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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>[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>
&lt;ref&gt;[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]&lt;/ref&gt;
<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>


== Physical mechanism ==
== Physical mechanism ==


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 &lt;ref&gt;[http://dx.doi.org/10.1088/0741-3335/38/8/046 A. Takayama and M. Wakatani, ''ELM modelling based on the nonlinear interchange mode in edge plasma'', Plasma Phys. Control. Fusion '''38''' (1996) 1411-1414]&lt;/ref&gt;
* Nonlinear interchange modes <ref>[http://dx.doi.org/10.1088/0741-3335/38/8/046 A. Takayama and M. Wakatani, ''ELM modelling based on the nonlinear interchange mode in edge plasma'', Plasma Phys. Control. Fusion '''38''' (1996) 1411-1414]</ref>
* Coupled peeling-ballooning modes &lt;ref&gt;[http://link.aip.org/link/?PHPAEN/5/2687/1 J.W. Connor et al, ''Magnetohydrodynamic stability of tokamak edge plasmas'', Phys. Plasmas '''5''' (1998) 2687]&lt;/ref&gt;&lt;ref&gt;[http://link.aip.org/link/?PHPAEN/9/2037/1 P.B. Snyder et al, ''Edge localized modes and the pedestal: A model based on coupled peeling–ballooning modes'', Phys. Plasmas '''9''' (2002) 2037]&lt;/ref&gt;&lt;ref&gt;[http://dx.doi.org/10.1088/0741-3335/46/8/003 J.-S. Lönnroth et al, ''Predictive transport modelling of type I ELMy H-mode dynamics using a theory-motivated combined ballooning–peeling model'', Plasma Phys. Control. Fusion '''46''' (2004) 1197-1215]&lt;/ref&gt;&lt;ref&gt;[http://dx.doi.org/10.1088/0029-5515/49/9/095015 N. Hayashi et al, ''Integrated simulation of ELM energy loss and cycle in improved H-mode plasmas'', Nucl. Fusion '''49''' (2009) 095015]&lt;/ref&gt;
* Coupled peeling-ballooning modes <ref>[http://link.aip.org/link/?PHPAEN/5/2687/1 J.W. Connor et al, ''Magnetohydrodynamic stability of tokamak edge plasmas'', Phys. Plasmas '''5''' (1998) 2687]</ref><ref>[http://link.aip.org/link/?PHPAEN/9/2037/1 P.B. Snyder et al, ''Edge localized modes and the pedestal: A model based on coupled peeling–ballooning modes'', Phys. Plasmas '''9''' (2002) 2037]</ref><ref>[http://dx.doi.org/10.1088/0741-3335/46/8/003 J.-S. Lönnroth et al, ''Predictive transport modelling of type I ELMy H-mode dynamics using a theory-motivated combined ballooning–peeling model'', Plasma Phys. Control. Fusion '''46''' (2004) 1197-1215]</ref><ref>[http://dx.doi.org/10.1088/0029-5515/49/9/095015 N. Hayashi et al, ''Integrated simulation of ELM energy loss and cycle in improved H-mode plasmas'', Nucl. Fusion '''49''' (2009) 095015]</ref>
* Peeling modes &lt;ref&gt;[http://link.aip.org/link/?APCPCS/871/87/1 C.G. Gimblett, ''Peeling mode relaxation ELM model'', AIP Conf. Proc. '''871''' (2006) 87-99]&lt;/ref&gt;
* Peeling modes <ref>[http://link.aip.org/link/?APCPCS/871/87/1 C.G. Gimblett, ''Peeling mode relaxation ELM model'', AIP Conf. Proc. '''871''' (2006) 87-99]</ref>
* Flux surface peeling &lt;ref&gt;[http://dx.doi.org/10.1016/j.jnucmat.2004.09.067 E.R. Solano et al, ''ELMs and strike point jumps'', Journal of Nuclear Materials '''337-339''' (2005) 747-750 ]&lt;/ref&gt;
* Flux surface peeling <ref>[http://dx.doi.org/10.1016/j.jnucmat.2004.09.067 E.R. Solano et al, ''ELMs and strike point jumps'', Journal of Nuclear Materials '''337-339''' (2005) 747-750 ]</ref>
* [[Criticality of MHD equilibrium]] &lt;ref&gt; [http://dx.doi.org/10.1088/0741-3335/46/3/L02 Emilia R. Solano, ''Criticality of the Grad–Shafranov equation: transport barriers and fragile equilibria'',  Plasma Phys. Control. Fusion '''46''' (2004) L7-L13] &lt;/ref&gt;
* [[Criticality of MHD equilibrium]] <ref> [http://dx.doi.org/10.1088/0741-3335/46/3/L02 Emilia R. Solano, ''Criticality of the Grad–Shafranov equation: transport barriers and fragile equilibria'',  Plasma Phys. Control. Fusion '''46''' (2004) L7-L13] </ref>
* [[Self-Organised Criticality]] &lt;ref&gt;[http://dx.doi.org/10.1088/0029-5515/43/10/003 R. Sánchez et al, ''Modelling of ELM-like phenomena via mixed SOC-diffusive dynamics'', Nucl. Fusion '''43''' (2003) 1031-1039 ]&lt;/ref&gt;
* [[Self-Organised Criticality]] <ref>[http://dx.doi.org/10.1088/0029-5515/43/10/003 R. Sánchez et al, ''Modelling of ELM-like phenomena via mixed SOC-diffusive dynamics'', Nucl. Fusion '''43''' (2003) 1031-1039 ]</ref>


== ELMs and machine operation ==
== ELMs and machine operation ==
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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-modes exist (without ELMs),
Although Quiescent H-modes exist (without ELMs),
&lt;ref&gt;[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]&lt;/ref&gt;
<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>
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.
&lt;ref&gt;[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]&lt;/ref&gt;
<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>


== References ==
== References ==
&lt;references /&gt;
<references />
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