Speaker
Katerina Jirakova
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1081.pdf
Parallel SOL transport regime in tokamak COMPASS
K. Jirakova1,2 , J. Seidl1 , J. Adamek1 , P. Bilkova1 , J. Cavalier 1 , J. Horacek1 , M. Komm1
1 Institute of Plasma Physics, Czech Academy of Sciences, Prague
2 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Prague
The topic of parallel SOL transport regimes is of great interest for future fusion devices, as
the detached or partially detached regimes allow to reduce heat fluxes incident on the diver-
tor targets by dissipating a substantial part of the energy carried by plasma particles. Tokamak
COMPASS is well suited for SOL transport studies, possessing an advanced system of diag-
nostics such as a divertor probe array capable of measuring heat fluxes with high temporal
resolution [1]. However, due to its short connection length (R ≈ 3 m) and open divertor con-
figuration, it is not clear which transport regime tokamak COMPASS operates in. This study
addresses the question based on an analysis of electron temperature profiles.
Using the vertical and horizontal reciprocating probe, the divertor probe array, and the High
Resolution Thomson Scattering diagnostics, electron temperature profiles are measured at three
poloidal locations: the plasma top, the outer midplane, and the divertor. Position of the separa-
trix, whose accurate knowledge is crucial for the analysis, is discussed in depth. The resulting
profiles are compared in the view of the two-point model [2], providing an estimate of par-
allel temperature gradient and plasma collisionality. By processing the database of tokamak
COMPASS discharges, a scan over plasma parameters such as plasma current or line-averaged
density is performed, yielding operational space in which partial detachment plays a role.
COMPASS Scrape-Off Layer is shown to be typically in the sheath-limited regime or in
the transition region between the sheath-limited and conduction-limited regimes. This has im-
plications on the behavior of both the upstream and downstream temperatures. While in the
conduction-limited regime the upstream separatrix temperature is expected to be largely insen-
sitive to plasma conditions [2] [3], in the sheath-limited regime it decreases with increasing
plasma density. Since at low collisionalities the downstream temperature closely follows the
upstream one, a significant drop of target temperatures at high density, observed on COMPASS
in [4], must be treated with great care before it can be considered as a sign of detachment.
References
[1] J. Adamek et al, Nuclear Fusion 57 116017 (2017)
[2] P. C. Stangeby, The Plasma Boundary of Magnetic Fusion Devices, IOP Publishing Ltd, 2000, section 5.2
[3] G. D. Porter et al, Physics of Plasmas 5, 1410 (1998)
[4] M. Komm et al, 45th Conference on Plasma Physics (2018)
