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-When a magnetically confined plasma is heated strongly and a threshold heating power level is exceeded, it may spontaneously transition from a low confinement (or L-mode) state to a high confinement (or H-mode) state.
+When a magnetically confined plasma is heated strongly and a threshold heating power level is exceeded, it may spontaneously transition from a low confinement (or [[L-mode]]) state to a high confinement (or H-mode) state.
-<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.53.1453 F. Wagner et al, ''Development of an Edge Transport Barrier at the H-Mode Transition of ASDEX'', Phys. Rev. Lett. '''53''' (1984) 1453 - 1456]</ref>
+<ref>F. Wagner et al, ''Development of an Edge Transport Barrier at the H-Mode Transition of ASDEX'', [[doi:10.1103/PhysRevLett.53.1453|Phys. Rev. Lett. '''53''' (1984) 1453 - 1456]]</ref>
 In the H-mode, the [[Energy confinement time|energy confinement time]] is significantly enhanced, i.e., typically by a factor of 2 or more.
-<ref>[http://dx.doi.org/10.1088/0741-3335/29/10A/320 M. Keilhacker, ''H-mode confinement in tokamaks'', Plasma Phys. Control. Fusion '''29''' (1987) 1401-1413]</ref>
+<ref>M. Keilhacker, ''H-mode confinement in tokamaks'', [[doi:10.1088/0741-3335/29/10A/320|Plasma Phys. Control. Fusion '''29''' (1987) 1401-1413]]</ref>
+<ref>F. Wagner et al., ''H-mode of W7-AS stellarator'', [[doi:10.1088/0741-3335/36/7A/006|Plasma Phys. Control. Fusion '''36''' (1994) A61]]</ref>
+<ref>[http://efdasql.ipp.mpg.de/HmodePublic/ The International Global H-mode Confinement Database]</ref>
+H-mode profiles have a characteristic ''[[Pedestal|edge pedestal]]''.
 == Physical mechanism ==
-This transport bifurcation is the consequence of the suppression of turbulence in the edge plasma, induced by a sheared flow layer and an associated edge radial electric field.
+This transport bifurcation is due to the suppression of turbulence in the edge plasma.
-<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>
+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 precise mechanism governing this phenomenon is the subject of ongoing studies.
+The local suppression of turbulence leads to a reduction of transport and a steepening of the edge profiles.
+<ref>F. Wagner, ''A quarter-century of H-mode studies'', [[doi:10.1088/0741-3335/49/12B/S01|Plasma Phys. Control. Fusion '''49''' (2007) B1-B33]]</ref>
-== ELMs ==
+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. Simply put, transport generated by the fluctuations produces a radial current ''j<sub>r</sub>'' that spins up the plasma via the ''j'' &times; ''B'' [[:Wikipedia:Lorentz force|Lorentz force]]. <ref>P.H. Diamond and Y.-B. Kim, ''Theory of mean poloidal flow generation by turbulence'', [[doi:10.1063/1.859681|Phys. Fluids B '''3''' (1991) 1626]]</ref> <ref>S.B. Korsholm et al, ''Reynolds stress and shear flow generation'', [[doi:10.1088/0741-3335/43/10/308|Plasma Phys. Control. Fusion '''43''' (2001) 1377-1395]]</ref>
+* This radial current can also actively be produced by electrode biasing. <ref>R.J. Taylor et al, ''H-mode behavior induced by cross-field currents in a tokamak'', [[doi:10.1103/PhysRevLett.63.2365|Phys. Rev. Lett. '''63''' (1989) 2365-2368]]</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>H. Wobig and J. Kisslinger, ''Viscous damping of rotation in Wendelstein 7-AS'', [[doi:10.1088/0741-3335/42/7/306|Plasma Phys. Control. Fusion '''42''' (2000) 823-841]]</ref>
+* Sheared flow can also be generated by external momentum input.
-The steep edge gradients (of density and temperature) lead to quasi-periodic violent relaxation phenomena, known as Edge Localized Modes (ELMs), which have a strong impact on the surrounding vessel.
+The details of the feedback mechanism between turbulence and sheared flow are the subject of ongoing studies.
-<ref>[http://dx.doi.org/10.1016/S0022-3115(97)80039-6 D.N. Hill, ''A review of ELMs in divertor tokamaks'', Journal of Nuclear Materials '''241-243''' (1997) 182-198]</ref>
+<ref>P.H. Diamond et al, ''Self-Regulating Shear Flow Turbulence: A Paradigm for the L to H Transition'', [[doi:10.1103/PhysRevLett.72.2565|Phys. Rev. Lett. '''72''' (1994) 2565 - 2568]]</ref>
-Although Quiescent H-modes exist (without ELMs), they are considered not convenient due to the accumulation of impurities.
+<ref>M.A. Malkov and P.H. Diamond, ''Weak hysteresis in a simplified model of the L-H transition'', [[doi:10.1063/1.3062834|Phys. Plasmas '''16''' (2009) 012504]]</ref>
-To achieve steady state, an ELMy H-mode is preferred and this mode of operation is proposed as the standard operating scenario for [[ITER]], thus converting ELM mitigation into a priority.
-<ref>[http://dx.doi.org/10.1016/j.fusengdes.2009.01.063 M.R. Wade, ''Physics and engineering issues associated with edge localized mode control in ITER'', Fusion Engineering and Design '''84''', Issues 2-6 (2009) 178-185]</ref>
+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]].
+== See also ==
+* [[Edge Localized Modes]]
 == References ==
 <references />