Abstract
Lower hybrid enhanced performance (LHEP) discharges have been
successfully operated on Tore Supra, with a significant improvement in
electron core-confinement and remarkable steady-state features. However,
recent attempts to operate such discharges with better confinement
performance were hindered by the systematic onset of large MHD activity,
preventing any good performance recovery. The associated MHD limit is
found to result from reaching the tearing mode limit as the current
profile is driven from centrally peaked towards off-axis peaked by the
lower hybrid (LH) wave. The specific feature of the considered
discharges is that they achieve a weak magnetic shear over a broader
core region than past LHEP discharges, then leading to systematic fast
MHD onset (m/n = 2/1 tearing mode) when qmin approaches 2.
The present paper reports on experimental observations and modelling
which support this finding and analyses the perspectives of improving
the LHEP scenario by combining the current profile control through the
LH wave with a significant increase in pressure through ion cyclotron
wave coupling.
Original language | English |
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Pages (from-to) | 1625-1639 |
Journal | Plasma Physics and Controlled Fusion |
Volume | 43 |
Issue number | 12 |
DOIs | |
Publication status | Published - 1 Dec 2001 |
Externally published | Yes |