Formation of a three-dimensional scrape-off layer in a fast rotating resonant magnetic perturbation field at TEXTOR

Abstract

Measurements of electron density ne(r,t) and temperature Te(r,t) fields in the far edge (r/a>0.98) of the tokamak TEXTOR during application of a fast rotating resonant magnetic perturbations (RMP) show an in-phase modulation of both ne and Te coherent to the rotation frequency of the external RMP field, which is correlated to the local rotating magnetic topology. The comparison provides experimental evidence that a three-dimensional scrape-off layer is preserved for high RMP field rotation frequencies of νRMP=974Hz. Additionally, we obtain the geometrical dimensions of the 3D helical flux tubes in terms of the helical and radial width and compare them to the magnetic topology modeled in vacuum approximation in a quasi-static approach. The geometrical dimensions of the experimentally detected flux tubes increase linearly with increasing perturbation current as prescribed by the magnetic topology. For high RMP amplitudes the pressure drop inside the helical flux tube is limited by an effectively enhanced radial transport.