Speaker:
Guilhem Dif-Pradalier
Institution:
CEA France
Date:
Tuesday, December 15, 2020
Time:
9:00 am
Location:
Zoom Seminar
Abstract:
For over three decades, the observation of rapid core confinement improvement upon favourable modifications of edge operating conditions has been a nagging source of puzzlement for experimentalists investigating conditions for a lasting source of fusion energy in tokamaks [1]. The transport properties of drift-wave/interchange turbulence and the interaction of the confined plasma with its material boundaries have long been recognised as essential to the resolution of this conundrum [2]. Key aspects of the turbulent
dynamics in the plasma edge are poorly quantified, owing to the disparity of temporal and spatial scales and the inadequacy of performing scale separations. "First-principles" approaches are only really useful insofar as they test basic ideas or open avenues for basic understanding. It is in that spirit that, relaxing oft-made scale separation assumptions in the edge a narrow region at the interface between open and closed magnetic field lines seems central to explaining the transport properties of turbulence, on more global scales. This `not local’ influence is mediated through localised interactions with the material boundaries and is responsible for the emergence of a stable, localised and persistent transport barrier in the plasma edge. These results suggest a framework of understanding where turbulence is not only locally driven by the local gradients but centrally influenced by fluxes of turbulence activity, primarily though not exclusively coming from the edge [3,4]. In particular, we discuss vorticity-related mechanisms and their observed impact on transport barrier formation. These questions are certainly important in the perspective of accessing high confinement regimes, a central question for fusion.
References
dynamics in the plasma edge are poorly quantified, owing to the disparity of temporal and spatial scales and the inadequacy of performing scale separations. "First-principles" approaches are only really useful insofar as they test basic ideas or open avenues for basic understanding. It is in that spirit that, relaxing oft-made scale separation assumptions in the edge a narrow region at the interface between open and closed magnetic field lines seems central to explaining the transport properties of turbulence, on more global scales. This `not local’ influence is mediated through localised interactions with the material boundaries and is responsible for the emergence of a stable, localised and persistent transport barrier in the plasma edge. These results suggest a framework of understanding where turbulence is not only locally driven by the local gradients but centrally influenced by fluxes of turbulence activity, primarily though not exclusively coming from the edge [3,4]. In particular, we discuss vorticity-related mechanisms and their observed impact on transport barrier formation. These questions are certainly important in the perspective of accessing high confinement regimes, a central question for fusion.
References
[1] F. Wagner et al., Phys. Rev. Lett. 49, 1408 (1982)
[2] B.B. Kadomtsev. Tokamak Plasma: A Complex Physical System (London: IoP Publishing) (1992)
[3] X. Garbet et al., Nucl.Fusion 34, 963 (1994)
[4] R. Singh and P.H. Diamond, Phys. Plasmas 27, 042308 (2020)
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Host:
Pat Diamond, UCSD