Speaker
Xiang Han
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1105.pdf
Experimental charaterization of a quasi-coherent turbulence structure in
the edge plasmas in W7-X
X. Han1 , A. Krämer-Flecken1 , T. Windisch2 , S. Liu1 , Y. Liang1 , M. Rack1 , P. Drews1 ,
J. Cosfeld1 , Y. Gao1 , G. Fuchert2 , J. Geiger2 , O. Grulke2 , and the W7-X team
1 Institute für Energie-und Klimaforschung - Plasmaphysik, Forschungszentrum Jülich, 52425
Jülich, Germany
2 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
A quasi-coherent turbulence structure (QC mode) in a frequency range of 10 kHz to 25 kHz
has been studied by measuring the electron density fluctuation via a hopping Poloidal Corre-
lation Reflectometer (PCR) [1, 2] in W7-X. It is observed in the standard and narrow mirror
configurations, and absence in the high-iota configuration, which implies a certain dependence
of the QC mode on the edge rotational transform. The QC-mode appears in the edge region
accompanied by a steep electron density gradient inside the last-closed flux surface (LCFS).
Its initial typical frequency of 25 kHz decreases to 10 kHz when the probing position moves
toward the core. By calculating the cross correlation spectrum within each of the two antennae
combination, the poloidal wavenumber of the QC mode is estimated to be kθ ≈ −0.21cm−1
propagating in the electron diamagnetic drift direction. The turbulence rotation velocity in this
standard configuration is vturb ≈ 8.4km/s in the laboratory frame, which is consistent with the
result from the slope of the cross-phase spectrum. With the edge electron temperature and the
magnetic field in the edge region, the gyroradius at the sound speed of the QC-mode is calcu-
lated to be ρs ≈ 0.207, and kθ ρs ≈ 0.145. This is qualitatively demonstrates that the QC-mode
is in the range expected for drift- waves. Evidence shows that the existence of the QC-mode
might be influenced by the edge radiation level, also the turbulence in the low frequency range
( f < 10kHz) is suppressed when the QC-mode exists.
Acknowledgment
This work has been carried out within the framework of the EUROfusion Consortium and
has received funding from the European Union’s Horizon 2020 research and innovation pro-
gramme under grant agreement number 633053. The views and opinions expressed herein do
not necessarily reflect those of the European Commission.
References
[1] A. Krämer-Flecken et al, Nucl. Fusion 57, 066023 (2017)
[2] T. Windisch et al, Plasma Phys. Control. Fusion 59, 105002 (2017)
