Integrated Simulation of ELM Energy Loss and Cycle in Improved H-mode Plasmas

The energy loss due to an edge localized mode (ELM) crash and its cycle have been studied by using an integrated transport code with a stability code for peeling-ballooning modes and a transport model of scrape-off-layer (SOL) and divertor plasmas. The integrated code reproduces a series of ELMs with the following characteristics. The ELM energy loss increases with decreasing the collisionality and the ELM frequency increases linearly with the input power, as the same as experiments of type-I ELMs. A transport model with the pedestal neoclassical transport connected to the SOL parallel transport reproduces the inter-ELM transport, which decreases in the low collisionality so that the ELM loss power is enhanced as observed in experiments. The inter-ELM energy confinement time agrees with the scaling based on the JT-60U data. The steep pressure gradient inside the pedestal top, required for improved H-mode plasmas with the HH98y2 factor above unity, is found to enhance the ELM energy loss and reduce the ELM frequency so that the ELM loss power remains constant. The steep pressure gradient inside the pedestal top broadens the region of the ELM enhanced transport and induces subsequent instabilities. When the large energy is transported near to the separatrix by the instabilities, a subsequent instability arises near the separatrix and makes an additional loss.