TJ-II:Transport and magnetic configuration

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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. [1] [2] [3] The following issues contribute to the influence of the configuration on confinement:

  • The rotational transform [4]
  • Rational surfaces [5]

[6] [7]

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, Tracking magnetic resonances in the effective electron heat diffusivity of ECH plasmas of the TJ-II Heliac, EuroPhysics Letters 82 (2008) 65002
  8. ↑ J.A. Romero et al, Controlling confinement with induced toroidal current in the flexible Heliac TJ-II, Nucl. Fusion 43 (2003) 387-392
  9. ↑ D. López-Bruna et al, Effects of ohmic current in the TJ-II stellarator, Nucl. Fusion 44, 5 (2004) 645-654
  10. ↑ C. Hidalgo et al, On the radial scale of fluctuations in the TJ-II stellarator, Plasma Phys. Control. Fusion 43 (2001) A313-A321
  11. ↑ J. Castellano et al, Magnetic well and instability thresholds in the TJ-II stellarator, Phys. Plasmas 9 (2002) 713
  12. ↑ E. Ascasíbar et al, Confinement and stability on the TJ-II stellarator, Plasma Phys. Control. Fusion 44 (2002) B307-B322
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