Abstract

The injection of radiofrequency waves in a tokamak plasma to drive the toroidal current serves a double purpose. First, the non inductive nature of the method allows to avoid the variable currents circulating in the coils, hardly compatible with the steady-state operation of a future reactor. Moreover, it is widely recognized that the plasma performances are mainly limited by magnetic turbulence. However, this turbulence can be reduced, and even suppressed when the current profile is optimized, which is possible through the use of waves, in the framework of advanced scenarios.

In this thesis, the use of electron cyclotron waves (EC) to control the current profile is investigated. A first issue is the polarization of the waves in hot plasmas, since it is known to determine the quality of the wave-plasma interaction. The finite temperature effects on the polarization are thus studied in various regimes. On the other hand, in advanced scenarios, the association of EC and lower hybrid (LH) is promising because of their complementary features. A large part of this work is thus devoted to the theoretical, numerical and experimental study of combined discharges.

The obtained results, among which the analytical demonstration of a synergy effect between the two waves, clearly show the advantages of this kind of scenario and trigger the development of new experiments.