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Kostic, Ana; Crombe, Kristel; Dux, Ralph; Griener, Michael; Usoltceva, Mari; Shesterikov, Ilya; Martin, Elijah H.; Noterdaeme, Jean-Marie (2020): Direct Local Electric Field Measurements in the Sheaths of the ICRF Antenna in IShTAR. In: 23rd Topical Conference on Radiofrequency Power in Plasmas, Vol. 2254, 050002
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An important step in understanding the Radio Frequency sheaths in the vicinity of Ion Cyclotron antennas in magnetically confined fusion plasmas is to benchmark the existing theoretical models against real antenna operation. The data needed is the local DC electric field that develops in the sheaths surrounding the plasma-facing structures of the antenna. In this contribution we present our most recent progress on the development of a spectroscopic diagnostic, which delivers direct and local measurements of the electric field across the sheath. The method uses polarization spectroscopy where the electric fields are optically determined from the Stark shift of the emission spectra of excited helium atoms. The sheath electric fields obtained with this diagnostic scheme are measured in the vicinity of the ICRF antenna in IShTAR, a test facility designed to mimic the tokamak edge plasma parameters and focused on studying the ICRF antenna-plasma interaction.