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  • Role of the current density profile on drift wave stability in internal transport barrier reversed magnetic shear experiments at JET and Tore Supra


The role of the current density profile on drift wave stability is investigated using a linear electrostatic gyro-kinetic code. The growth rates are shown to have a linear dependence on the normalized temperature gradients above a certain threshold. A parametric study of the threshold shows a dramatic stabilizing effect of negative magnetic shear, especially for large scale instabilities. A set of handy formulae fitting the threshold as a function of the magnetic shear and the safety factor is proposed.

Analysis of reversed magnetic shear discharges with internal transport barrier (ITB) in JET shows that ion ITBs can be triggered by the negative magnetic shear in the core of the plasma. Subsequently, the increase of the E×B shearing rate allows for the expansion of the ITB, despite the increase of the linear growth rates due to the temperature gradient peaking. In the case of the electron ITB obtained in the Tore Supra LHEP mode, the central increase of the confinement is associated with the stabilization of large scale trapped electron modes by the negative magnetic shear effect, whereas the steep electron temperature gradient destabilizes the small scale electron temperature gradient modes, which prevent the electron heat transport to reach neoclassical levels.

Additional information

Authors: FOURMENT C ET AL, EURATOM-CEA Association, CEA/DSM/DRFC, CEA Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion 45 (March 2003) pp.233-250
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at:
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