Detachment scalings derived from 1D scrape-off-layer simulations

TL;DR

This paper uses 1D scrape-off-layer simulations to explore detachment physics in fusion devices, aiming to inform real-time control strategies and compare with existing models and simulations.

Contribution

It demonstrates the capability of Hermes-3 simulations to reproduce detachment behavior and compares their scalings with established models and SOLPS results, highlighting areas for improvement.

Findings

Simulations reproduce target ion flux rollover during detachment onset.

Steady-state results match predictions from the Lengyel-Goedheer model.

Time-dependent effects significantly impact detachment dynamics.

Abstract

Fusion power plants will require detachment to mitigate sputtering and keep divertor heat fluxes at tolerable levels. Controlling detachment on these devices may require the use of real-time scrape-off-layer modeling to complement the limited set of available diagnostics. In this work, we use the configurable Hermes-3 edge modeling framework to perform time-dependent, fixed-fraction-impurity 1D detachment simulations. Although currently far from real-time, these simulations are used to investigate time-dependent effects and the minimum physics set required for control-relevant modeling. We show that these simulations reproduce the expected rollover of the target ion flux - a typical characteristic of detachment onset. We also perform scans of the input heat flux and impurity concentration and show that the steady-state results closely match the scalings predicted by the 0D time-independent Lengyel-Goedheer model. This allows us to indirectly compare to SOLPS simulations, which find a similar scaling but a lower value for the impurity concentration required for detachment for given upstream conditions. We use this result to suggest a series of improvements for the Hermes simulations, and finally show simulations demonstrating the impact of time-dependence.