Description
Oak Ridge National Laboratory is participating in MAST-U research with a focus on boundary plasma diagnosis and modeling related to power exhaust. Demonstrating control of reactor-scale heat fluxes with effective core-edge integration is a major part of the MAST-U mission, leveraging its unique capabilities such as the Super-X divertor. The ORNL activities are primarily in three categories: 1) advanced plasma measurement and synthetic diagnostics, 2) demonstrating exhaust control strategies with validated modeling, and 3) core-edge integration.
ORNL operates and supports key bolometric and spectroscopic diagnostics that are leveraged for boundary plasma studies. Resistive [1] and infrared video bolometers [2] (with an upper IRVB system in development) are used for power balance [3] and radiation pattern measurements [4]. A spectrometer and CCD camera originally on JET have been installed on MAST-U with corresponding synthetic diagnostic twins implemented in Cherab. These measurements enable inference of the divertor electron temperature and evaluation of detachment dynamics, critical quantities for assessing core-edge integration. ORNL also supports analysis of high spatial resolution edge spectrometers, used to measure the neutral density and evaluate recycling and neutral leakage.
Plasma boundary modeling is performed using the SOLPS-ITER code. Recent results show that cross-field drifts may explain a measured asymmetry between the upper and lower divertor conditions [5], although future experiments have been proposed to untangle the relative effects of the upper/lower magnetic bias and the scaling with divertor temperature. For self-consistent boundary modeling, the SOLPS results are coupled with core and pedestal modeling and measurements. Experiments scheduled for the MU05 campaign will validate a flux-based model for pedestal density predictions that can be used to constrain EPED and improve the core-edge coupling.
ORNL is also involved in developing scenarios for advanced divertor configurations, including X divertor, snowflake and dynamic double null operation. These will be supported by modeling of the far-SOL plasma using the wide grid version of SOLPS, and simulation of the effect of plasma and magnetic transients on the divertor conditions.
This work has been funded in part by the EPSRC Fusion Grant 2022/27 [grant number EP/W006839/1] and the US DOE under contract DE-AC05-00OR22725.
[1] Lovell, J, et al, RSI 94 (2023) 023509
[2] Federici, F, et al, RSI 95 (2024) 103525
[3] Lovell, J, et al, NME 41 (2024) 101779
[4] Federici, F, et al, NME 41 (2024) 101758
[5] Paradela Perez, I, Nuclear Fusion 65 (2025) 66026