Studies on microwave coupling into the electron cyclotron resonance ion source Alice

Abstract

The particular microwave off-axis injection into the electron cyclotron resonance (ECR) ion source Alice, the reflected power and the occasionally observed waveguide arcs, required a careful study both of the waveguide termination and the microwave transmission line. The high-voltage microwave window was redesigned, improving the choke flange and showing the opportunity of treating the teflon insulator to obtain a surface resistivity in the range of 107 Ω. A simple plasma model, unidimensional and based on the Krook model for electron motion, is here considered for the ECR plasma; effects of rapid spatial variation of the external magnetic field are naturally included. Profiles of the waves in the ECR cavity are given, as well as an expression for the impedance of the plasma; no substantial reflections are evidenced for a typical plasma case (ωpl/ω=0.7).