Study of divertor heat flux widths in type-I ELMy H-mode with infra-red thermography on EAST tokamak

Abstract

Characteristic widths of divertor power load footprints, i.e., power decay length λq, Gaussian dissipation width S and integral power width λint in radio-frequency (RF) heated type-I ELMy H-modes are investigated with infra-red (IR) thermography diagnostic on experimental advanced superconducting tokamak (EAST). The fitting of divertor heat flux profile to Eich function is employed to obtain λq and S [2]. The heat flux widths on lower-outer (LO) divertor plates are found larger than those of lower-inner (LI) plates, and obvious multi-peak structures are found on LO divertor power load footprints. A comparison of LI heat flux widths of ELM-averaged in type-I ELMy H-mode to those within inter-ELM phases indicates that the widths are similar, in magnitude, for the two cases. The λq mapping to the outer mid-plane (OMP) from the LI divertor has a strong inverse dependence on Ip (or equivalently poloidal magnetic field at the OMP, Bp,omp) in the form of λqEAST,type−I=(2.45±0.3)×Ip−1.01±0.11 (or λqEAST,type−I=(0.64±0.17)×Bp,omp−1.25±0.14), which is in satisfactory agreement, in tendency, with the multi-machine experimental scaling results and heuristic drift-based model proposed by Goldston. In addition, the linear regression of ELM-averaged S, on LI divertor during type-I ELMy H-mode, with Ip shows a decrease tendency, being consistent with the case of LO target in EAST type-III ELMy H-mode. This work may provide useful information for the extrapolation to ITER, whose baseline operation scenario is type-I ELMy H-mode.