Experimental results of H-mode power threshold with lower hybrid wave heating on the EAST tokamak

摘要

The density roll-over dependence on H-mode power threshold is observed on EAST for the first time. In campaign 2014 and 2015 shots with a toroidal field of 2.25 T have observed rollover dependence with lower hybrid wave as the only auxiliary heating method, while shots with a toroidal field of 1.79 T and 1.9 T exhibit linear dependence consistent with scaling law. The density of minimum power for accessing H-mode on EAST has different plasma current values of 400 kA and 500 kA, and is better described in the normalized Greenwald fraction (n) over cap (G) approximate to 0.4 at B-T = 2.35 T. The absence of (n) over cap (e,min) in 1.7 T and 1.8 T may be attributed to the positive dependence with toroidal field. Besides, correlation analysis of H-mode power threshold and divertor geometry in scanning X-point is summarized and compared. Outer leg length (distance from X-point to outer strike point) has the highest correlation coefficient with H-mode power threshold, which explains the data scattering within the same plasma parameters. A new equation of scaling law is proposed: P-th_EAST = 4.27OLL(1.4) x P-th_08 Neutral particles are believed to be the hidden factor in different divertor geometry, and play a negative role in L-H transition via charge exchange damping.