Speaker
Description
The DIII-D National Fusion Facility is preparing for a transition from graphite to tungsten (W) plasma-facing components to enable reactor-relevant studies of plasma scenarios, core-edge integration, and plasma–material interaction for next-step fusion devices.
Leveraging DIII-D’s unique capability for short-pulse, high-performance operation with flexible shaping, advanced actuator control, and comprehensive diagnostics, the new metal-wall environment would also accommodate innovative divertor concepts and iterative design optimization. This upgrade would directly support the mission of future fusion pilot plants (FPPs) by enabling validation of plasma boundary physics, impurity transport, and material performance in high-Z conditions. The Full Wall Change-Out, targeted for 2029, would proceed in stages, prioritizing W installation in the highest heat and particle flux regions while preserving flexibility for future expansion.
A structured Physics Validation Review (PVR) is underway to ensure compatibility of the full-metal configuration with DIII-D’s present scenario portfolio. Preliminary PVR results suggest that key advanced scenarios, including Advanced Tokamak, Negative Triangularity, and Quiescent H-mode, remain viable in high-Z environments, provided core W accumulation is effectively managed. Active mitigation tools under evaluation include strike-point sweeping, ECH impurity flush-out, seeding of radiative impurities, and optimized plasma shaping.
Updated analysis of heat fluxes and fast ion losses identifies the main strike-point regions, upper inner wall, and upper baffle as critical areas requiring either bulk W or tungsten coatings. The remaining wall can be made out of stainless steel or molybdenum without significantly increasing high-Z impurity levels. Erosion estimates confirm that W-based alloys self-stabilize to W-like surfaces within hours of operation. Runaway-electron calculations show that beam currents up to 500–900 kA remain benign for W, assuming melting limits of 3–5 MJ m⁻² and deposition areas of 0.1–0.5 m². Maintaining tile alignment within ≤ 0.5 mm ensures that even leading edges stay within safe thermal limits.
Additional infrared and visible cameras, thermocouples, and interlocks for surface monitoring would be required to enable safe metal-wall operation. The PVR incorporates lessons from JET and ASDEX-Upgrade showing that robust startup, ELM, and impurity control are achievable in full-metal environments with active plasma–surface monitoring. The tungsten wall at DIII-D will provide a versatile platform to advance and validate the physics basis and control strategies for ITER; long-pulse tungsten devices such as EAST, WEST, and KSTAR; and future FPPs.
This work was supported by the US DOE under DE-AC02-09CH11466, DE-FC02-04ER54698, DE-NA0003525, DE-SC0014264, DE-AC05-00OR22725, DE-SC0023378, DE-AC52-07NA27344, and DE-SC0022270.