Speaker
Gustavo Guedes Grenfell
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1101.pdf
2-D filament dynamics in high and low shear flows in the edge of the
RFX-mod tokamak
G. Grenfell, M. Spolaore, M. Agostini, L. Carraro, R. Cavazzana, L. Cordaro,
G. De Masi, P. Franz, L. Marrelli, E. Martines, B. Momo, M. E. Puiatti, P. Scarin,
S. Spagnolo, N. Vianello, B. Zaniol, M. Zuin and the RFX-mod Team
Consorzio RFX, 35127, Padova, Italy
The edge and Scrape-Off-Layer (SOL) transport is dominated by filaments [1]. They can
carry turbulent energy from the edge to the SOL, impacting the local SOL fluctuation and en-
hancing the interaction with plasma-facing components. In addition, they can affect the SOL
decay width, by increasing the cross-field transport, which can be a critical issue for future
fusion reactors [2]. On the other hand, filaments can be strongly modified by the background
shear flow, as well as modify it [3]. In this work, we study the filaments dynamic in differ-
ent background shear flows using a set of 2-D electrostatic and magnetic sensors array in the
plasma edge of the RFX-mod device operated as a tokamak. In addition, first wall poloidally
symmetric electrostatic sensors. Through advanced statistical techniques, we detect filaments
in different scales and track them from the edge to the SOL, in a 2-D floating potential map.
Filaments relevant parameters are computed in the proper plasma frame (in contrast to the labo-
ratory frame) and compared for different scenarios, including ohmic L-mode to H-mode ELMy
and ELM-free, the latter induced by edge electrode biasing technique [4]. Their measured fea-
tures in the different scenarios are compared and discussed in the framework of theoretical and
simulation predictions [3]. In L-mode, their radial velocity and size at near SOL region, close
to separatrix, are typically vr ≈ 2 km/s, δr ≈ 10 mm and δθ ≈ 15 mm, so their convection time
(δr2 /(vr δθ ) ≈ 4 µs) is shorter than the shear time (B/dEr /dr ≈ 100 µs). In contrast, during the
ELM-free H-mode, the shear time is ≈ 2 µs, so only smaller and/or faster filaments survive.
Whereas, in the ELMs phase, the relaxation of the transport barrier allows bigger and/or slower
structures to endure the background flow shear. Finally, the role of the sheath connection for
the three scenarios is addressed, highlighting the potential structure tilt angle and ellipticity as
function of the radius and the measurement of the local parallel density current.
References
[1] D. A. D’Ippolito et al. Phys. Plasmas 18.6 (2011): 060501
[2] J. Horacek et al. Plasma Phys. Control. 58.7 (2016): 074005
[3] Myra, J. R., et al. Nucl. Fusion 53.7 (2013): 073013
[4] M. Spolaore et al. Nucl. Fusion 57.11 (2017): 116039.
