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TJ-II:Confinement transitions (view source)

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While this phenomenon is still not completely understood, much progress has been made in recent years. It is believed that turbulent fluctuations drive sheared or zonal flows via the [[Reynolds stress|Reynolds Stress Mechanism]].  
While this phenomenon is still not completely understood, much progress has been made in recent years. It is believed that turbulent fluctuations drive sheared or zonal flows via the [[Reynolds stress|Reynolds Stress Mechanism]].  
<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>
<ref>[[doi: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>
This mechanism transfers energy of high-frequency drift type turbulence to low wavelength modes. The zonal flow itself is radially localized and has a very long (infinite) toroidal and poloidal wavelength. This flow then shears the turbulent eddies apart, leading to local turbulence suppression at specific radial locations, and a concomitant local reduction of transport.
This mechanism transfers energy of high-frequency drift type turbulence to low wavelength modes. The zonal flow itself is radially localized and has a very long (infinite) toroidal and poloidal wavelength. This flow then shears the turbulent eddies apart, leading to local turbulence suppression at specific radial locations, and a concomitant local reduction of transport.
<ref>[http://dx.doi.org/10.1088/0741-3335/47/5/R01 P.H. Diamond et al, ''Zonal flows in plasma - a review'', Plasma Phys. Control. Fusion '''47''' (2005) R35-R161]</ref>
<ref>[[doi:10.1088/0741-3335/47/5/R01|P.H. Diamond et al, ''Zonal flows in plasma - a review'', Plasma Phys. Control. Fusion '''47''' (2005) R35-R161]]</ref>


