Inertial Electrostatic Confinement (IEC) Device as Plasma Injection Source
In this thesis paper, full experimental and analytical processes of cylindrical IEC plasma injection source and Langmuir probe tests are discussed. The IEC plasma injection source is constructed for DOE project to interact with SiC. Total four versions have been made, and each performance is evaluated. IEC is constructed by two cylindrical grids, which has a positive anode grid and negative cathode grid. It has been demonstrated that higher cathode grid causes higher collision rate between particles, which leads to higher plasma intensity. The radius of plasma depends on anode and cathode grid radius ratio. The higher the ratio, the narrower the plasma beam it produces. In addition, a virtual anode is observed to form within the cathode grid since the plasma beam is never actually in contact with cathode. Further performance tests of 4th version illustrates lower gas pressure and extended anode grids would help plasma have less divergence. At the meanwhile, longer electron tails are formed at lower gas pressure. Single Langmuir probe has been used to obtain IV curve to calculate electron temperature (Tev), electron thermal velocity (ve,th), and plasma density (ne). Those plasma properties have been analyzed for 4th version at 0.4’’ and 0.6’’ away from cathode, respectively. At same probe position, the plasma density increase as cathode voltage increases because of higher collision rate by higher potential fields between electrodes. The result shows the optimum plasma condition is at -1.5 kV and 30 mTorr. At same cathode voltage, the plasma density increases as the probe moves to further distance respect to cathode grid. Nevertheless, the plasma density is around 1016 m-3, which is consistent with other plasma source found in reference papers. The success of controlling plasma injecting only in one direction in a continuous plasma flow demonstrates the potential of this device to operate as a particle (electron or ion) source or small propellant thruster.