A Comparison of High Recycling H-mode Regimes on Alcator C-Mod and JET

Attempts were made to reproduce on JET the favorable EDA-regime found on Alcator C-Mod. This regime combines good energy confinement without large ELMs. The conditions in C-Mod for obtaining EDA H-mode include high triangularity (δ_u ~δ_l>0.4), relatively high edge safety factor (q_95>3.5), high target density (bar n_e>1 ×10^20m-3), good wall conditions loaded with deuterium, and sufficient input power to exceed well the H-mode threshold. To reproduce these conditions in JET, the divertor cryopump was switched off, a high triangularity equilibrium was produced (δ_u ~δ_l>0.4) with two plasma currents (Ip=1.7MA and 1.2MA) and fixed toroidal field (Bt=2.7T) to give q95=4.2 and 5.6. Up to 10.5 MW of ICRF power was injected, which exceeded the H-mode threshold of about 8 MW. H-mode densities up to bar n_e=5×10^19m^-3 were achieved, but only Type I ELMy H-mode plasmas were obtained on JET.