Design of the MPEX Plasma Production and Ion Cyclotron Heating Systems

Steady-state plasma production and ion heating in the MPEX (Material Plasma Exposure eXperiment) are both achieved using RF based systems. High density plasmas are created by a Helicon plasma source coupling power of up to 175 kW at 13.56 MHz through a water-cooled cylindrical vacuum window via an external quarter-turn helical antenna. Ions are heated using fundamental ion cyclotron heating (ICH) in a “magnetic beach” configuration, coupling up to 310 kW at 4-9 MHz through a similar window, with waves coupled by a pair of phased half-turn helical antennas. The designs of the launchers, feed and matching networks, and vacuum windows will be described. The plasma coupling and predicted input impedances for both launchers has been investigated using 3-D COMSOL models that include accurate magnetic field and RF-relevant antenna geometries. For the ICH case, finite electron temperature effects previously seen to be important at MPEX-relevant plasma densities¹ are included. These results have been used together with other data and modeling to investigate power handling of the various components. 

¹P. A. Piotrowicz et al., Phys. Plasmas 26, 033511 (2019).