Suppression of large edge localized modes in high confinement DIII-D plasmas with a stochastic magnetic boundary

Abstract

Large 70Hz Type-I edge localized modes (ELMs) are converted into small 130Hz oscillations using edge resonant magnetic perturbations (RMPs) from a coil with currents ⩽0.4% Ip in double null DIII-D plasmas. When the RMP is properly phased with respect to the background field errors, all but a few isolated ELM-like events are suppressed. The impulsive pedestal energy loss ΔEELM/Δt1/2 to the scrape-of layer is reduced a factor of ⩾20 relative to the Type-I ELMs and the core confinement is unaffected by the perturbation field. Significant changes in the properties of the ELMs are also observed when edge RMPs are applied to lower single null plasmas but the nature of these changes are much more complex. Both lower single null and double null plasmas are being studied to determine how ELM control techniques based on the application of edge RMPs can be expected to scale to future devices such as ITER.