Integrated simulation of ELM energy loss and cycle in improved H-mode plasmas

Abstract

The energy loss due to an edge localized mode (ELM) crash and its cycle have been studied by using an integrated core 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 collisionality and the ELM frequency increases linearly with the input power, as seen in experiments of type-I ELMs. A transport model with the neoclassical transport in the pedestal connected to the SOL parallel transport reproduces a lowered inter-ELM transport in the case of low collisionality so that the ELM loss power is enhanced as observed in experiments. The inter-ELM energy confinement time evaluated from simulation results agrees with the scaling based on the JT-60U data. The steep pressure gradient in the core just beyond the pedestal top, desirable for improved H-mode plasmas with the H H98y2 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 in the core beyond the pedestal top broadens eigenfunction profiles of unstable modes and possibly induces subsequent instabilities. In the subsequent instabilities, when a large energy is transported to the vicinity of the separatrix by the instabilities, a subsequent instability arises near the separatrix and makes an additional loss.

Integrated Modeling of Whole Tokamak Plasma

“…This integrated code reproduced the experimentally observed collisionality dependence of ELM energy loss and showed that the collisionality dependence is caused by the bootstrap current, the SOL parallel conductive transport and the equipartition effect [28]. The integrtated code also clarified that the steep pressure gradient inside the top of pedestal enhances the ELM energy loss [31], which is validated by the experimental data in JT-60U [32].…”

Negative Triangularity Tokamak as Fusion Energy System

“…The increase of the surface current (i.e. edge bootstrap current) destabilize lower n (toroidal mode number) peeling eigenmode, which has larger radial extent [22]. Mitigation of ELM strength becomes essential for ITER and especially for future DEMO reactor, which necessarily operates high duty factor to effectively breed tritium.…”

Divertor Study on DEMO Reactor

“…Independence of each module is almost kept and therefore model improvement or implementation of new model become possible with small effort. The MPMD system has been already introduced to the integration of the SONIC suite and the 1.5 D core transport code TOPICS [18][19][20] and the time evolution of the L-H transition has been successfully simulated selfconsistently [21,22]. Recently, the MPMD system has been improved mainly in the viewpoint of the data exchange method and restructuring of the SONIC suite, i.e., SOL-DOR/NEUT2D/IMPMC, on the new MPMD system is ongoing.…”