable of solving simultaneously the instability and the accelerator core overheating. The technologies for this concept are as follows: 1) To increase neutral species velocity-inlet in acceleration channel by preheating propellant at its conduit line inside accelerator system could bring about the lower amplitude. 2) This method of preheating propellant through circularly propellant conduit line inside propulsion system cools the device system, and produces the higher thrust and specific impulse with hardly changing thrust efficiency at the same time. 3) Furthermore, to select Boron-Nitride and Al2O3 as wall material of ionization- and acceleration-zone in acceleration channel respectively having different secondary-electron emission-coefficient could achieve the higher-efficiency and -durability. The hall-type beam accelerator designed using these technologies, which have high convergence and stabilization of high-power beam at a low-price, becomes a enhanced ion beam source. Verification of these reduction technologies is conducted through numerical analysisand experimental data: The dependencies of both performances (ion generation-/acceleration- efficiency/ energy-efficiency/propulsion-utilization efficiency) and instability amplitude/frequency on various parameters (discharge voltage/neutral species temperature/magnetic field profile) are estimated using unsteady numerical analysis and experimental data. Besides in order to clarify the physical mechanism of the technologies a new physical parameter ‘equilibrium length of ionization-zone’ is introduced. Also the spatiotemporal variations of plasma properties and electromagnetic field for the optimum operation are examined in the acceleration channel at the peculiar times in instability-cycle.

This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists (A).