Speaker
Javier Hernandez Nicolau
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1108.pdf
Detection of filamentary structrures using transfer entropy in TJ-II and
W7-X
J H. Nicolau1 , L. García1 , B. A. Carreras1 , B.Ph. van Milligen2 , B.Liu3 , G. Grenfell2,4 ,
U. Losada2 , C. Hidalgo2 and the TJ-II Team
1 Universidad Carlos III de Madrid, 28911 Leganés, Spain
2 Laboratorio Nacional de Fusion, CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain
3 Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong
University, Chengdu, People’s Republic of China
4 Consorzio RFX, Corso Stati Uniti 4, 35127, Padova, Italy
A new method to detect filamentary structures in magnetic confined plasmas is presented. The
method, transfer entropy (TE), is a technique which detects causality between signals [1][2]. It
measures information flow from different signals. In this work, it is applied to probes distributed
at different locations in the plasma. The results show connexions between signals with some
time lag. Thus, the TE is capable of detecting when the filaments are passing through distant
probes.
We apply the TE to the fluctuating electrostatic potential in
a resistive MHD model. Probes distributed along the poloidal
direction identify the periodicity of the filament. Furthermore,
knowing the periodicity allow us to calculate the length of
the filament. The directionality of TE is used to obtain their
poloidal velocity. Finally, the radial width of filaments is calcu-
lated by probes distributed along the radial direction. Figure 1: Filamentary structure
The method is applied to TJ-II and W7-X devices. Both ma- in TJ-II
chines have low magnetic shear which generates low order ra-
tional surfaces that dominate a wide radial region. In our simulations, filaments have the same
periodicity as the rational surfaces and they are rotating with the same poloidal velocity as
the plasma. This well-known characteristic helps to detect and contrast the filaments using the
present method. Our results are consistent with expected values and with recent experiments in
TJ-II [3].
References
[1] Schreiber T. 2000 Measuring information transfer. Phys. Rev. Lett. 85 461
[2] B.Ph. van Milligen et al. Causality detection and turbulence in fusion plasmas. 2014 Nucl. Fusion 54 023011
[3] B.Ph. van Milligen et al. Filaments in the edge confinement region of TJ-II. 2018 Nucl. Fusion 58, 026030
