Effect of B-field dependent particle drifts on ELM behavior in the DIII-D boundary plasma

Abstract

Edge localized mode (ELM) effects in the DIII-D pedestal and boundary plasmas were measured with multiple fast diagnostics in matched, lower single-null, ELMing H-mode discharges with the ion B · $B drift either toward or away from the divertor. Data show a strong dependence of the delay in inner vs. outer divertor ELM D a on drift direction, and a weaker drift dependence of the inner vs. outer delay of P rad , in addition to the strong density dependence seen in previous work. Time dependent boundary plasma modeling during an ELM was done with the UEDGE code including a six-species fluid carbon model and the effect of B-field induced particle drifts. The ELM was modeled as an instantaneous, outer midplane peaked, increase of diffusion coefficients from the top of the pedestal to the SOL. The simulations show delays in the inner vs. outer divertor ELM transients that are similar to the measured delays at moderate density.

Structure, stability and ELM dynamics of the H-mode pedestal in DIII-D

“…The radial velocity decreases with the radius in the SOL. Parallel velocity of the density perturbation, inferred from the relative timing of the D α pulses in the two divertors, approached the sound speed of ions at the pedestal temperature [67,68].…”