Open Access2D measurements of parallel counter-streaming flows in the W7-X scrape-off layer for attached and detached plasmas
Author(s) -
V. Perseo,
V. Winters,
Y. Feng,
F. Reimold,
O. Ford,
R. König,
S. Bozhenkov,
K. J. Brunner,
R. Burhenn,
P. Drewelow,
D.A. Ennis,
Yu Gao,
D. Gradic,
P. Hacker,
U. Hergenhahn,
M. Jakubowski,
J. Knauer,
T. Kremeyer,
D. M. Kriete,
M. Krychowiak,
S. Kwak,
H. Niemann,
A. Pavone,
F. Pisano,
A. Puig Sitjes,
G. Schlisio,
J. Svensson,
D. Zhang,
T. S. Pedersen
Publication year - 2021
Publication title -
nuclear fusion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.774
H-Index - 120
eISSN - 1741-4326
pISSN - 0029-5515
DOI - 10.1088/1741-4326/ac277a
Subject(s) - stellarator , plasma , impurity , ion , atomic physics , electron temperature , flow velocity , line (geometry) , electron density , intensity (physics) , plasma parameters , electron , physics , materials science , flow (mathematics) , optics , mechanics , nuclear physics , geometry , mathematics , quantum mechanics
Investigations of particle parallel flow velocities have been carried out for the scrape-off layer (SOL) of the Wendelstein 7-X (W7-X) stellarator, in order to gain insights on the SOL transport properties during attached and detached plasma scenarios. The experimental evidence is based on the coherence imaging spectroscopy (CIS) diagnostic, able to measure 2D impurity emission intensity and flow velocity. The impurity monitored by CIS is C 2+ , characterized by a line-emission intensity observed to be linearly proportional to the total plasma radiated power in both attached and detached plasmas. The related C 2+ velocity shows a strong dependence on the line-averaged electron density while remaining insensitive to the input power. During attached plasmas, the velocity increases with increasing line-averaged density. The tendency reverses in the transition to and during detachment, in which the velocity decreases by at least a factor of 2. The sharp drop in velocity, together with a rise in line-emission intensity, is reliably correlated to the detachment transition and can therefore be used as one of its signatures. The impurity flow velocity appears to be well coupled with the main ions’ one, thus implying the dominant role of impurity-main ion friction in the parallelimpurity transport dynamics. In view of this SOL impurity transport regime, the CIS measurement results are here interpreted with the help of EMC3-Eirene simulations, and their major trends are already explainable with a simple 1D fluid model.