A double-cavity electron cyclotron resonance plasma source

Abstract

Summary form only given, as follows. We have recently developed an electron cyclotron resonance (ECR) plasma source with a double cavity design. The external B-field is generated by permanent magnets placed around the cylindrical plasma chamber to form a multicusp or ring shaped ECR resonant layer. The 2.45 GHz microwave is coupled to the upper cavity by a coaxial probe antenna. The height of the upper cavity can be adjusted to have a single TM/sub 011/ mode in the upper cavity. The upper cavity is coupled to the lower cavity through a 5-cm diameter coupling iris. A flat or conic shape quartz window is placed in the lower cavity to allow microwave transmission to the vacuum plasma region. Conducting extraction grids may be placed at the bottom of the lower cavity. In the lower cavity, the microwave is maintained at TM/sub 012/ mode. In such a design, the change in plasma impedance due to the change in plasma condition has little effect on the impedance of the whole system. Reflected microwave power can be easily tuned to a minimum by slightly adjusting the height of the upper cavity. Even without any tuning, the reflected microwave power can still be at low values at wide operating conditions. With a double cavity design, it is possible to have an easy tuning and high stability ECR plasma source. The plasma properties at various operating conditions were measured by Langmuir probes.