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H-mode: Difference between revisions
→Physical mechanism
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<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> | ||
A variety of mechanisms can give rise to sheared flow | A variety of mechanisms can give rise to sheared flow, or favour its growth: | ||
The main process for sheared flow generation is generation by the turbulence itself via the [[Reynolds stress]] mechanism. | * The main process for sheared flow generation is generation by the turbulence itself via the [[Reynolds stress]] mechanism. Simply put, transport generated by the fluctuations produces a radial current ''j<sub>r</sub>'' that spins up the plasma via the ''j'' × ''B'' [[:Wikipedia:Lorentz force|Lorentz force]]. <ref>[http://dx.doi.org/10.1063/1.859681 P.H. Diamond and Y.-B. Kim, ''Theory of mean poloidal flow generation by turbulence'', Phys. Fluids B '''3''' (1991) 1626]</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> | ||
Simply put, transport generated by the fluctuations produces a radial current ''j<sub>r</sub>'' that spins up the plasma via the ''j'' × ''B'' [[:Wikipedia:Lorentz force|Lorentz force]]. | * This radial current can also actively be produced by electrode biasing. <ref>[http://link.aps.org/doi/10.1103/PhysRevLett.63.2365 R.J. Taylor et al, ''H-mode behavior induced by cross-field currents in a tokamak'', Phys. Rev. Lett. '''63''' (1989) 2365-2368]</ref> | ||
<ref>[http://dx.doi.org/10.1063/1.859681 P.H. Diamond and Y.-B. Kim, ''Theory of mean poloidal flow generation by turbulence'', Phys. Fluids B '''3''' (1991) 1626]</ref> | * Sheared flow may be favoured by reduced 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/10.1088/0741-3335/43/10/308 S.B. Korsholm et al, ''Reynolds stress and shear flow generation'', Plasma Phys. Control. Fusion '''43''' (2001) 1377-1395]</ref> | * Sheared flow can also be generated by external momentum input. | ||
This radial current can also actively be produced by electrode biasing. | |||
<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.63.2365 R.J. Taylor et al, ''H-mode behavior induced by cross-field currents in a tokamak'', Phys. Rev. Lett. '''63''' (1989) 2365-2368]</ref> | |||
The details of the feedback mechanism between turbulence and sheared flow are the subject of ongoing studies. | The details of the feedback mechanism between turbulence and sheared flow are the subject of ongoing studies. | ||
<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.72.2565 P.H. Diamond et al, ''Self-Regulating Shear Flow Turbulence: A Paradigm for the L to H Transition'', Phys. Rev. Lett. '''72''' (1994) 2565 - 2568]</ref> | <ref>[http://link.aps.org/doi/10.1103/PhysRevLett.72.2565 P.H. Diamond et al, ''Self-Regulating Shear Flow Turbulence: A Paradigm for the L to H Transition'', Phys. Rev. Lett. '''72''' (1994) 2565 - 2568]</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> | <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> | ||
In summary, the H-mode is the consequence of a self-organizing process in the plasma. | In summary, the H-mode is the consequence of a self-organizing process in the plasma. | ||