Waveguide Assembly and Circular Polarizer for 2450 MHz ECR Ion Sources

Proper coupling of the rf power to the plasma in an electron-cyclotron resonance (ECR) ion source is probably the most important factor in achieving satisfactory performance of overdense plasmas in high-current ECR sources. Poor coupler design can lead to a variety of undesirable effects such as high reflected power, low plasma density, unstable operation, and poor performance. Scientific Solutions has produced an alternative rf waveguide feed assembly for 2450 MHz ECR ion sources currently being used in the community. This new waveguide assembly converts from standard WR-284 waveguide into dielectric-loaded circular waveguide whose transverse dimensions are substantially smaller than the original waveguide. The benefits of this transition assembly are reduced dimensions of the rf window and opening into the plasma chamber, greater freedom in the design of the rf/plasma interface, concentration of the rf energy on the axis of the plasma chamber, a choice of using circularly polarized rf waves, and improved protection of the rf source from reflected rf energy. This assembly is a direct replacement for the WR-284 waveguide and rf window assemblies used in ECR sources and should improve the performance and efficiency of the rf feed system in those sources.