ELM Control at the L-H Transition Achieved by Pellet Pacing in the All-metal Wall Tokamaks ASDEX Upgrade and JET
Operating ITER in the reference inductive scenario at the design values of IP = 15MA and QDT = 10 needs to achieve good H-mode confinement relying on the presence of an edge transport barrier and the height of the plasma pedestal is a key to performance. Strong gradients evolving at the edge can drive MHD instabilities resulting in an Edge Localized Mode (ELM) producing rapid energy burst from the pedestal region. Without dedicated control ELM resulting impulsive heat loads on plasma facing materials in ITER becomes critical for operation at IP 9.5MA, progressing beyond would result in an intolerable short life time of the divertor plates. Currently, there are several options considered for this inevitable ELM actuation, but all of them need further validation for the ITER tasks. Evidently, the main task in this context is to achieve sufficient mitigation of the peak power flux to divertor in according scenarios, either by suppression or mitigation of ELMs. ELM control requirements in ITER have recently received focussed attention in relation with the proposal to start ITER operation with a Tungsten (W) divertor, which was originally foreseen for the beginning of nuclear operations (DD and DT plasmas) and is now being considered also for the start of ITER operation in the non-nuclear phase (H and He plasmas).