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In recent experiments in the TCV tokamak, improved energy confinement in the plasma core has been obtained using electron cyclotron current drive (ECCD). A broad electron internal transport barrier (eITB) is observed in the fully sustained ECCD driven non-inductive discharges with off-axis power deposition. For these discharges, the bootstrap fraction is up to 80 substantial off-axis bootstrap current density creates and maintains the reverse shear and therefore the eITB. The steady-state nature of these scenarios and of the barrier location dispels concerns about possible bootstrap / eITB misalignments. The more the q profile is reversed, the stronger the ITB is and the higher energy confinement time. This is demonstrated by adding a small counter CD contribution in the centre, leading to better performances. However an excessive reverse shear can lead to an overly steep pressure gradient at the eITB, triggering MHD activity. By controlling the amount of counter-CD, stable steady-state scenarios are obtained. The properties of the electron temperature barrier and its relation to the degree of reverse shear in the centre will be discussed.

Additional information

Authors: CONDREA I ET AL, Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (CH)
Bibliographic Reference: An oral report given at: 44th Anual Meeting of the Division of Plasma Physics (APS) Organised by: American Physical Society Held at: Orlando, Florida (USA), November 11-15 2002
Availability: Available free of charge from: École Polytechnique Fédérale de Lausanne (EPFL), Ecublens, CH-1015 Lausanne Fax +41-21-6934747
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