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

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 <?CDATA Tₑ?> T e , <?CDATA nₑ?> n e , <?CDATA Pₑ?> P e and <?CDATA Eᵣ?> E r profiles are studied as function of three magnetic structures in <?CDATA qₐ?> 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 <?CDATA Pₑ?> P e but non-flat <?CDATA Tₑ?> T e and <?CDATA nₑ?> n e profiles are detected. When transitioning from the edge closed island to the partially open island with remnant island, the local flat <?CDATA Pₑ?> P e profile is shifted outward accompanied by a narrower flattened <?CDATA Pₑ?> P e region. The steep slopes of <?CDATA Tₑ?> T e , <?CDATA nₑ?> n e and <?CDATA Pₑ?> P e are measured in the SOL regions characterized by a long connection length <?CDATA Lc?> L c , and the longer <?CDATA Lc?> L c , the steeper slopes. <?CDATA Eᵣ?> E r exhibits a negative well inside the remnant island with infinite <?CDATA Lc?> L c and in the SOL regions where <?CDATA Lc?> L c significantly exceeds than the electron mean free path <?CDATA λ ₑ?> λ e , but develops a positive value in the SOL regions where <?CDATA Lc?> L c is relatively short.