Plasma Line Emission Measurements for Assessment of Tungsten Sputtering on the Radio Frequency Plasma Interaction Experiment

Filterscopes are being used to measure the line emissions from plasma material interactions of a biased tungsten electrode in the Radio Frequency Plasma Interaction Experiment (RF PIE). A 2.54 cm diam tungsten electrode is exposed to a helium or deuterium-argon plasma generated via electron cyclotron resonance at 2.45 GHz (density 5e17/m³, temp 4-5 eV) and biased with either DC or RF voltages up to 550 V. Ratios of He lines at 667.8 nm, 706.5 nm, and 728.1 nm are being used to determine changes to the electron density and temperature near the electrode due to biasing conditions and are compared with the local parameters measured with a double Langmuir probe. The W I line at 400.9 nm is being measured for comparison with results from a 1-meter Czerny-Turner spectrometer. Filters with various bandwidths are being used to determine their effectiveness at filtering out the emission from nearby helium or argon lines. Multiple viewing chords are being used to determine the axial variation in front of the electrode. Tungsten emission as a function of bias voltage is observed to start near the threshold energy for helium (~100 eV) and increase in a way that is consistent with the expected sputter yield. Experimental details, as well as application of tungsten filterscope techniques for DIII-D and WEST, will be presented.