TJ-II:Transport and magnetic configuration: Difference between revisions

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A significant part of the research effort at TJ-II is dedicated to the study of the interaction between transport and the (flexible) magnetic configuration.
A significant part of the research effort at [[TJ-II]] is dedicated to the study of the interaction between transport and the (flexible) magnetic configuration.
<ref>[http://dx.doi.org/10.1088/0741-3335/41/12B/307 C. Alejaldre et al, ''Confinement studies in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''41''' (1999) B109]</ref>
<ref>C. Alejaldre et al, ''Confinement studies in the TJ-II stellarator'', [[doi:10.1088/0741-3335/41/12B/307|Plasma Phys. Control. Fusion '''41''' (1999) B109]]</ref>
<ref>[http://dx.doi.org/10.1088/0741-3335/45/3/304 M.A. Ochando et al, ''Emissivity toroidal asymmetries induced by ECRH driven convective fluxes in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''45''' (2003) 221-231]</ref>
<ref>M.A. Ochando et al, ''Emissivity toroidal asymmetries induced by ECRH driven convective fluxes in the TJ-II stellarator'', [[doi:10.1088/0741-3335/45/3/304|Plasma Phys. Control. Fusion '''45''' (2003) 221-231]]</ref>
<ref>[http://dx.doi.org/10.1088/0029-5515/45/10/S22 C. Hidalgo et al, ''Overview of TJ-II experiments'', Nucl. Fusion '''45''' (2005) S266-S275]</ref>
<ref>C. Hidalgo et al, ''Overview of TJ-II experiments'', [[doi:10.1088/0029-5515/45/10/S22|Nucl. Fusion '''45''' (2005) S266-S275]]</ref>
<ref>[http://dx.doi.org/10.1088/0029-5515/45/4/009 E. Ascasíbar et al, ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion '''45''' (2005) 276-284]</ref>
The following issues contribute to the influence of the configuration on confinement:
The following issues contribute to the influence of the configuration on confinement:
* Rational surfaces (the iota profile) <ref>[http://dx.doi.org/10.1088/0029-5515/44/5/008 D. López-Bruna et al, ''Effects of ohmic current in the TJ-II stellarator'', Nucl. Fusion '''44''', 5 (2004) 645-654]</ref> <ref>[http://dx.doi.org/10.1209/0295-5075/82/65002 D. López-Bruna et al, ''Tracking magnetic resonances in the effective electron heat diffusivity of ECH plasmas of the TJ-II Heliac'', EuroPhysics Letters '''82''' (2008) 65002]</ref>
* The [[rotational transform]] <ref>E. Ascasíbar et al, ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', [[doi:10.1088/0029-5515/45/4/009|Nucl. Fusion '''45''' (2005) 276-284]]</ref>
* [[Magnetic shear]]
* Rational surfaces <ref>D. López-Bruna et al, ''Tracking magnetic resonances in the effective electron heat diffusivity of ECH plasmas of the TJ-II Heliac'', [[doi:10.1209/0295-5075/82/65002|EuroPhysics Letters '''82''' (2008) 65002]]</ref><ref>D. López-Bruna et al, ''First dynamic magnetic configuration scans in ECRH plasmas of the TJ-II Heliac'', [[doi:10.1088/0029-5515/49/8/085016|Nucl. Fusion '''49''' (2009) 085016]]</ref><ref>D. López-Bruna et al, ''Magnetic Resonances in ECR-Heated Plasmas of the TJ-II Heliac'', [[doi:10.1002/ctpp.200900005|Contrib. Plasma Phys. '''50''' (2010) 600]]</ref><ref>D. López-Bruna et al, ''Magnetic resonances and electric fields in the TJ-II Heliac'', [[doi:10.1088/0741-3335/53/12/124022|Plasma Phys. Control. Fusion 53 (2011) 124022]]</ref><ref>D. López-Bruna et al, ''Relationship between MHD events, magnetic resonances and transport barriers in TJ-II plasmas'', [[doi:10.1088/0029-5515/53/7/073051|Nucl. Fusion '''53''', 7 (2013) 073051]]</ref>
* [[Magnetic well]] <ref>[http://dx.doi.org/10.1088/0741-3335/43/12A/324 C. Hidalgo et al, ''On the radial scale of fluctuations in the TJ-II stellarator'', Plasma Phys. Control. Fusion '''43''' (2001) A313-A321]</ref> <ref>[http://link.aip.org/link/?PHPAEN/9/713/1 J. Castellano et al, ''Magnetic well and instability thresholds in the TJ-II stellarator'', Phys. Plasmas '''9''' (2002) 713]</ref> <ref>[http://dx.doi.org/10.1088/0741-3335/44/12B/322 E. Ascasíbar et al, ''Confinement and stability on the TJ-II stellarator'', Plasma Phys. Control. Fusion '''44''' (2002) B307-B322]</ref>
* [[Magnetic shear]] <ref>J.A. Romero et al, ''Controlling confinement with induced toroidal current in the flexible Heliac TJ-II'', [[doi:10.1088/0029-5515/43/6/301|Nucl. Fusion '''43''' (2003) 387-392]]</ref> <ref>D. López-Bruna et al, ''Effects of ohmic current in the TJ-II stellarator'', [[doi:10.1088/0029-5515/44/5/008|Nucl. Fusion '''44''', 5 (2004) 645-654]]</ref>
* [[Magnetic well]] <ref>C. Hidalgo et al, ''On the radial scale of fluctuations in the TJ-II stellarator'', [[doi:10.1088/0741-3335/43/12A/324|Plasma Phys. Control. Fusion '''43''' (2001) A313-A321]]</ref> <ref>J. Castellano et al, ''Magnetic well and instability thresholds in the TJ-II stellarator'', [[doi:10.1063/1.1430435|Phys. Plasmas '''9''' (2002) 713]]</ref> <ref>E. Ascasíbar et al, ''Confinement and stability on the TJ-II stellarator'', [[doi:10.1088/0741-3335/44/12B/322|Plasma Phys. Control. Fusion '''44''' (2002) B307-B322]]</ref>


