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H-mode: Difference between revisions
→Physical mechanism
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== Physical mechanism == | == Physical mechanism == | ||
This transport bifurcation is the consequence of the suppression of turbulence in the edge plasma | This transport bifurcation is the consequence of the suppression of turbulence in the edge plasma. | ||
There is substantial evidence that the suppression of turbulence is the consequence of the formation of a sheared flow layer and an associated edge radial electric field. | |||
The local suppression of turbulence leads to a reduction of transport and a steepening of the edge profiles. | The local suppression of turbulence leads to a reduction of transport and a steepening of the edge profiles. | ||
<ref>[http://dx.doi.org/10.1088/0741-3335/49/12B/S01 F. Wagner, ''A quarter-century of H-mode studies'', Plasma Phys. Control. Fusion '''49''' (2007) B1-B33]</ref> | <ref>[http://dx.doi.org/10.1088/0741-3335/49/12B/S01 F. Wagner, ''A quarter-century of H-mode studies'', Plasma Phys. Control. Fusion '''49''' (2007) B1-B33]</ref> | ||
The sheared flow | |||
A variety of mechanisms can give rise to sheared flow. | |||
The main process for sheared flow generation is generation by the turbulence itself via the Reynolds Stress mechanism. | |||
<ref>[http://dx.doi.org/10.1088/0741-3335/43/10/308 S.B. Korsholm et al, ''Reynolds stress and shear flow generation'', Plasma Phys. Control. Fusion '''43''' (2001) 1377-1395]</ref> | <ref>[http://dx.doi.org/10.1088/0741-3335/43/10/308 S.B. Korsholm et al, ''Reynolds stress and shear flow generation'', Plasma Phys. Control. Fusion '''43''' (2001) 1377-1395]</ref> | ||
The details of | The details of the feedback mechanism between turbulence and sheared flow are the subject of ongoing studies. | ||
<ref>[http://link.aip.org/link/?PHPAEN/16/012504/1 M.A. Malkov and P.H. Diamond, ''Weak hysteresis in a simplified model of the L-H transition'', Phys. Plasmas '''16''' (2009) 012504]</ref> | <ref>[http://link.aip.org/link/?PHPAEN/16/012504/1 M.A. Malkov and P.H. Diamond, ''Weak hysteresis in a simplified model of the L-H transition'', Phys. Plasmas '''16''' (2009) 012504]</ref> | ||
However, other factors can also contribute, such as the viscous damping, which might explain the dependence on rational surfaces observed in the stellarator W7-AS. | However, other factors can also contribute, such as the viscous damping, which might explain the dependence on rational surfaces observed in the stellarator W7-AS. | ||
<ref>[http://dx.doi.org/10.1088/0741-3335/42/7/306 H. Wobig and J. Kisslinger, ''Viscous damping of rotation in Wendelstein 7-AS'', Plasma Phys. Control. Fusion '''42''' (2000) 823-841]</ref> | <ref>[http://dx.doi.org/10.1088/0741-3335/42/7/306 H. Wobig and J. Kisslinger, ''Viscous damping of rotation in Wendelstein 7-AS'', Plasma Phys. Control. Fusion '''42''' (2000) 823-841]</ref> | ||
Sheared flow can also be generated by imposing an external radial electric field (biasing), or by external momentum input. | |||
In summary, the H-mode is the consequence of a self-organizing process in the plasma. | |||
The mechanism is probably closely related to the mechanism for forming an [[Internal Transport Barrier]]. | The mechanism is probably closely related to the mechanism for forming an [[Internal Transport Barrier]]. | ||