H modes with good confinement and small ELMswith the characteristics of type II or grassy ELMs have been observed on ASDEX Upgrade.Such an ELM behaviour is essential to minimize erosion of the divertor tilesin any next step device. For the first time, operation with this favourableELM type could be demonstrated close to the Greenwald density.Even for such high densities, energy confinement times were close to recent H mode scalings. Highdensity even seems to be favourable, since steady state puretype II ELMy H mode phases on ASDEX Upgrade are obtained only above e/GW ⩾ 0.85. Additional requirements are q95 ⩾ 4.2 and an equilibrium close to a double null configurationwith an average triangularity δ = 0.40. For these small ELMs magnetic precursors are observed with a frequency of ≈ 30 kHz and dominantmode numbers of toroidally 3 and 4 and poloidally ⩾ 14.
Predictive transport modelling and MHD stability analysis of mixed type I-II ELMy H-mode JET plasmas