The picture emerging from these studies is complex. In general, the presence of low-order rational surfaces in the plasma does not seem to be deleterious for transport; rather, local reductions of transport are observed (except at very low shear). Possibly, this is associated with the formation of [[TJ-II:Internal Transport Barriers|internal transport barriers]] at or near such rational surfaces, a consequence of the modification of the radial electric field by the rational surfaces themselves. It is being investigated whether the plasmas where this has been studied have the conditions for a self-healing state of the corresponding magnetic perturbations. On the other hand, the reduction of the magnetic well clearly enhances turbulence levels.


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

Latest revision as of 11:05, 25 November 2014

A significant part of the research effort at TJ-II is dedicated to the study of the interaction between transport and the (flexible) magnetic configuration. [1] [2] [3] The following issues contribute to the influence of the configuration on confinement:

The picture emerging from these studies is complex. In general, the presence of low-order rational surfaces in the plasma does not seem to be deleterious for transport; rather, local reductions of transport are observed (except at very low shear). Possibly, this is associated with the formation of internal transport barriers at or near such rational surfaces, a consequence of the modification of the radial electric field by the rational surfaces themselves. It is being investigated whether the plasmas where this has been studied have the conditions for a self-healing state of the corresponding magnetic perturbations. On the other hand, the reduction of the magnetic well clearly enhances turbulence levels.

References

  1. ↑ C. Alejaldre et al, Confinement studies in the TJ-II stellarator, Plasma Phys. Control. Fusion 41 (1999) B109
  2. ↑ M.A. Ochando et al, Emissivity toroidal asymmetries induced by ECRH driven convective fluxes in the TJ-II stellarator, Plasma Phys. Control. Fusion 45 (2003) 221-231
  3. ↑ C. Hidalgo et al, Overview of TJ-II experiments, Nucl. Fusion 45 (2005) S266-S275
  4. ↑ E. Ascasíbar et al, Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator, Nucl. Fusion 45 (2005) 276-284
  5. ↑ D. López-Bruna et al, Tracking magnetic resonances in the effective electron heat diffusivity of ECH plasmas of the TJ-II Heliac, EuroPhysics Letters 82 (2008) 65002
  6. ↑ D. López-Bruna et al, First dynamic magnetic configuration scans in ECRH plasmas of the TJ-II Heliac, Nucl. Fusion 49 (2009) 085016
  7. ↑ D. López-Bruna et al, Magnetic Resonances in ECR-Heated Plasmas of the TJ-II Heliac, Contrib. Plasma Phys. 50 (2010) 600
  8. ↑ D. López-Bruna et al, Magnetic resonances and electric fields in the TJ-II Heliac, Plasma Phys. Control. Fusion 53 (2011) 124022
  9. ↑ D. López-Bruna et al, Relationship between MHD events, magnetic resonances and transport barriers in TJ-II plasmas, Nucl. Fusion 53, 7 (2013) 073051
  10. ↑ J.A. Romero et al, Controlling confinement with induced toroidal current in the flexible Heliac TJ-II, Nucl. Fusion 43 (2003) 387-392
  11. ↑ D. López-Bruna et al, Effects of ohmic current in the TJ-II stellarator, Nucl. Fusion 44, 5 (2004) 645-654
  12. ↑ C. Hidalgo et al, On the radial scale of fluctuations in the TJ-II stellarator, Plasma Phys. Control. Fusion 43 (2001) A313-A321
  13. ↑ J. Castellano et al, Magnetic well and instability thresholds in the TJ-II stellarator, Phys. Plasmas 9 (2002) 713
  14. ↑ E. Ascasíbar et al, Confinement and stability on the TJ-II stellarator, Plasma Phys. Control. Fusion 44 (2002) B307-B322
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