Description
For the first time, identity and similarity experiments between DIII-D and WEST were performed in the ITER "hybrid-like" regime during dedicated campaigns on the two facilities in 2025. These experiments exploit the complementary capabilities of the two facilities and aim to illuminate the path toward combined high fusion performance with high-normalised pressure N (DIII-D) and long-pulse scenarios (WEST) in a tungsten environment.
The matched parameters include elongation, positive triangularity, ion ∇B drift direction toward X-point, safety factor profile, and core dimensionless physics quantities such as normalized pressure, normalized gyroradius, electron collisionality, and the ion to electron temperature ratio, Ti/Te. Core transport physics is explored across different aspect ratios (R/a) (3 at DIII-D and 5 on WEST). DIII-D accessed high- regimes (strong electromagnetic effects) under low injected torque (~0 ± 0.5 N·m) using high heating power, while scanning heating mix (ion vs electron), , Ti/Te, core radiation via controlled tungsten injection using the Laser Blow-Off system. WEST extended operation toward long duration pulses using its actively cooled tungsten divertor. Boron impurity injection was scanned on WEST to control edge conditions and core performance.
It is found that core confinement improves—manifested in higher electron temperature, total energy content, neutron rate, and ion temperature — under conditions of low separatrix density, consistent with previous observations. The ratio of the thermal energy confinement time (τE) to the volume-averaged electron–ion collisional heat exchange time (τe-i) emerges as a key parameter for enhancing ion heating and potentially facilitating H-mode access in electron-heated regimes. Conditions for both H-mode access and ion heating in electron-dominated regimes on WEST and DIII-D are compared (role of aspect ratio, ion heating versus electron heating). An outlook is also provided on extending the campaign by matching aspect ratio, increasing the ECRH power level, or replicating the dimensionless studies in negative-triangularity configurations with similar L-mode edges.
The first-of-a-kind coordinated DIII-D and WEST experiments provide a unique multi-machine dataset to validate predictive models and support extrapolation toward ITER and future fusion power plants, leveraging the complementary strengths of the two facilities.