Edge Localized Modes: Difference between revisions

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The steep edge gradients (of density and temperature) associated with an [[H-mode]] lead to quasi-periodic violent relaxation phenomena, known as Edge Localized Modes (ELMs), which have a strong impact on the surrounding vessel.
The steep edge gradients (of density and temperature) associated with an [[H-mode]] lead to quasi-periodic violent relaxation phenomena, known as Edge Localized Modes (ELMs), which have a strong impact on the surrounding vessel.
<ref>[http://dx.doi.org/10.1088/0741-3335/38/2/001 H. Zohm, ''Edge localized modes (ELMs)'', Plasma Phys. Control. Fusion '''38''' (1996) 105-128]</ref>
<ref>H. Zohm, ''Edge localized modes (ELMs)'', [[doi:10.1088/0741-3335/38/2/001|Plasma Phys. Control. Fusion '''38''' (1996) 105-128]]</ref>
<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>D.N. Hill, ''A review of ELMs in divertor tokamaks'', [[doi:10.1016/S0022-3115(97)80039-6 Journal of Nuclear Materials '''241-243''' (1997) 182-198]]</ref>


== Physical mechanism ==
== Physical mechanism ==
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The physical mechanism of ELMs has not been fully clarified. Several possible explanations have been put forward:
The physical mechanism of ELMs has not been fully clarified. Several possible explanations have been put forward:
* Nonlinear interchange modes <ref>A. Takayama and M. Wakatani, ''ELM modelling based on the nonlinear interchange mode in edge plasma'', [[doi:10.1088/0741-3335/38/8/046|Plasma Phys. Control. Fusion '''38''' (1996) 1411-1414]]</ref>
* Nonlinear interchange modes <ref>A. Takayama and M. Wakatani, ''ELM modelling based on the nonlinear interchange mode in edge plasma'', [[doi:10.1088/0741-3335/38/8/046|Plasma Phys. Control. Fusion '''38''' (1996) 1411-1414]]</ref>
* Coupled [[peeling-ballooning modes]] <ref>J.W. Connor et al, ''Magnetohydrodynamic stability of tokamak edge plasmas'', [http://link.aip.org/link/?PHPAEN/5/2687/1 Phys. Plasmas '''5''' (1998) 2687]</ref><ref>P.B. Snyder et al, ''Edge localized modes and the pedestal: A model based on coupled peeling–ballooning modes'', [http://link.aip.org/link/?PHPAEN/9/2037/1 Phys. Plasmas '''9''' (2002) 2037]</ref><ref>J.-S. Lönnroth et al, ''Predictive transport modelling of type I ELMy H-mode dynamics using a theory-motivated combined ballooning–peeling model'', [[doi:10.1088/0741-3335/46/8/003|Plasma Phys. Control. Fusion '''46''' (2004) 1197-1215]]</ref><ref>N. Hayashi et al, ''Integrated simulation of ELM energy loss and cycle in improved H-mode plasmas'', [[doi:10.1088/0029-5515/49/9/095015|Nucl. Fusion '''49''' (2009) 095015]]</ref>
* Coupled [[peeling-ballooning modes]] <ref>J.W. Connor et al, ''Magnetohydrodynamic stability of tokamak edge plasmas'', [[doi:10.1063/1.872956|Phys. Plasmas '''5''' (1998) 2687]]</ref><ref>P.B. Snyder et al, ''Edge localized modes and the pedestal: A model based on coupled peeling–ballooning modes'', [[doi:10.1063/1.1449463|Phys. Plasmas '''9''' (2002) 2037]]</ref><ref>J.-S. Lönnroth et al, ''Predictive transport modelling of type I ELMy H-mode dynamics using a theory-motivated combined ballooning–peeling model'', [[doi:10.1088/0741-3335/46/8/003|Plasma Phys. Control. Fusion '''46''' (2004) 1197-1215]]</ref><ref>N. Hayashi et al, ''Integrated simulation of ELM energy loss and cycle in improved H-mode plasmas'', [[doi:10.1088/0029-5515/49/9/095015|Nucl. Fusion '''49''' (2009) 095015]]</ref>
* Peeling modes <ref>C.G. Gimblett, ''Peeling mode relaxation ELM model'', [[doi:10.1063/1.2404542|AIP Conf. Proc. '''871''' (2006) 87-99]]</ref>
* Peeling modes <ref>C.G. Gimblett, ''Peeling mode relaxation ELM model'', [[doi:10.1063/1.2404542|AIP Conf. Proc. '''871''' (2006) 87-99]]</ref>
* Flux surface peeling <ref>E.R. Solano et al, ''ELMs and strike point jumps'', [[doi:10.1016/j.jnucmat.2004.09.067|Journal of Nuclear Materials '''337-339''' (2005) 747-750]]</ref>
* Flux surface peeling <ref>E.R. Solano et al, ''ELMs and strike point jumps'', [[doi:10.1016/j.jnucmat.2004.09.067|Journal of Nuclear Materials '''337-339''' (2005) 747-750]]</ref>
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The occurrence of an ELM leads to a significant expulsion of heat and particles, with deleterious consequences for the vessel wall and machine operation.
The occurrence of an ELM leads to a significant expulsion of heat and particles, with deleterious consequences for the vessel wall and machine operation.
Although [[Quiescent H-mode]]s exist (without ELMs),
Although [[Quiescent H-mode]]s exist (without ELMs),
<ref>[http://link.aip.org/link/?PHPAEN/12/056121/1 K.H. Burrell et al, ''Advances in understanding quiescent H-mode plasmas in DIII-D'', Phys. Plasmas '''12''' (2005) 056121]</ref>
<ref>K.H. Burrell et al, ''Advances in understanding quiescent H-mode plasmas in DIII-D'', [[doi:10.1063/1.1894745|Phys. Plasmas '''12''' (2005) 056121]]</ref>
they are generally considered not convenient due to the accumulation of [[impurities]].
they are generally 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.
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>
<ref>M.R. Wade, ''Physics and engineering issues associated with edge localized mode control in ITER'', [[doi:10.1016/j.fusengdes.2009.01.063|Fusion Engineering and Design '''84''', Issues 2-6 (2009) 178-185]]</ref>


== See also ==
== See also ==

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