Transition to subcritical turbulence in a tokamak plasma
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...
| Main Authors: | , , , , , |
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| Format: | Journal article |
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Cambridge University Press
2016
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| _version_ | 1797091278756773888 |
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| author | van Wyk, F Highcock, E Schekochihin, A Roach, C Field, A Dorland, W |
| author_facet | van Wyk, F Highcock, E Schekochihin, A Roach, C Field, A Dorland, W |
| author_sort | van Wyk, F |
| collection | OXFORD |
| description | 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. |
| first_indexed | 2024-03-07T03:30:41Z |
| format | Journal article |
| id | oxford-uuid:ba9c6b79-88c7-4e34-b9a1-bb8f5d9e916f |
| institution | University of Oxford |
| last_indexed | 2024-03-07T03:30:41Z |
| publishDate | 2016 |
| publisher | Cambridge University Press |
| record_format | dspace |
| spelling | oxford-uuid:ba9c6b79-88c7-4e34-b9a1-bb8f5d9e916f2022-03-27T05:11:04ZTransition to subcritical turbulence in a tokamak plasmaJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:ba9c6b79-88c7-4e34-b9a1-bb8f5d9e916fSymplectic Elements at OxfordCambridge University Press2016van Wyk, FHighcock, ESchekochihin, ARoach, CField, ADorland, WTokamak 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. |
| spellingShingle | van Wyk, F Highcock, E Schekochihin, A Roach, C Field, A Dorland, W Transition to subcritical turbulence in a tokamak plasma |
| title | Transition to subcritical turbulence in a tokamak plasma |
| title_full | Transition to subcritical turbulence in a tokamak plasma |
| title_fullStr | Transition to subcritical turbulence in a tokamak plasma |
| title_full_unstemmed | Transition to subcritical turbulence in a tokamak plasma |
| title_short | Transition to subcritical turbulence in a tokamak plasma |
| title_sort | transition to subcritical turbulence in a tokamak plasma |
| work_keys_str_mv | AT vanwykf transitiontosubcriticalturbulenceinatokamakplasma AT highcocke transitiontosubcriticalturbulenceinatokamakplasma AT schekochihina transitiontosubcriticalturbulenceinatokamakplasma AT roachc transitiontosubcriticalturbulenceinatokamakplasma AT fielda transitiontosubcriticalturbulenceinatokamakplasma AT dorlandw transitiontosubcriticalturbulenceinatokamakplasma |