First DIII-D–WEST Hybrid Scenario Similarity Experiments for ITER-Relevant Long-Pulse Operation

For the first time, similarity experiments between DIII-D and WEST have been performed in the ITER "hybrid-like" regime. Matched parameters include elongation, triangularity, ion ∇B drift toward the X-point, q-profile, and core normalized quantities (β_e, ρ_e*, ν_e*, T_i/T_e, Mach number). Physics of the core transport is explored with different aspect ratio (R/a) values (typically 3 at DIII-D and 5 on WEST). DIII-D explored high-beta conditions (electromagnetic effect) with low torque (~0 ± 0.5 N·m) via high heating power (up to 6 MW NBI and 2 MW ECRH powers), while scanning the heating mix (ion vs electron), beta, T_e/T_i, core radiation through controlled tungsten injection with the Laser Blow-Off system, and 3-D magnetic fields perturbation. WEST extended toward long-duration pulses using its actively cooled W-divertor, achieving hot-electron regimes with reduced tungsten levels. Boron and nitrogen seeding were scanned on WEST to reduce W influx and control edge conditions. It is found that core confinement is improved (higher electron temperature, total energy content, neutron rate and ion temperature) in conditions of low separatrix density [Bourdelle 2023 et al Nucl. Fusion 63 (2023) 056021]. These first-of-a-kind coordinated experiments provide a unique multi-machine dataset to validate predictive models for ITER hybrid scenario optimization under diverse core and edge conditions.