H-mode: Difference between revisions
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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 the consequence of the suppression of turbulence in the edge plasma, induced by 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> | |||
The sheared flow is generated by the turbulence itself via the Reynolds Stress mechanism. | The sheared flow is generated by the turbulence itself via the Reynolds Stress mechanism. | ||
<ref>[http://dx.doi.org/10.1088/0741-3335/ | <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> | ||
Thus, the H-mode is the consequence of a self-organizing process in the plasma. | Thus, the H-mode is the consequence of a self-organizing process in the plasma. | ||
The details of this mechanism are the subject of ongoing studies. | The details of this mechanism are the subject of ongoing studies. | ||
Revision as of 22:53, 25 August 2009
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. [1] In the H-mode, the energy confinement time is significantly enhanced, i.e., typically by a factor of 2 or more. [2]
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. The local suppression of turbulence leads to a reduction of transport and a steepening of the edge profiles. [3] The sheared flow is generated by the turbulence itself via the Reynolds Stress mechanism. [4] Thus, the H-mode is the consequence of a self-organizing process in the plasma. The details of this mechanism are the subject of ongoing studies. [5]
ELMs
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. [6] Although Quiescent H-modes exist (without ELMs), they are considered not convenient due to the accumulation of impurities. 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. [7]
References
- ↑ F. Wagner et al, Development of an Edge Transport Barrier at the H-Mode Transition of ASDEX, Phys. Rev. Lett. 53 (1984) 1453 - 1456
- ↑ M. Keilhacker, H-mode confinement in tokamaks, Plasma Phys. Control. Fusion 29 (1987) 1401-1413
- ↑ F. Wagner, A quarter-century of H-mode studies, Plasma Phys. Control. Fusion 49 (2007) B1-B33
- ↑ S.B. Korsholm et al, Reynolds stress and shear flow generation, Plasma Phys. Control. Fusion 43 (2001) 1377-1395
- ↑ M.A. Malkov and P.H. Diamond, Weak hysteresis in a simplified model of the L-H transition, Phys. Plasmas 16 (2009) 012504
- ↑ D.N. Hill, A review of ELMs in divertor tokamaks, Journal of Nuclear Materials 241-243 (1997) 182-198
- ↑ 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