MHD Islands Tracking via Oblique ECE

The paper aims to assess the concept of a control loop using only the Electron Cyclotron Emission (ECE) diagnostics for the identification and tracking of the Neoclassical Tearing Mode (NTM) instability. In particular, the so-called quasi-in-line (QI) ECE configuration has been considered which is a layout where the viewing line of sight is quasi-collinear with respect to the Electron Cyclotron Current Drive (ECCD) actuator aiming to the unstable island to perform its suppression or control. The QI-ECE configuration is shown to be sensitive enough and offers an alignment technique largely independent from the magnetic reconstruction and from the calculation of the EC refraction effects. This seems particularly attractive for a fusion reactor environment where magnetic measurements and the equilibrium reconstruction may be affected by significant uncertainties.