Progress and issues in understanding the physics of ELM dynamics, ELM mitigation, and ELM control

Abstract

Recent experimental progress in understanding the dynamics of type I ELM, small/no ELM regimes to achieve ELM mitigation and active ELM controls is reviewed. As for the type I ELM dynamics, the smaller growth rate of the ELM precursor relative to the Alfvén frequency, the importance of ELM filaments to evaluate the ELM heat load, the evolution of pedestal pressure in the recovery phase, and the effects of edge toroidal rotation and toroidal field ripple on ELM energy loss have been observed in many devices. In low collisionality (ve*) small/no ELM regimes, the type V ELM has been obtained with one or two filaments in ve*<1 condition. Small normalized ELM energy loss less than 1% has been achieved in the grassy ELM regime in non-rotating plasmas. The highest pedestal pressure has been achieved with smaller edge toroidal rotation counter to the plasma current in the QH-mode. ELM control/suppression by pellet pacing and external magnetic field perturbation has been demonstrated, and so that a design activity of ELM control coils for ITER has started. Various effects of the edge toroidal rotation upon ELM characteristics have been found such as ELM energy loss (ELM frequency) in the type I ELM regime and the grassy ELM regime, changes in edge harmonic oscillation and achievable pedestal pressure in the QH-mode regime, and a screening effect in evaluation of island formation by ELM control coils.