Ion extraction experiment for electron cyclotron resonance ion source with different magnetic topology

Abstract

Electron cyclotron resonance ion source (ECRIS) for space propulsion requires to be compact and efficient. In this work, ECRIS, which generates magnetic field through permanent magnets, is compact and heats electrons by microwave in magnetic field to induce ionization collision and produce plasma. In ECRIS, magnetic field is crucial in gas discharge, plasma confinement and transport. Due to the complex interaction among the processes, including plasma generation, wave transmission and ion extraction, the effects of magnetic field on the performance of ECRIS are complex. In this paper, the effects of magnetic field topology on the performance of the ECRIS are studied experimentally. Argon is discharged by microwaves in four types of ion sources, different in the magnet positions and the ion beam extracted. The gas flow rate varies from 30 to 210 g/s, the microwave power from 10 to 20 W and the extracting voltage form 500 to 1500 V. The properties of the ion sources are analyzed by comparing their extracted ion beams, propellant utilization efficiency, discharge loss and stability. Results show that the maximum ion beam, the highest gas utilization efficiency and the minimum discharge loss are respectively 160 mA, 60%, and 120 WA-1. Each ion source presents more than one mode, determined by the microwave power and the gas flow rate, and affected by the extracting voltage. The microwave power and the gas flow rate at which the ion source mode changes relative to the position of the magnets. Finally, the influences of magnetic topology on the performance of the ion source are summarized and analyzed. It is concluded that inside this kind of ECRIS, the magnetic field featured by a wide electron cyclotron resonance (ECR) zone, and the narrow gap between the ECR zone and the screen grid will increase the extracted ion beam at the same level of the input power and the gas supply. But it is difficult to achieve high gas utilization efficiency in the ion source with such a structure. By keeping the ECR zone close to the power entrance, the gas inlet will significantly decrease the threshold for the power and gas consumption to sustain the high current mode. But the discharge loss in the ion source of such a structure is huge. Elaborate considerations should be taken to balance the magnitude of the extracted ion beam and the efficiency. These results may improve the understanding of the working process of this type of ECRIS and help the design processes.