Speaker
Dr
Thomas Pütterich
(Max-Planck-Institut für Plasmaphysik)
Description
The radial electric field E_r at the plasma edge and its relation to plasma turbulence is investigated throughout the LH-transition and an ELM cycle. Various diagnostics are considered including an upgraded charge exchange recombination spectroscopy system. The latter is able to measure impurity temperature, flow and density profiles with a frequency of up to 20kHz and a radial resolution of down to 3 mm. This enables the comparison of E_r with the one calculated from neoclassical theory E_r,neo , taking toroidal flows into account. The events during which E_r is not explained by neoclassical theory are of special interest, as the difference indicates an additional mechanism such as turbulence driven zonal flows (ZF).
The occurrence of the latter is suggested by earlier investigations during the LH-transition performed at other tokamak experiments and also at ASDEX Upgrade. For the present study, the I-phase at the LH-transition was investigated. In the I-phase regular turbulent bursts and profile changes occur with a frequency of a few kHz interrupted by more quiet phases. If the turbulence drives ZFs an increased E_r versus E_r,neo is expected after the turbulent bursts, however, no significant discrepancies between E_r and E_r,neo are found indicating negligible contributions of ZFs. Additionally, a correlation analysis shows a simultaneous evolution of the measured E_r, E_r,neo and the turbulence and thus, a rise of the turbulence level prior to the flow generation as expected from predator-prey like turbulence-ZF interactions cannot be confirmed. Instead, the bursts during the I-phase show an ELM-type character. This observations suggest that E_r,neo causes the required ExB shearing for the LH-transition along the lines in [1]. In addition, at the LH-transition, the well in the E_r,neo-profile is found to deepen with increasing B_T, in agreement with P_LH ~ B_T while the ExB shear velocity (~ E_r/B) is constant.
In order to better understand the observations at the LH-transition the same comparison of E_r and E_r,neo is performed during a fully developed H-mode with type-I ELMs. It may be noted that during the I-phase the turbulence bursts do not reduce the E_r back to levels which are typical during L-mode, while during an H-mode the reduction of E_r during an ELM reduces E_r to levels which are observed in L-mode.
[1] Sauter,P. et al., NF 52,2012
| Country or International Organization | Germany |
|---|---|
| Paper Number | EX/P6-29 |
Primary author
Dr
Thomas Pütterich
(Max-Planck-Institut für Plasmaphysik)
Co-authors
Dr
Eleonora Viezzer
(Max-Planck-Institut fuer Plasmaphysik)
Dr
Elisabeth Wolfrum
(Max Planck Institut fuer Plasmaphysik)
Mr
Florian Laggner
(Institute of Applied Physics, TU Vienna)
Dr
Francois Ryter
(IPP-Garching)
Dr
Gregor Birkenmeier
(Max Planck Institute for Plasma Physics, Garching, Germany)
Mr
Marco Cavedon
(Max-Planck-Institut für Plasmaphysik)
Dr
Peter Manz
(Max-Planck Institut für Plasmaphysik)
Dr
Rachael McDermott
(Max Planck Institut für Plasmaphysik)
Dr
Ralph Dux
(Max-Planck-Institut für Plasmaphysik, Garching, Germany)
Dr
Tim Happel
(Max-Planck-Institut für Plasmaphysik)
Prof.
Ulrich Stroth
(Max-Planck-Institut für Plasmaphysik)
