Study of DC-biased microwave discharge by changing anode structure in a 10 cm diameter ion thruster

Abstract Research has been carried out on a hybrid discharge ion thruster, aiming to combine the advantages of Direct Current (DC) discharge ion thrusters (known for their high thrust density and high power supply efficiency) with microwave discharge ion thrusters (which do not require a hollow cathode and are capable of efficient ionization at low pressures). Comparative experiments with different anode structures and single-probe diagnostics revealed that applying a DC bias voltage created a new ionization zone based on microwave discharge. This DC bias increased the sheath potential of the screen grid and led to an elevation in electron temperature and plasma density. It is speculated that the reduced loss of high-energy electrons generated by microwave discharge at the screen grid is the primary reason for the enhanced discharge. By adding a DC bias of approximately 50 V to the microwave discharge, the screen grid current was doubled without a significant increase in discharge power consumption. Under appropriate bias voltages that consider minimizing ion sputtering, DC bias holds promise as a design approach to increase the extracted beam current in microwave ion thrusters.