LARGE-DIAMETER PLASMA PROFILE MONITORING-SYSTEM USING FARADAY CUP AND LANGMUIR PROBE ARRAYS

Details of a personal computer-based data acquisition system, which allows monitoring of large-diameter plasma source ion current profiles and Langmuir probe data, using an interchangeable rotatable, Faraday cup array and Langmuir probe array respectively are described. The arrays span the plasma diameter and can be rotated under computer control. Software-selectable monitor modes allow investigation of the angular and temporal dependence of ion current profiles, basic plasma parameters and their associated non-uniformities. Isolated aluminium plates can be fixed to the respective arrays to investigate the intrusive influence of a substrate holder and substrate bias on plasma parameters. Angular dependences is of ion current non-uniformity values of a large-diameter permanent magnet electron cyclotron resonance source are reported to demonstrate the benefits of the system over a single-probe/cup system.