[Zurück]

B. Vanovac, E. Wolfrum, S. Denk, F. Mink, F. Laggner, G. Birkenmeier, S. Freethy, E. Viezzer, M. Dunne, M. Hoelzl, F. Orain, N. Luhmann Jr., . ASDEX Upgrade Team, -. EUROfusion MST1 Team:
"Effects of strong density fluctuations at the plasma edge on ECEI measurements at ASDEX Upgrade";
Poster: 44th EPS Conference on Plasma Physics, Belfast/United Kingdom; 29.06.2017; in: "Proc. 44th EPS Conference on Plasma Physics, Europhys. Conf. Abstracts", 41F, 4.122 (2017), 979-10-96389-07; S. 1 - 4.

The Electron Cyclotron Emission Imaging (ECEI) diagnostic, with multiple lines
of sight (LOS), where each LOS behaves like a conventional 1D radiometer, measures the electron
temperature and its fluctuations on ms time scales and is specially suitable for 2D or quasi-3D
visualisation of MHD phenomena. Its excellent poloidal resolution enables measurements of the
poloidal velocity of MHD events.
In the case of optically thick plasmas, where optical thickness is proportional to the product of
electron density and the temperature, the intensity of the electron cyclotron radiation equals the
level of the black body emission. However, when measuring at the plasma edge, where the density
and temperatures are relatively low, the electron cyclotron emission no longer equals the black body
radiation and the density contribution cannot be neglected. The ECEI diagnostic has an oblique
observation angle [1] enhancing the Doppler shift of the resonant positions and the deflection of
the beams with the largest incident toroidal and poloidal angles. The measurements of the ECEI
are focused on hot H-mode plasmas where the hot electrons of the Maxwellian tail obey relativistic
mass increase, and so the resonances are shifted towards the higher magnetic field. Taking into
account all these effects the radiation transport equation is solved in order to obtain the radiation
temperatures and correct resonance positions called the warm resonances [2, 3, 4]. For the discharge
studied in this work, the forward model has shown that the presence of the density fluctuations can
influence the radiation temperatures. Therefore the knowledge on both, density and temperature, is
very important for the interpretation of the ECEI signal.