Recent progress towards a physics-based understanding of the H-mode transition
| Autor: | Amanda Hubbard, Patrick Diamond, Istvan Cziegler, J. W. Hughes, George Tynan, James Irby, Mikhail Malkov, J. L. Terry |
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| Jazyk: | angličtina |
| Rok vydání: | 2016 |
| Předmět: |
Physics
Turbulence K-epsilon turbulence model turbulence Atmospheric-pressure plasma Reynolds stress Mechanics Condensed Matter Physics 01 natural sciences h-mode L-H transition 010305 fluids & plasmas Physics::Fluid Dynamics Nuclear Energy and Engineering Heat flux 0103 physical sciences Turbulence kinetic energy Statistical physics predator-prey 010306 general physics Shear flow Pressure gradient |
| Zdroj: | Tynan, GR; Cziegler, I; Diamond, PH; Malkov, M; Hubbard, A; Hughes, JW; et al.(2016). Recent progress towards a physics-based understanding of the H-mode transition. PLASMA PHYSICS AND CONTROLLED FUSION, 58(4). doi: 10.1088/0741-3335/58/4/044003. UC San Diego: Retrieved from: http://www.escholarship.org/uc/item/0q27v8d9 |
| ISSN: | 1361-6587 |
| Popis: | Results from recent experiment and numerical simulation point towards a picture of the L-H transition in which edge shear flows interacting with edge turbulence create the conditions needed to produce a non-zero turbulent Reynolds stress at and just inside the LCFS during L-mode discharges. This stress acts to reinforce the shear flow at this location and the flow drive gets stronger as heating is increased. The L-H transition ensues when the rate of work done by this stress is strong enough to drive the shear flow to large values, which then grows at the expense of the turbulence intensity. The drop in turbulence intensity momentarily reduces the heat flux across the magnetic flux surface, which then allows the edge plasma pressure gradient to build. A sufficiently strong ion pressure gradient then locks in the H-mode state. These results are in general agreement with previously published reduced 0D and 1D predator prey models. An extended predator-prey model including separate ion and electron heat channels yields a non-monotonic power threshold dependence on plasma density provided that the fraction of heat deposited on the ions increases with plasma density. Possible mechanisms to explain other macroscopic transition threshold criteria are identified. A number of open questions and unexplained observations are identified, and must be addressed and resolved in order to build a physics-based model that can yield predictions of the macroscopic conditions needed for accessing H-mode. |
| Databáze: | OpenAIRE |
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