Speaker
Description
Magnetic-confinement fusion energy (MFE) devices, including Pilot Plants and DEMOs, need to breed tritium if the D-T fuel cycle is used. Breeding blankets pose a new challenge for main wall plasma-facing component (PFC) design not faced until now since they must have thin (~mm’s) armoring to achieve a Tritium Breeding Ratio (TBR) > 1 [1]. By contrast, the ITER first wall thickness is ~10 cm and can handle up to ~ 5 MW/m2 of deposited power flux density [2] – an order of magnitude higher than expected by a breeder blanket wall [3]. In this work, this challenge is addressed by separating the function of the wall into 3 distinct regions; 1) thin blanket-wall interface; 2) divertor target region; and 3) main wall, which could include the divertor entrance as well as protection limiters around the blanket-wall. Here, the focus is on tokamaks because the scrape-off layer (SOL) in this MFE system is the most understood. Nonetheless, it is foreseeable that a similar separation of function applies to any MFE reactor concept.
The main wall PFCs purpose is the removal of SOL plasma fluxes (heat and ions) not captured by divertor targets before striking the blanket-wall interface. Controlling SOL plasma contact with this interface requires a balance between plasma transport parallel and perpendicular to the magnetic field. This work uses a new code, DIV3D, for SOL power handling that simulates this parallel/perpendicular balance as well as allows for non-axisymmetric PFCs [4]. The code features strict global power conservation and estimates the cross-field plasma transport into magnetically-shadowed regions, which is significant when dealing with protection limiters that can produce large shadowed regions near the blanket-wall interface. This workflow can analyze limiter surfaces to protect against transient operation, e.g. off-normal events and the startup and ramp-down phases, as well as allows for a more compact vacuum volume by optimizing the wall to confined-plasma gap. This new tool and proposed PFC workflow is aiming for a more general and systematic description of plasma loading to MFE PFC surfaces.
Work supported in part by US DOE under DE-AC05-00OR22725 and DE-FC02-04ER54698.
[1] P.C. Stangeby, E.A. Unterberg et al., Plasma Phys. Control. Fusion 64 (2022) 055018.
[2] R. Mitteau et al., J. Nucl.Mater. 463(2015) 411.
[3] Y. Miyoshi et al., Fusion Eng. Des. 151(2020) 111394.
[4] J.H. Nichols et al., Fusion Eng. Des. 219 (2025) 115278.