Speaker
Kristel Crombe
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1010.pdf
New Diagnostics Developments on IShTAR
K. Crombé1, 2, A. Kostic1, 3, A. Nikiforov1, R. Ochoukov3,
I. Shesterikov3, M. Usoltceva1, 2, 3, T. Verstrynge1, H. Faugel3,
H. Fünfgelder3, S. Heuraux4, J-M. Noterdaeme1, 3 and the IShTAR team
1
Department of Applied Physics, Ghent University, 9000 Ghent, Belgium
2
LPP-ERM-KMS, TEC partner, 1000 Brussels, Belgium
3
Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany
4
Université de Lorraine, 54506 Vandœuvre-lès-Nancy, France
The diagnostics developed for IShTAR (Ion Cyclotron Sheath Test ARrangement) are
oriented towards measurements of plasma parameters and electric fields in the vicinity of a
Radio Frequency (RF) antenna in order to provide input for sheath modelling codes [1, 2]. In
IShTAR the plasmas are created with a helicon antenna operated at a frequency of 11.76 MHz
and with a power up to 3kW (the maximum power coupled to the plasma is around 2.7 kW).
Recent improvements have been made for the density measurements in the helicon source and
the main vessel. An optimised performance regime was found; by adjusting the magnetic
topology the plasmas density can be increased by a factor 3 to 5, which is beneficial to the
sheath studies. An additional array of RF compensated probes (Langmuir, B-dot…) has been
installed to allow for a better characterization of the plasma parameters at different locations.
The first results of an interferometer, installed to benchmark the electron density estimates of
the Langmuir probes, will be presented.
Two approaches are followed to measure the electric fields in the plasma caused by the RF
antenna sheaths. Passive optical emission spectroscopy monitors Stark effects on spectral
lines with a high-resolution spectrometer [3], provided that the local electric fields are strong
enough to overcome the broadening of the lines. Doppler-free saturation spectroscopy is more
powerful: a laser beam depletes the ground state, eliminates the line broadening effects and
makes smaller electric fields visible. However, the more complicated set-up, with a careful
alignment of laser beams, makes the measurements much more challenging. After a first test
on a glow discharge plasma [4], the design of the optical path and the installation of the laser
at IShTAR have started; the progress will be reported.
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] L. Lu et al., “Modelling of radio frequency sheath and fast wave coupling on the realistic ion cyclotron
resonant antenna surroundings and the outer wall”, Plasma Phys. Control. Fusion, Vol. 60, No. 3, 035003 (2018)
[3] A. Kostic et al.: "Feasibility study of Passive Optical Emission Spectroscopy for the electric field
measurements in IShTAR”, EPJ Web of Conferences 157, 03025 (2017)
[4] K. Crombé et al.: “Helium operation of IShTAR in preparation of E-field measurements”, ECA Vol. 41F, P5-
144 (2017)
