Formation of the non-axisymmetric helical current driven by a biased electrode in the scrape-off layer on J-TEXT

摘要

Resonant magnetic perturbations (RMPs), which change the magnetic topology, have been applied to control the edge-localized modes (ELMs) in many tokamak experiments. The non-axisymmetric helical currents induced by lower hybrid waves in the scrape-off layer (SOL) were observed to impact the magnetic topology profoundly and mitigated ELMs strongly in EAST (Liang et al 2013 Phys. Rev. Lett. 110 235002). In this paper, we present electrode biasing in the SOL as an alternative method to drive the non-axisymmetric helical currents in J-TEXT. A significant SOL current (e.g. similar to 150 A) was induced through the electrode with a biasing voltage of -200 V. The measured magnetic fields perturbed by the biasing current are consistent with those calculated from the helical currents flowing along the opened magnetic field lines in the SOL. This consistency reveals that the biased electrode induced non- axisymmetric helical currents in the SOL. The 3/1 component of the RMP field generated by the non-axisymmetric helical current can reach 13 Gauss kA(-1) at the last closed flux surface. This indicates that the non-axisymmetric helical currents driven by biasing in the SOL might be an attractive new method for producing an RMP field and hence for controlling plasma instabilities such as ELMs.