Predict-first integrated modeling of WEST long pulse operation with combined ECRH/ECCD and LHCD

Abstract The WEST tokamak operates long pulses up to 1337 s in a full-tungsten (W) environment, anticipating challenges of next-generation fusion devices. Recent predict-first long pulse experiments, conducted based on High-Fidelity Plasma Simulator (HFPS) simulations, culminated in a new record pulse and validated the modeling framework. In an electron-heated, via the Lower-Hybrid Current-Drive (LHCD), fully non-inductive regime with W impurities, overall performance in terms of triple product remains limited, and off-axis current drive can trigger core q -profile reversal, degrading MHD stability. The new 3 MW/1000 s Electron Cyclotron Resonance Heating and Current-drive (ECRH/ECCD) system under integration offers localized heating and current drive to mitigate these limits. In the present paper, building on the validation of the HFPS, a predict-first exercise is performed to prepare WEST long pulse operation with additional ECRH/ECCD. Simulations indicate that applying on-axis ECCD to an LHCD-heated plasma enhances the stored energy content by 10%, improves the plasma core stability, and provides similar levels of non-inductive current than LHCD alone. Moreover, ECCD modifies the LHCD deposition location, offering significant q -profile tailoring capabilities. Off-axis ECCD operation provides access to advanced scenarios: raising the central q above 2 or suppressing turbulence sufficiently to trigger internal transport barriers when combined with strong core heating, yet with increased risk to core tearing instability. These results outline strategies for combined LHCD/ECRH/ECCD operation in WEST and stress the importance of the ECCD launching angle optimization for performance and stability.