DEVELOPMENT OF RADIO-FREQUENCY GENERATOR (RFG) SYSTEM AND PLASMA CHARACTERISTICS INVESTIGATION OF RADIO-FREQUENCY ION THRUSTER

Abstract

In this thesis, the development of a radio frequency (RF) power supply system for the small type of radiofrequency ion thruster and the investigation of plasma impedance inside the discharge chamber are presented. This is a section in the project of developing the entire 50W laboratory model RF ion thruster at the University of Ulsan. The RF ion thrusters inductively coupled plasmas characteristics were investigated by a 0-D discharge chamber analytical model and a 2D axisymmetric numerical simulation. The RF power supply was designed by utilizing class E RF power amplifier topology for high efficiency of power conversion from DC to RF power and impedance matching network for maximum power transfer to plasmas. The RF power amplifier was theoretically analyzed and designed, simulated with a circuit simulation program to design and optimize the performance. The impedance matching network uses the plasma investigation results to approximate the load in the RF ion thruster and design a matched circuit utilizing tunable components. The RF power supply was tested with dummy load and proved to provide stable RF output waveform stably and achieve a high-power conversion efficiency of up to 85%. The simulation of plasmas inside the discharge chamber delivered important information about the characteristics of plasmas that could help to understand and have a better design of RF power supply like plasma density and absorbed power. The RF power system is developed for the small RF ion thruster laboratory model and tested in this model to verify the calculations. This concept could be utilized to develop a larger system with high power and frequency as the efficiency could be increased with better thermal solutions. Plasma analysis using an analytical model and numerical simulation gives a deep insight into the RF ion thruster operating load and assist in the design of the impedance matching network. The tunable matching network concept was digitally controlled which could enhance the matching time, hence increasing the total electrical efficiency of the system. Testing of the RF power system in the vacuum chamber has proved the ability to generate plasma of the power system.