Increasing NTM Stabilization Efficiency Using Modulated ECCD In ASDEX Upgrade

摘要

This paper reports on the experimental studies, performed in the tokamak ASDEX Upgrade, for increasing the efficiency in generating a helical current within magnetic islands with the purpose of suppressing neoclassical tearing modes (NTMs) by electron cyclotron current drive (ECCD). It is shown that the efficiency of generating this current by continuous CD in a rotating island drops drastically as the width 2d of the co-ECCD driven current becomes larger than the islands size W. However, by modulating the co-ECCD in phase with the island's O-point, the efficiency is recovered. The results are in good agreement with theoretical calculations taking into account the equilibration of the externally driven current on the island flux surfaces. The result is especially important for large next-step fusion devices, such as ITER, where 2d>W is expected to be unavoidable during NTM suppression, indicating that modulation capability should be foreseen.