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Simple advecting structures and the edge of chaos in subcritical tokamak plasmas
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McMillan, Ben F., Pringle, Chris C. T. and Teaca, Bogdan (2018) Simple advecting structures and the edge of chaos in subcritical tokamak plasmas. Journal of Plasma Physics, 84 (6). 905840611. doi:10.1017/S0022377818001216 ISSN 0022-3778.
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Official URL: http://dx.doi.org/10.1017/S0022377818001216
Abstract
In tokamak plasmas, sheared flows perpendicular to the driving temperature gradients can strongly stabilise linear modes. While the system is linearly stable, regimes with persistent nonlinear turbulence may develop, i.e. the system is subcritical. A perturbation with small but finite amplitude may be sufficient to push the plasma into a regime where nonlinear effects are dominant and thus allow sustained turbulence. The minimum threshold for nonlinear instability to be triggered provides a criterion for assessing whether a tokamak is likely to stay in the quiescent (laminar) regime. At the critical amplitude, instead of transitioning to the turbulent regime or decaying to a laminar state, the trajectory will map out the edge of chaos. Surprisingly, a quasi-travelling-wave solution is found as an attractor on this edge manifold. This simple advecting solution is qualitatively similar to, but simpler than, the avalanche-like bursts seen in earlier turbulent simulations and provides an insight into how turbulence is sustained in subcritical plasma systems. For large flow shearing rate, the system is only convectively unstable, and given a localised initial perturbation, will eventually return to a laminar state at a fixed spatial location.
Item Type: | Journal Article | ||||||||
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Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||||
Journal or Publication Title: | Journal of Plasma Physics | ||||||||
Publisher: | Cambridge University Press | ||||||||
ISSN: | 0022-3778 | ||||||||
Official Date: | 2018 | ||||||||
Dates: |
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Volume: | 84 | ||||||||
Number: | 6 | ||||||||
Article Number: | 905840611 | ||||||||
DOI: | 10.1017/S0022377818001216 | ||||||||
Status: | Peer Reviewed | ||||||||
Publication Status: | Published | ||||||||
Reuse Statement (publisher, data, author rights): | This article has been published in a revised form in Journal of Plasma Physics http://doi.org/10.1017/S0022377818001216. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works. © Cambridge University Press 2018 | ||||||||
Access rights to Published version: | Restricted or Subscription Access | ||||||||
Date of first compliant deposit: | 7 February 2020 | ||||||||
Date of first compliant Open Access: | 7 February 2020 | ||||||||
Open Access Version: |
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