Type-I ELM mitigation in high triangularity and steady state regimes using low n external magnetic perturbation fields on JET

JET results show that low n perturbation fields generated by an external coil system can be used to control frequency and energy loss of type-I ELMs. ELM mitigation using the EFCCs has been investigated in standard ELMy H-modes at low and ITER-like triangularity and in a high beta steady-state scenario. With n = 1 fields the ELM frequency could be increased by a factor of 4 and the ELM energy loss became less than 2%, compatible with the upper limit of acceptable ELM losses for ITER. The application of n = 2 fields shows similar features, although the maximum perturbation field strength was limited. An operational window for ELM mitigation was always found below the threshold for locked modes excited by the n = 1 perturbation field. The small n = 1 component of the n = 2 field make it even more unlikely to seed a locked mode in the plasma and offers an additional advantage for low plasma rotation as anticipated in ITER. This offers an attractive solution for ITER where type-I ELM energy losses are predicted to be too large and control or mitigation of ELMs will be required.