@article{9233,
  author = {B. Kool and M. Lennholm and A. Parrot and P. A. Figueiredo and G. L. Derks and O. Bardsley and T.A. Wijkamp and S. P. Kobussen and L. Ceelen and M. van Berkel and M. Lord and A. Cureton and S. Henderson and N. J. Conway and J. Lovell and N. Lonigro and K. Verhaegh and STEP Team and MAST-U Team and EUROfusion Tokamak Exploitation Team},
  title = {From MAST-U to STEP: Power exhaust control challenges and opportunities},
  abstract = {This work explores the challenges and opportunities for power exhaust control in STEP, informed by dedicated MAST-U experiments. The STEP system primarily relies on hydrogenic and argon gas injection into the divertors, compensating for transients originating in the plasma core. Fast transients (>10 Hz) that evolve too quickly for actuators to compensate must be absorbed passively; the enhanced transient buffering of the foreseen long-legged divertor provides a clear advantage over conventional geometries, as demonstrated in the MAST-U Super-X divertor. Experiments further indicate that STEP’s tight divertor baffling enables near-independent control of the upper and lower divertors. The most challenging transients are expected from power-sharing fluctuations, as MAST-U experiments observed extremely fast dynamics. Fluctuations from core pellet fuelling remain relatively benign due to the small pellet size according to simulations. Exhaust control in a reactor like STEP requires an integrated approach befitting its machine-critical nature. A predictive control element, integrated with core plasma control, allows pre-emptive preparation of the divertor for incoming transients. An observer-based diagnostic approach is foreseen to monitor the divertor in the challenging reactor environment, supported by an extended diagnostic set in the non-nuclear phase to validate the required dynamic models.},
  year = {2026},
  journal = {Fusion Engineering and Design},
  volume = {224},
  pages = {115602},
  doi = {10.1016/j.fusengdes.2025.115602},
  language = {eng},
}