Development of 320CH 2D ion Doppler tomography for the investigation of fine structure measurement of high guide field reconnection

The fine structure of high guide field reconnection has been investigated using a new 96CH/320CH sub-cm 2D ion Doppler tomography diagnostics in TS-6 tokamak merging experiment. In addition to the previously reported ion heating characteristics of double peak profile formation, the new system successfully detects two types of fine structure of high guide field reconnection: (i) localized ion heating in the diffusion region and (ii) field-aligned fine structure formation in the downstream. The former case is affected by Hall effect and forms more tilted profile with higher mass ratio; while in the latter case, high T_i area starts propagating along the closed flux surface formed by reconnected field lines because the ratio of parallel/perpendicular heat diffusivity c^⊥/c^∥~ 2(w_cit_ii)² is higher than 10 even in low field side for tokamak merging. The improvement of transport coefficient with high guide field strongly suppresses the perpendicular heat conduction and the reconnection heating transport finally forms a double-ring-like structure after the end of merging.