H-mode power threshold and confinement in a molybdenum wall with different magnetic configurations on the EAST tokamak

A series of ELMy H-mode discharges were achieved on Experimental Advanced Superconducting Tokamak (EAST) with low hybrid wave (P_LHW = 0.5-1.7 MW at 2.45 GHz) and ion cyclotron resonance frequencies (P_ICRF = 0.5-2 MW) as the auxiliary heating power in 2012. In double-null (DN) configurations, the experimental power threshold with a molybdenum wall (2012) appears to be lower than that with a graphite wall (2010). For lower single null (LSN) plasmas, the lower X-point configuration has a lower power threshold, and a significant reduction (∼25%) in the H-mode power threshold with 3.4 cm X-point movement is achieved. The lower X-point configuration on EAST has higher dR_sep below zero (closer to the DN configuration). Better energy confinement is observed in DN compared with single null (SN) at the same power loss. For reasons not understood, when the ion grad-B drift is in a favourable direction for H-mode access (towards the X-point) for EAST's LSN configuration, H-mode is achieved in upper single null (USN) configurations, but not in LSN.