Role of Poloidal $\mathbf{E}\times\mathbf{B}$ Drift in Divertor Heat Transport in DIII-D

TL;DR

Simulations of DIII-D plasmas reveal that poloidal E×B drifts significantly influence divertor heat transport, often dominating over electron conduction, which challenges existing conduction-limited models and impacts impurity radiation estimates.

Contribution

This study demonstrates the critical role of poloidal E×B drifts in divertor heat transport, emphasizing the need for full 2D modeling including drifts for accurate predictions.

Findings

Poloidal E×B drifts can dominate heat transport in the divertor.

The Lengyel integral approach underestimates radiated power by a factor of 6.

Full 2D simulations including drifts are necessary for reliable power exhaust predictions.

Abstract

Simulations for DIII-D high confinement mode plasmas with the multifluid code UEDGE show a strong role of poloidal $\mathbf{E}\times\mathbf{B}$ drifts on divertor heat transport, challenging the paradigm of conduction limited scrape-off layer (SOL) transport. While simulations with reduced drift magnitude are well aligned with the assumption that electron heat conduction dominates the SOL heat transport, simulations with drifts predict that the poloidal convective $\mathbf{E}\times\mathbf{B}$ heat transport dominates over electron heat conduction in both attached and detached conditions. Since poloidal $\mathbf{E}\times\mathbf{B}$ flow propagates across magnetic field lines, poloidal transport with shallow magnetic pitch angles can reach values that are of the same order as would be provided by sonic flows parallel to the field lines. These flows can lead to strongly convection dominated divertor heat transport, increasing the poloidal volume of radiative power front, consistent with previous measurements at DIII-D. Due to these convective flows, the Lengyel integral approach, assuming zero convective fraction, is expected to provide a pessimistic estimate for radiative capability of impurities in the divertor. For the DIII-D simulations shown here, the Lengyel integral approach underestimates the radiated power by a factor of 6, indicating that for reliable DIII-D divertor power exhaust predictions, full 2D calculations, including drifts, would be necessary.