Lower hybrid current drive in the Tore Supra tokamak

Licentiatavhandling, 2014

To control and extract energy from nuclear fusion reactions, a mixture of deuterium and tritium gases must be heated to temperatures on the order of 100 million degrees, whilst maintaining a sufficiently high density. The main difficulty is to confine the ionised gases, i.e. plasma, until the rate of fusion reactions becomes large enough. In the most promising type of magnetic confinement fusion device, known as tokamak, steady state operation is highly desirable and can only be reached by non-inductive current drive methods, to complement the confining magnetic field. The best, experimentally proven method is by injection of lower hybrid (LH) waves that transfer momentum to the electrons in the plasma. In the Tore Supra tokamak, LH waves at a frequency of 3.7 GHz are coupled to the plasma for current drive using a fully active multijunction (FAM) launcher and/or a passive active multijunction (PAM) launcher, which was installed recently to test an antenna design relevant for ITER, which is the next large-scale tokamak currently under con- struction. In this thesis a study of fully non-inductive discharges with either the FAM or PAM launchers is performed, using a suite of codes specifically developed for LH current drive. Good agreement is found between experiments and simulations for such discharges at relatively low density. A detailed comparison of the LH power deposition profile and current drive efficiency with the two launchers is made. The par- allel refractive index spectra (n∥) of the two launchers are found to be noticeably different, resulting in different current profiles.