Lower Hybrid Current Drive for
the Steady State Scenario
M. Goniche, Y. Baranov, V. Basiuk, G. Calabro, A. Cardinali, C. Castaldo, R.
Cesario, J. Decker, D. Dodt, A. Ekedahl, L. Figini, J. Garcia, G. Giruzzi, J. Hillairet, G.T.
Hoang, A. Hubbard, E. Joffrin, K. Kirov, X. Litaudon, J. Mailloux, T. Oosako, R. Parker,
V. Pericoli Ridolfini, Y. Peysson, P. Platania, F. Rimini, P.K. Sharma,
C. Sozzi, G.Wallace and JET EFDA contributors
Lower Hybrid Current Drive (LHCD) experiments performed at density close to that
required for the steady state scenario are reported. On C-Mod, FTU and Tore Supra, a strong decay of
the brehmsstrahlung emission is observed when the density is increased, much faster that
the prediction of LHCD modelling. On JET, LH power deposition is also found to be sensitive to
the plasma density: LH power modulation indicates that the power deposition moves to the
very edge of the plasma (r/a~0.9) when the density approaches the requirement of the JET SS
scenario. From this experiment but also from the reconstruction of the electron cyclotron emission
spectrum, the decrease of the LHCD efficiency with density is also found. From LHCD modelling
of different JET pulses performed at different densities and wave parallel refraction indexes, it
is concluded that the wave accessibility condition is not the key parameter for explaining the
decrease of the efficiency. C-Mod, FTU and Tore Supra experiments indicate that the plasma
edge parameters, namely density and temperature but also fluctuations, are affecting the
efficiency via loss mechanisms which are likely to be collisional damping (C-Mod), parametric
decay instabilities or wave scattering (FTU/Tore Supra).
Preprint of Paper to be submitted for publication in Proceedings of the
37th EPS Conference on Plasma Physics, Dublin, Ireland.
(21st June 2010 - 25th June 2010)