Tearing Mode Stabilization in Tokamaks with Lower Hybrid Waves

The possibility of using lower hybrid (LH) waves as a source of localized current for the control of MHD instabilities is investigated. A toroidal ray tracing code is used to define the requirements on the launched wave spectrum, in order to drive currents mostly localized inside the magnetic islands. Issues such as the radial diffusion of the non-inductive current, the impact of the radial profile of the power deposition on the stabilization process, the finite time response of the current to RF power modulations and its interplay with the island rotation are addressed by means of a three dimensional (3-D) Fokker–Planck code. It is shown that lower hybrid current drive (LHCD) is a viable option for the control of m = 2 tearing modes in present medium to large tokamaks: the method would be particularly effective in a reactor size machine.