Investigation of materials for radio frequency antenna plasma facing components

The interaction of radio frequency (RF) sheaths with plasma facing antenna materials is being studied to determine their erosion characteristics. Experiments are being conducted on the Radio Frequency Plasma Interaction Experiment (RF PIE), which consists of an electron cyclotron resonance plasma source (2.45 GHz, 5 kW) with a biased and heated RF electrode. Helium and/or deuterium plasmas (density of ~1e18/m³, electron temperature of 4-5 eV) are being used to explore both DC and RF sheath formation on materials, with average bias voltages up to 500 V. Optical emission from the sputtered material is being used to infer sputtering coefficients as a function of bias conditions. When compared to DC sheaths, it has been shown that the sputtering of tungsten due to RF sheaths has the effect of enhancing the erosion. RF biasing causes a broadening of the ion energy distribution function, as calculated using the hPIC2 code, and this broadening causes enhanced erosion due to the high energy tail of the distribution. Optical emission lines from other candidate materials, including SiC and TiB₂, are being identified, with the goal of predicting the erosion of these materials under similar conditions. Experimental details will be presented.