A 28 GHz 200 kW generation and launching system for ECH/EBW on Proto-MPEX at ORNL

Oak Ridge National Laboratory is developing advanced material-plasma exposure capabilities to test plasma-facing materials for fusion reactors in a realistic edge plasma environment¹. A novel RF heating system is being developed for the Prototype Material-Plasma Exposure Exposure eXperiment (Proto-MPEX). Both ion and electron heating with RF power of magnetically confined linear plasma will be utilized. Microwave power generated by a 200 kW cw 28 GHz gyrotron is used for electron cyclotron heating and RF power at 7-13 MHZ provides plasma formation with helicon waves and ion cyclotron heating. The gyrotron and associated HVDC power supply are from an earlier experiment and have been setup with a new waveguide system and launcher. A TE02 to TE01 to HE11 mode converter system launches power from the gyrotron into 15 m long 88.9 mm corrugated waveguide with 2 miter bends and a mirror launcher in a central plasma chamber on Proto-MPEX. The power is beamed toward a resonance zone at the center of the plasma. At higher density above cutoff at 28 GHz (9×10¹⁸ m³), it is expected that Electron Bernstein mode conversion will take place and the power will be able to propagate to the center and be absorbed. Several plasma diagnostics are being developed to diagnose the plasma conditions at samples and also be useful in optimizing the EBW launch angle and optimization of the density profile. Details of measurements on the waveguide and launching system and initial high power tests will be presented.