Speaker
Ivana Abramovic
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.101.pdf
Collective Thomson Scattering on Wendelstein 7-X
I. Abramovic1,2, D. Moseev2, M. Salewski3, M. Stejner3, A. Pavone2, T. Stange2, F. Leipold3,
S. Nielsen3, J. Svensson2, N. J. Lopes Cardozo1, H. P. Laqua2,
R. C. Wolf2, and W7-X Team
1
Eindhoven University of Technology, Eindhoven, The Netherlands
2
Max-Planck-Institute for Plasma Physics, Greifswald, Germany
3
Technical University of Denmark, Kgs. Lyngby, Denmark
Wendelstein 7-X (W7-X), the World's first so-called "optimized" stellarator, came into
operation in 2016. The experiment is set out to show that the optimization has led to a fusion
device with a confinement at least as good as in its competitor the tokamak. Plasma
diagnostics play a crucial role in this endeavor. Here we present the work on the theory of an
important diagnostic, collective Thomson scattering (CTS), which has been successfully
brought into operation in the last experimental campaign [1]. CTS is a powerful microwave
diagnostic, capable of measuring a number of plasma parameters such as: ion temperature,
plasma composition, drift velocities, and fast ion population. The scattering is collective
when the wavelength of the incident radiation os comparable to the Debye length. The
incident radiation interacts with the fluctuations in the plasma and gives rise to a scattered
wave which is picked up by a heterodyne receiver. What is finally obtained is a spectrum
typically centered at the frequency of the incident wave. Spectra have been obtained from
which the temperature is inferred by the use of a purpose-built forward model (eCTS) [2] and
a Bayesian framework (Minerva) [3] which enables the inference of the parameter values
from the data [4]. The forward model is further developed to enable the measurement of the
radial electric field. We present the novel developments of the theory which were necessary
in order to accommodate the inference of this parameter from the measured spectra. The
theory is extended to non-axisymmetric plasmas and the results of a feasibility study of radial
electric field measurements by CTS are presented.
References
[1] M. Stejner, et al., First collective Thomson scattering results from Wendelstein 7-X, talk EC20, (2018)
[2] I. Abramovic, et al., Forward Modelling of Collective Thomson Scattering for Wendelstein 7-X Plasmas,
submitted to CPC (2017)
[3] J. Svensson, et al., Modelling of JET Diagnostics Using Bayesian Graphical Models, Contributions to
Plasma Physics 51 (2-3) (2011)
[4] I. Abramovic, et al., Collective Thomson scattering data analysis for Wendelstein 7 – X, JINST, (2017)
