Sub-harmonic ECR heating of microwave plasma in a multicusp magnetic bottle: frequency dependence

The microwave discharge plays an important role in ECR ion sources (ECRIS) as well as in material synthesis and processing. There has been an interest in increasing microwave frequency for enhancing production of the higher charge states in plasmas. This requires energetic electrons in the source and hence it is important to investigate plasma properties like plasma density (ne), electron temperature (Te) and its electron energy distribution function (EEDF). There are studies on effect of input frequency on self-generated plasmas but are limited in megahertz only. However, the input frequency commonly employed in ECRIS lies in GHz range and hence dependence of such frequencies on the resulting plasma properties has remained unexplored. In the present study, detailed investigation of ne, Te and EEDF of microwave plasmas as a function of the driving wave frequency (6 – 11 GHz) is presented