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Electron Internal Transport Barriers and Magnetic Topology in the Stellarator TJ-II

T. Estrada, D. López-Bruna, A. Alonso, E. Ascasíbar, A. Baciero, A. Cappa, F. Castejón, A. Fernández, J. Herranz, C. Hidalgo, J. L. De Pablos, I. Pastor, E. Sánchez, J. Sánchez, L. Krupnik, A. A. Chmyga, N. Dreval, S. M. Khrebtov, A. D. Komarov, A. S. Kozachok, V. Tereshin, A. V. Melnikov, L. Eliseev

Fusion Science and Technology / Volume 50 / Number 2 / August 2006 / Pages 127-135

Technical Paper / Stellarators /

In most helical systems, electron-internal transport barriers (e-ITBs) are observed in electron cyclotron heated (ECH) plasmas with high heating power density. In the stellarator TJ-II, e-ITBs are easily achievable by positioning a low-order rational surface close to the plasma core because this increases the density range in which the e-ITB can form. Experiments with different low-order rationals show a dependence of the threshold density and barrier quality on the order of the rational (3/2, 4/2, 5/3 . . .). In addition, quasi-coherent modes are frequently observed before and/or after the e-ITB phenomenon at the radial location of the transport barrier foot. Such modes vanish as the barrier is fully developed.

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