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Transition to subcr...
Transition to subcritical turbulence in a tokamak plasma
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- van Wyk, F (författare)
- University Of Oxford,Culham Science Centre,Daresbury Laboratory
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- Hood Highcock, Edmund, 1985 (författare)
- Chalmers tekniska högskola,Chalmers University of Technology
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- Schekochihin, AA (författare)
- Merton College,University Of Oxford
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- Roach, C. M. (författare)
- Culham Science Centre
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- Field, AR (författare)
- Culham Science Centre
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- Dorland, William D. (författare)
- University of Maryland,University Of Oxford
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(creator_code:org_t)
- 2016
- 2016
- Engelska.
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 82:6
- Relaterad länk:
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http://dx.doi.org/10...
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https://research.cha...
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https://doi.org/10.1...
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Abstract
Ämnesord
Stäng
- Tokamak turbulence, driven by the ion-temperature gradient and occurring in the presence of flow shear, is investigated by means of local, ion-scale, electrostatic gyrokinetic simulations (with both kinetic ions and electrons) of the conditions in the outer core of the Mega-Ampere Spherical Tokamak (MAST). A parameter scan in the local values of the ion-temperature gradient and flow shear is performed. It is demonstrated that the experimentally observed state is near the stability threshold and that this stability threshold is nonlinear: sheared turbulence is subcritical, i.e. the system is formally stable to small perturbations, but, given a large enough initial perturbation, it transitions to a turbulent state. A scenario for such a transition is proposed and supported by numerical results: close to threshold, the nonlinear saturated state and the associated anomalous heat transport are dominated by long-lived coherent structures, which drift across the domain, have finite amplitudes, but are not volume filling; as the system is taken away from the threshold into the more unstable regime, the number of these structures increases until they overlap and a more conventional chaotic state emerges. Whereas this appears to represent a new scenario for transition to turbulence in tokamak plasmas, it is reminiscent of the behaviour of other subcritically turbulent systems, e.g. pipe flows and Keplerian magnetorotational accretion flows.
Ämnesord
- NATURVETENSKAP -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)
Nyckelord
- fusion plasma
- plasma simulation
- plasma instabilities
Publikations- och innehållstyp
- art (ämneskategori)
- ref (ämneskategori)
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