Speaker
Description
Fusion energy is accelerating through conventional (DEMO) and alternative compact reactor designs, that are potentially faster and cheaper to build (e.g., ARC, STEP). Power exhaust is a key challenge and a potential show-stopper for all these designs. Recent experiment show the key benefits of strongly shaped Alternative Divertor Configurations (ADCs) [1-5], demonstrating their potential as a power exhaust solution. However, integration of ADCs in a reactor is complex: a compromise between power exhaust benefits and engineering feasibility is required [5].
Initial MAST-U results show a continuum of ADC optimisation through total flux expansion exists: modest, yet strategic, divertor shaping greatly enhanced power exhaust performance [3] and control [4]. To study this continuum, geometries with intermediate strike point position in between the MAST-U Super-X and Conventional geometrieswere compared. These intermediate geometries have less than half the total flux expansion increase of MAST-U’s Super-X divertor: lower than that of STEP [7] and comparable to that of SPARC [8], ARC [9] and the DEMO Super-X Divertor [6].
Crucially, the key benefits of the MAST-U Super-X Divertor over the Conventional Divertor are largely maintained for these geometries.
1. Target heat loads are reduced beyond geometric spreading expectations.
2. The sensitivity of detachment is drastically reduced, improving real-time power exhaust control [4].
3. Reducing the detachment onset without any adverse core impact increases the operational window of the detached regime. This improved core-edge compatibility can enable reactor operation at lower core power losses [6] and/or lower upstream densities/fuelling (relevant for ELM-free scenarios and fuel cycle limitations [7]) and/or lower impurity concentrations.
Studying the physics driving these benefits shows synergies between neutral baffling, poloidal leg length and total flux expansion. This shows power exhaust benefits can be obtained from strategic divertor shaping; consistent with reduced and full models, enabling improving power exhaust with relatively modest additional engineering complexity. This provides lessons on both divertor design – relevant for reactors - and exhaust physics/simulations and control [4] – relevant for ITER.
[1] C. Theiler, et al. This conference. [2] K. Lee. PRL. 2025. [3] D. Moulton. NF, 2024. [4] K. Verhaegh. Comm. Phys. 2025. [5] B. Kool. Nat. Energy, 2025. [6] R. Kembleton. FED 2022. [7] Xiang. 2021, NF; [8] Henderson. NF 2025; [9] Kuang, et al. JPP 2020; [10] Wigram, NF, 2019.