Test of the Eich model for ELM energy densities in DIII-D

摘要

Introduction The standard H-mode is subject to edge-localized-modes (ELMs) leading to the collapse of the edge pressure gradient and bootstrap current in a repetitive cycle. The ELMs provide impurity transport out of the plasma, but also produce pulsed heat loads on plasma facing components. While the loads are benign on present day devices, they will likely cause erosion, melting and recrystallization in the divertor of ITER and future power plants~(1,2). Recent tungsten tests simulating pulsed loads revealed material tolerance limits below expected ITER loads, making uncontrolled ELMs a major operational constraint. To define mitigation requirements, it is necessary to understand the scaling of ELM heat loads and their dependence on plasma parameters. Based on experimental findings on ASDEX Upgrade (AUG) and JET a model was put forward proposing that parallel ELM energy densities ε_(||) scale with pedestal electron pressure p_(e,ped) as {formula} from here on referred to as the Eich model~3. ε_(||) is the maximum of the time-integrated heat flux during ELMs mapped onto the divertor, a_(pol) the minor radius weighted by the elongation and {formula} the ratio of the magnetic fields at the outer midplane. As the model scales Bp favourably towards ITER's active phase compared to previous considerations ~2, the work presented here is dedicated to testing the Eich model on DIII-D. Additionally, the origin of the large lx-3x scatter typically observed about the scaling, and the role of plasma parameters (in particular pedestal pressure and collisionality) on ELM energy densities are investigated.