Speaker
Miglena Dimitrova
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1006.pdf
EEDF in the COMPASS divertor region during an impurity-seeding
experiment
M. Dimitrova1,2, Tsv. K. Popov3, M. Komm1, R. Dejarnac1, J. Stöckel1, V. Weinzettl1,
P. Vondracek1,4, P. Hacek1,4, M. Hron1, R. Panek1, the COMPASS team
and the EUROfusion MST1 Team5
1
Institute of Plasma Physics, The Czech Academy of Sciences, Prague, Czech Republic
2
Emil Djakov Institute of Electronics, Bulgarian Academy of Sciences, Sofia, Bulgaria
3
Faculty of Physics, St. Kl. Ohridski University of Sofia, Sofia, Bulgaria
4
Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
5
See author list in H. Meyer et al., Nuclear Fusion 57 102014 (2017)
This work presents results from swept Langmuir probe measurements in the divertor region of
the COMPASS tokamak [1] in D-shaped, L-mode deuterium discharges, with toroidal
magnetic field BT = -1.38 T, plasma current, Ipl = 210 kA and line-average electron density
4×1019 m-3. The electron energy distribution function (EEDF) was studied during a
detachment experiment with nitrogen injected into the divertor region.
The measured current-voltage probe characteristics were processed using the first-derivative
probe technique [2]. This technique allows to evaluate the plasma potential and the real
electron energy distribution function (respectively, the electron temperature and density).
In the divertor region of the COMPASS tokamak, the EEDF of the attached plasma usually
deviates from Maxwellian [3], but it can be approximate by a sum of two Maxwellian
distributions (bi-Maxwellian EEDF) with a low-energy electron population with temperatures
3.5-5 eV and a high-energy electron group with temperatures 10-25 eV.
During the nitrogen seeding, the EEDF changes to Maxwellian with temperatures 3.5-7 eV.
The hypothesis that the fast electrons relax via inelastic collisions with N2 and a Maxwellian
EEDF is formed will be discussed during the presentation.
The poloidal profiles of the plasma potential, electron temperatures and densities are
presented and used for calculation of the parallel power-flux density distribution in the
divertor region of the COMPASS tokamak before and during the nitrogen seeding.
References:
[1] R. Panek R et al.: Plasma Phys. Control. Fusion, Vol. 58 (2016), 014015.
[2] Tsv. K. Popov et al.: Plasma Phys. Control. Fusion, Vol. 51 (2009), 065014.
[3] M. Dimitrova et al.: Contrib. Plasma Phys., Vol. 54, No. 3 (2014), 255 – 260.
