Studies on absorption of EC waves in assisted startup experiment on FTU

Abstract

Abstract. Assistance of EC wave for plasma breakdown and current ramp up is the proposed scenario for the ITER case, characterized by low toroidal electric field. The experimental results on many tokamaks clearly indicate the capabilities of the proposed scheme to have a robust breakdown in ITER. The key aspect of this technique is the EC power required, strongly related to the absorption of the wave in the initial stage of plasma formation. This aspect is generally neglected due to the diagnostics difficulties in the plasma formation phase. As a consequence a multi-pass absorption scheme is usually considered reasonable, leading to a strong absorption after many reflections on the walls. The present study exploits the high temporal and spatial resolution of the fast scanning interferometer of FTU together with the measure of residual power obtained by a sniffer probe. The absorbed EC power is calculated considering also the polarization rotation and the subsequent mode conversion after incidence on the internal wall and compared with that derived from experimental data. The resulting EC power distribution can explain differences observed between perpendicular and oblique injection results, indicating future investigations to define ITER power requirements.

Modelling effects of edge density fluctuations on electron-cyclotron current drive used for neoclassical tearing mode stabilization

“…Since the tokamak magnetic field is non-uniform, under specific choices for the beam launching conditions, the EC resonance may be realized in a very narrow spatial region. In this respect, using EC waves gives the advantage of good localization in the power deposition, which is exploited in applications relevant to auxiliary plasma heating (Prater 2004), plasma ramp-up and breakdown assistance (Granucci et al 2012), sawtooth and neoclassical tearing mode (NTM) instability control (LaHaye 2006), as well as plasma diagnostics based on electromagnetic (EM) waves like, for example, reflectometry and interferometry (Hutchinson 2005). From the EC-relevant applications, NTM stabilization is of central interest in this work.…”