At [[TJ-II]], much effort has been invested in the experimental measurement and theoretical understanding of this phenomenon.
At [[TJ-II]], much effort has been invested in the experimental measurement and theoretical understanding of this phenomenon.
<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.84.4842 P.H. Diamond et al, ''In search of the elusive zonal flow using cross-bicoherence analysis'', Phys. Rev. Lett. '''84''', 12 (2000) 4842]</ref>
<ref>[[doi:10.1103/PhysRevLett.84.4842|P.H. Diamond et al, ''In search of the elusive zonal flow using cross-bicoherence analysis'', Phys. Rev. Lett. '''84''', 12 (2000) 4842]]</ref>
<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.91.065001 C. Hidalgo et al, ''Experimental Investigation of Dynamical Coupling between Turbulent Transport and Parallel Flows in the JET Plasma-Boundary Region'', Phys. Rev. Lett. '''91''' (2003) 065001]</ref>
<ref>[[doi:10.1103/PhysRevLett.91.065001|C. Hidalgo et al, ''Experimental Investigation of Dynamical Coupling between Turbulent Transport and Parallel Flows in the JET Plasma-Boundary Region'', Phys. Rev. Lett. '''91''' (2003) 065001]]</ref>
<ref>[http://link.aps.org/doi/10.1103/PhysRevE.70.067402 C. Hidalgo et al., ''Experimental evidence of coupling between sheared-flow development and an increase in the level of turbulence in the TJ-II stellarator'', Phys. Rev. E '''70''' (2004) 067402]</ref>
<ref>[[doi:10.1103/PhysRevE.70.067402|C. Hidalgo et al., ''Experimental evidence of coupling between sheared-flow development and an increase in the level of turbulence in the TJ-II stellarator'', Phys. Rev. E '''70''' (2004) 067402]]</ref>
<ref>[http://dx.doi.org/10.1088/0741-3335/46/1/018 C. Hidalgo et al, ''Improved confinement regimes induced by limiter biasing in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''46''' (2004) 287-297]</ref>
<ref>[[doi:10.1088/0741-3335/46/1/018|C. Hidalgo et al, ''Improved confinement regimes induced by limiter biasing in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''46''' (2004) 287-297]]</ref>
<ref>[http://dx.doi.org/10.1088/0741-3335/47/6/004 M.A. Pedrosa et al., ''Threshold for sheared flow and turbulence development in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''47''' (2005) 777-788 ]</ref>
<ref>[[doi:10.1088/0741-3335/47/6/004|M.A. Pedrosa et al., ''Threshold for sheared flow and turbulence development in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''47''' (2005) 777-788]]</ref>
<ref>[http://dx.doi.org/10.1016/j.jnucmat.2004.10.067 E. Sánchez et al., ''On the energy transfer between flows and turbulence in the plasma boundary of fusion devices'', J. of Nuclear Materials '''337''' (2005) 296]</ref>
<ref>[[doi:10.1016/j.jnucmat.2004.10.067|E. Sánchez et al., ''On the energy transfer between flows and turbulence in the plasma boundary of fusion devices'', J. of Nuclear Materials '''337''' (2005) 296]]</ref>
<ref>[http://link.aip.org/link/?PHPAEN/13/122509/1 B.A. Carreras et al, ''Critical transition for the edge shear layer formation: Comparison of model and experiment'', Phys. Plasmas '''13''' (2006) 122509]</ref>
<ref>[[doi:10.1063/1.2405344|B.A. Carreras et al, ''Critical transition for the edge shear layer formation: Comparison of model and experiment'', Phys. Plasmas '''13''' (2006) 122509]]</ref>
<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.96.145001 B. Gonçalves et al., ''Role of Turbulence on Edge Momentum Redistribution in the TJ-II Stellarator'', Phys. Rev. Lett. '''96''' (2006) 145001]</ref>
<ref>[[doi:10.1103/PhysRevLett.96.145001|B. Gonçalves et al., ''Role of Turbulence on Edge Momentum Redistribution in the TJ-II Stellarator'', Phys. Rev. Lett. '''96''' (2006) 145001]]</ref>
<ref>[http://dx.doi.org/10.1088/0029-5515/48/11/115003 B.Ph. van Milligen et al, ''Bicoherence during confinement transitions in the TJ-II stellarator'', Nucl. Fusion '''48''' (2008) 115003]</ref>
<ref>[[doi:10.1088/0029-5515/48/11/115003|B.Ph. van Milligen et al, ''Bicoherence during confinement transitions in the TJ-II stellarator'', Nucl. Fusion '''48''' (2008) 115003]]</ref>
<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.100.215003 M.A. Pedrosa et al, ''Evidence of Long-Distance Correlation of Fluctuations during Edge Transitions to Improved-Confinement Regimes in the TJ-II Stellarator'', Phys. Rev. Lett. '''100''' (2008) 215003]</ref>
<ref>[[doi:10.1103/PhysRevLett.100.215003|M.A. Pedrosa et al, ''Evidence of Long-Distance Correlation of Fluctuations during Edge Transitions to Improved-Confinement Regimes in the TJ-II Stellarator'', Phys. Rev. Lett. '''100''' (2008) 215003]]</ref>
<ref>[http://dx.doi.org/10.1088/0741-3335/51/6/065007 I. Calvo et al, ''Zonal flows and long-distance correlations during the formation of the edge shear layer in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''51''' (2009) 065007]</ref>
<ref>[[doi:10.1088/0741-3335/51/6/065007|I. Calvo et al, ''Zonal flows and long-distance correlations during the formation of the edge shear layer in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''51''' (2009) 065007]]</ref>
<ref>[http://dx.doi.org/10.1209/0295-5075/87/55002 C. Hidalgo et al, ''Multi-scale physics mechanisms and spontaneous edge transport  bifurcations in fusion plasmas'', Europhys. Lett. '''87''' (2009) 55002]</ref>
<ref>[[doi:10.1209/0295-5075/87/55002|C. Hidalgo et al, ''Multi-scale physics mechanisms and spontaneous edge transport  bifurcations in fusion plasmas'', Europhys. Lett. '''87''' (2009) 55002]]</ref>
<ref>[http://dx.doi.org/10.1088/0741-3335/51/12/124015 T. Estrada et al, ''Sheared flows and transition to improved confinement regime in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''51''' (2009) 124015]</ref>
<ref>[[doi:10.1088/0741-3335/51/12/124015|T. Estrada et al, ''Sheared flows and transition to improved confinement regime in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''51''' (2009) 124015]]</ref>
<ref>[[doi:10.1088/0029-5515/51/11/113002|B.Ph. van Milligen et al, ''The dynamics of the formation of the edge particle transport barrier at TJ-II'', Nucl. Fusion '''51''' (2011) 113002]]</ref>


== References ==
== References ==
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<references />
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