Speaker
Ondrej Grover
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1096.pdf
Search for zonal structures on the radial electric field and Reynolds stress
profiles on COMPASS
O. Grover1,2 , J. Seidl1 , J. Adamek1 , P. Vondracek1,3 , M. Tomes1,3 , J. Havlicek1 , P. Junek1 ,
V. Weinzettl1 , M. Hron1 , R. Panek1 and the COMPASS team1
1 Institute of Plasma Physics, The Czech Academy of Sciences, Prague, Czech Republic
2 FNSPE, Czech Technical University in Prague, Czech Republic
3 Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
The recent observation of stationary zonal-flow-like structures on JET with Doppler back-
scattering [1] has motivated the search for similar structures in the radial electric field Er well
on COMPASS [5]. The diagnostic used on COMPASS is a complex probe head mounted on a
horizontal reciprocating manipulator on the outer midplane which enables a direct measurement
of Er as well as the radial-poloidal component of the Reynolds stress tensor Rrp . The Reynolds
stress has been identified in recent models and experiments [2] as a likely driver of poloidal
zonal flows which are expected to play a key role in the L-H transition and the associated limit
cycle oscillations (LCO) [3]. The probe head features both Langmuir and ball-pen probes [4]
which enables a correction for the effect of the electron temperature on measurements of Er .
It was demonstrated that the probe diagnostic can measure radial profiles of Er which cover
the full extent of the Er well and remain stationary during both the inward and outward recip-
rocations. The search for stationary structures on the Er profile was complicated by saw-teeth
crashes which modulate Er . For this reason, dedicated scenarios were developed. No stationary
zonal-flow-like structures have been observed when the Er well is so narrow that its radial scale
is comparable to the expected radial scale of the structures.
The probe diagnostic was also used to measure fluctuations of the density δ ne and the electric
field Er during LCO with a frequency of 2-5 kHz. The δ ne , Er evolution is found to be consistent
with type-J LCO [3] where the Er is mostly driven by the pressure gradient and not by the
Reynolds stress. The magnetic signature of the LCO is toroidally symmetric and propagates
from the LFS to the HFS, i.e. left-right asymmetric (as opposed to top-down on other devices).
References
[1] J. C. Hillesheim, E. Delabie, H. Meyer, et al., Physics Review Letters 116, 065002 (2016)
[2] G. R. Tynan, I. Cziegler, P. H. Diamond, et al., Plasma Physics and Controlled Fusion 58, 044003 (2016)
[3] J. Cheng, J. Dong, K. Itoh, et al., Nuclear Fusion 54 114004 (2014)
[4] J. Adamek, H. W. Müller, C. Silva, et al., Review of Scientific Instruments 87, 043510 (2016)
[5] R. Pánek, J. Adámek, M. Aftanas, et al., Plasma Physics and Controlled Fusion 58, 014015 (2016)
