Characteristics of edge-localized modes in the experimental advanced superconducting tokamak (EAST)

Abstract

Edge-localized modes (ELMs) are the focus of tokamak edge physics studies because the large heat loads associated with ELMs have great impact on the divertor design of future reactor-grade tokamaks such as ITER. In the experimental advanced superconducting tokamak (EAST), the first ELMy high confinement modes (H-modes) were obtained with 1 MW lower hybrid wave power in conjunction with wall conditioning by lithium (Li) evaporation and real-time Li powder injection. The ELMs in EAST at this heating power are mostly type-III ELMs. They were observed close to the H-mode threshold power and produced small energy dumps (1–2% of the stored energy). Type-III ELMs produced a time-averaged peak heat flux of about 2 MW m−2 on the target plate, a value which is ∼10 times larger than that of ELM-free phases. A few isolated and large type-I-like ELM events were also observed in EAST with an energy loss of up to 5% of the stored energy. Statistically, the ELM frequencies are several hundred hertz and the frequency appears to decrease with q95, the safety factor at 95% of the flux surface. When an ion cyclotron resonance frequency wave was injected during the H-mode phases, the ELM repetition frequency increased immediately. The frequency and amplitude of type-III ELMs can be effectively influenced by puffing impurity argon gas.