Speaker
Description
See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1014.pdf
The overall goal of the IShTAR (Ion Cyclotron Sheath Test ARrangement) project is studying antenna near-fields in the presence of a plasma and magnetic field to assess theoretical predictions on RF sheaths and to guide theoretical modelling [1]. For antenna studies it is favourable to operate at tokamak edge-like conditions for density and temperature. Plasma characterisation has been done in a systematic way in order to obtain reproducible density profiles in front of the ICRF antenna. An extensive exploration of the discharge parameters (such as the neutral gas pressure, the gas type, the helicon antenna power and the magnetic field topology) was performed. Resulting density profiles will be presented. They have been obtained by an array of langmuir probes. The profiles have been documented in a database, which can be directly used for future operations. Furthermore, progress will be reported on electric (E) field measurements using helium spectroscopy. A new gas injection system has been implemented, which allows for a local gas puff of helium in the vicinity of the ICRF antenna. The goal is to increase the emission intensity of the spectral lines at the location of the sheath. In that way argon can be used as main gas, which creates plasmas in IShTAR with densities that are 10 times than for pure helium. The system is operational and first results will be presented. Also, a fibre bundle has recently been installed to complement the single fibre observation point, which was reported in [2]. The array focuses 7 fibres onto a 1 cm spot at the edge of the ICRF antenna. The fibres are stacked on top of each other at the entrance slit of a high-resolution spectrometer. For high E-fields (above 1 kV) Stark effects can be observed on the helium spectra (typically He I at 474.1 nm is selected). The fibre array will give information on the evolution of the electric field inside the sheath.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The work received support from the Research Foundation Flanders (G0B3115N).
[1] K. Crombé et al., "IShTAR: a helicon plasma source to characterize the interactions between ICRF and plasma", 26th IAEA Fusion Energy Conference (2016), EXP6_48.
[2] A. Kostic et al., "Development of a Spectroscopic Diagnostic Tool for Electric Field Measurements in IShTAR (Ion Cyclotron Sheath Test ARrangement)", Review of Scientific Instruments (2018) 89 (10), 10D115.
