Toroidal Rotation: A Game-Changer for Tokamak Divertor Design

Scientists have observed an uneven distribution of plasma particles striking the inner divertor target more than the outer one in tokamaks. Understanding this pattern is crucial for designing future fusion systems, as engineers need to predict exhaust particle landing locations to build effective divertors.

Previous explanations primarily focused on cross-field drifts, the sideways movement of particles across magnetic field lines within the divertor. However, simulations incorporating only cross-field drifts did not accurately reproduce the observed uneven particle striking pattern from experiments.

Unlocking the Plasma Distribution Mystery

New simulations indicate that toroidal rotation, the motion of particles around the tokamak, is a key factor in plasma particle distribution within the exhaust system. Researchers utilized the SOLPS-ITER modeling code to simulate particle paths.

The study, published in Physical Review Letters, demonstrates that combining plasma core rotation with cross-field drifts enables simulations to match experimental measurements. This alignment is considered critical for designing future fusion power plants.

According to Eric Emdee, lead author and associate research physicist at Princeton Plasma Physics Laboratory (PPPL), plasma flow involves both cross-field flow (sideways drift) and parallel flow (travel along magnetic field lines).

"The study indicates that parallel flow, driven by the rotating core, is as significant as cross-field flow in creating the observed asymmetry."

Simulations Align with Reality

Simulations performed using the DIII-D tokamak in California achieved experimental matching only when the measured core rotation of 88.4 kilometers per second was included. The combined impact of rotation and cross-field drifts exceeded the effect of either component individually.

This suggests that accurate prediction of exhaust behavior in future fusion systems necessitates considering the influence of the rotating plasma core on edge flows for improved divertor design.

The research team included Eric Emdee, Laszlo Horvath, Alessandro Bortolon, George Wilkie, Shaun Haskey (all from PPPL), Raúl Gerrú Migueláñez (MIT), and Florian Laggner (North Carolina State University).

Funding for this work was provided by the DOE's Office of Fusion Energy Sciences, utilizing the DIII-D National Fusion Facility.