Double-null power-sharing dynamics in MAST-U
Maintaining an effective double-null configuration is expected to be challenging in reactor-scale tokamak devices. As divertor power-sharing is closely
linked to the magnetic topology, even small variations can lead to fast power sharing fluctuations which exacerbate the already daunting exhaust challenge. While the static aspects of double-null power-sharing have been extensively studied across various devices, this paper presents the first detailed investigation of its dynamic behaviour. We employ dedicated experiments in MAST-U, featuring perturbation frequencies up to 200 Hz. Our results clearly show no significant dynamic power-sharing damping in the considered frequency range: the divertor responds equally to both fast and slow perturbations. The response also aligns with quasi-static results from slow ramps, implying that static power-sharing models remain valid even for fast fluctuations. Consequently, we conclude that heat load mitigation schemes which rely on exploiting dynamical plasma power-sharing effects are unlikely to be effective. Some deviations from the otherwise linear behaviour are observed, alongside notable scatter and occasional
asymmetries between upwards and downwards trajectories. These variations may be linked to changes in core conditions, but the underlying mechanisms remain unclear and require further study.