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. <ref>C. Alejaldre et al, Confinement studies in the TJ-II stellarator, Plasma Phys. Control. Fusion 41 (1999) B109</ref> <ref>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>C. Hidalgo et al, Overview of TJ-II experiments, Nucl. Fusion 45 (2005) S266-S275</ref> 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.


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