The characteristics of the helicon plasma injection into the IEC were explored. The first such analysis was a COMSOL simulation to determine the voltage as a function of position in the helicon dielectric tube when the IEC cathode is biased to several kilovolts. This COMSOL simulation contained no plasma and a ~20 V drop in the helicon dielectric tube was determined. To build upon this COMSOL model which contained no plasma, calculations of the theoretical ion flow rates were performed. These calculations used the measured ion current to determine the ionization fraction. Using the ionization fraction as an input into the zero dimensional model an electron temperature was obtained. With the electron temperature, collision and sheath/presheath properties can be determined. Finally entering the collision and presheath/sheath properties into a diffusion equation yields an ion flow rate that was on the same order of magnitude as the measured ion flow rate (~1016 s-1). The similarity between the theoretical calculations with the measured values verified some of the assumptions made in the theoretical calculations. Such assumptions include approximating the voltage drop in the presheath, which includes the length of the helicon dielectric tube, as on the order of the electron temperature ~2.85 eV. This assumption was based on the literature and showed that effects such as Debye shielding play a large role in screening out large cathode biases. So increasing the cathode grid bias does not necessary increase the ion flow rate significantly.
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Analysis of energy balance in a helicon coupled to an inertial electrostatic confinement device
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