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Recent Lower Hybrid Current Drive (LHCD) experiments in Tore Supra and JET are reported. Large multijunction launchers have allowed the coupling of 5 MW to the plasma for several seconds with a maximum of 3.8 kW/cm2. Measurements of the scattering matrices of the antennae show good agreement with theory. The current drive efficiency in Tore Supra is about 0.2 x 1.0 E20/Am2/W with LH power alone, and reaches 0.4 x 1.0 E20/Am2/W in JET thanks to a high volume-averaged electron temperature (1.9 keV) and also to a synergy between lower hybrid and fast magnetosonic waves. In Tore Supra, sawteeth are suppressed and m=1 MHD oscillations (the frequency of which clearly depends on the amount of LH power) are observed on soft X-rays, and also on non-thermal ECE. In JET, ICRH produced sawtooth-free periods are extended by the application of LHCD (2.9 s with 4 MW ICRH) and current profile broadening has been clearly observed, consistent with off-axis fast electron populations. LH power modulation experiments performed in Tore Supra show a delayed central electron heating despite the off-axis creation of suprathermal electrons, thus ruling out the possibility of a direct heating through central wave absorption. Finally, successful pellet fuelling of a partially LH driven plasma was obtained in Tore Supra, 28 successive pellets allowing the density to rise to 4 x 1.0 E19/m3. This could be achieved by switching the LH power off for 90 ms before each pellet injection, i.e. without modifying significantly the current density profile.

Additional information

Authors: MOREAU D, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR);TORE SUPRA TEAM, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR);GORMEZANO C, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Article: 18th European Conference on Controlled Fusion and Plasma Physics (1991)
Record Number: 199111415 / Last updated on: 1994-12-02
Original language: en
Available languages: en