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Oct 13 – 18, 2014
Hotel Park Inn Pribaltiyskaya
Europe/Moscow timezone

Can Gyrokinetics Really Describe Transport in L-Mode Core Plasmas?

Oct 14, 2014, 2:00 PM
4h 45m
Green 8-9 (Hotel Park Inn Pribaltiyskaya)

Green 8-9

Hotel Park Inn Pribaltiyskaya

Saint Petersburg, Russian Federation
Poster Poster 2

Speaker

Prof. Frank Jenko (IPP Garching)

Description

The common view in fusion theory is that nonlinear gyrokinetics constitutes a reliable first-principles approach to describe turbulent transport in MCF devices. Surprisingly, however, two recent findings challenged this notion. First, the experimental ion heat fluxes in the outer core of certain DIII-D L-mode discharges were underpredicted by GK simulations by almost an order of magnitude. This finding has been dubbed the „shortfall problem“ and has triggered extensive theoretical efforts on an international level. Second, a careful analysis of some L-mode discharges in the JET tokamak revealed a significant reduction of ion temperature profile stiffness in the presence of strong NBI [1]. This was first attributed to a combination of high toroidal flow shear and low magnetic shear. However, nonlinear GK simulations failed to confirm this suspicion, overpredicting the observed fluxes by up to an order of magnitude. This finding could be called the „excess problem“ and is as severe as the shortfall problem described above. The main goal of the present contribution is to revisit both of these problems and substantiate or refute them. At stake is the plasma theory community’s confidence to devise a predictive transport capability for devices like ITER or DEMO on the basis of nonlinear GK. Via careful studies with the GENE code (using about 30 million CPUh), both of these challenges could be met successfully. While the transport levels in outer-core L-mode discharges of DIII-D, C-Mod, and ASDEX Upgrade [2] can be reproduced within the experimental error bars, the observed ion temperature stiffness reduction in JET can be explained in terms of nonlinear electromagnetic effects in the presence of fast ions [3]. Thus, a number of ideas about possible elements missing in the present theoretical description or even a possible breakdown of GK are identified as premature. Meanwhile, these studies highlight the fact that the search for adequate minimal models of turbulent plasma transport under various experimental circumstances is highly non-trivial. [1] Mantica, PRL 107, 135004 (2011) [2] Told, PoP 20, 122312 (2013) [3] Citrin, PRL 111, 155001 (2013) This work was supported by EURATOM and carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
Paper Number TH/P2-7
Country or International Organisation Germany

Primary author

Prof. Frank Jenko (IPP Garching)

Co-authors

Dr Alejandro Banon Navarro (IPP Garching) Prof. Anne White (MIT) Dr Clarisse Bourdelle (CEA) Dr Daniel Told (IPP Garching) Dr Dick Hogeweij (FOM Institute DIFFER) Dr Emiliano Fable (IPP Garching) Dr Francis Casson (CCFE) Dr Hauke Doerk (IPP Garching) Dr Jeremie Abiteboul (IPP Garching) Dr Jeronimo Garcia (CEA) Dr Jonathan Citrin (FOM Institute DIFFER) Dr Moritz Pueschel (University of Wisconsin-Madison) Dr Nathan Howard (MIT) Dr Paola Mantica (Istituto di Fisica del Plasma, Milano) Dr Remi Dumont (CEA) Dr Ron Bravenec (Fourth-State Research) Prof. Thomas Johnson (KTH Stockholm) Dr Tobias Goerler (IPP Garching) Dr Willem Haverkort (FOM Institute DIFFER)

Presentation materials