Dynamic characteristics of edge plasma profiles during the opening of edge islands on the J-TEXT tokamak

Abstract

Abstract On the J-TEXT tokamak, the dynamics of edge magnetic topology during the opening of the edge magnetic islands induced by the external Resonant Magnetic Perturbation (RMP) are investigated. The edge island chain is pushed outward by increasing plasma toroidal current to intersect the poloidally and toroidally localized divertor plate, forming an open magnetic island in the Scrape-Off Layer (SOL). The location of the strike points on the divertor plate predicted by the HINT code is in agreement with the experimental observations. The influence of the magnetic topology on edge plasma profiles has also been investigated using Langmuir probes. The properties of edge T e , n e , P e and E r profiles are studied as function of three magnetic structures in q a -dependence experiments and two magnetic structures in RMP configuration-dependence experiments. Some common features are observed. Inside the edge closed and SOL remnant islands, flat P e but non-flat T e and n e profiles are detected. When transitioning from the edge closed island to the partially open island with remnant island, the local flat P e profile is shifted outward accompanied by a narrower flattened P e region. The steep slopes of T e , n e and P e are measured in the SOL regions characterized by a long connection length L c , and the longer L c , the steeper slopes. E r exhibits a negative well inside the remnant island with infinite L c and in the SOL regions where L c significantly exceeds than the electron mean free path λ e , but develops a positive value in the SOL regions where L c is relatively short.