Overview of the WEST contributions to the new ITER baseline and fusion power plants

Abstract In 2023–2025, WEST has developed robust long pulse discharges and reached duration exceeding 1000 s (record 1337 s), supported by a predict first approach. Reliable machine operation was key to achieving those performances. WEST is equipped with a fully actively cooled ITER grade divertor and has produced ITER relevant heat fluxes (up to 12 MW m −2 ) and particle fluence (over 10 27 D m −2 ). Cracks have been observed on the top surface of the mono-blocks, but do not hamper the divertor power exhaust capability so far. Significant erosion has been observed in the strike point area while thick deposited layers built up on the high field side of the divertor. Those deposited layers are prone to flaking, leading to impurity ingress into the plasma hampering plasma operation. A laser cleaning procedure has been developed to remove those deposited layers during shutdown. With the objective to mitigate tungsten erosion, a cold divertor X -point radiator (XPR) regime has been developed and controlled for more than 30 s. The transition into an XPR was modelled with the SOLEDGE code. WEST has also addressed urgent R&D issues in support of the tungsten first wall (FW) planned in the new ITER baseline, to inform the design of the ITER boronization system and characterize runaway impact. It was confirmed that glow discharge boronization (GDB) is required to ensure a robust plasma start-up. It was also shown that a non-uniform GDB is sufficiently efficient, and is less asymmetric than anticipated from modelling. WEST has produced dedicated run-away beam crash on the inboard limiter to validate the models of run-away damage in ITER. In the next two years, 3 MW of ECRH (electron cyclotron resonance heating) will be made available to extend the operational domain to H-mode and control tungsten transport. Beyond 2027, WEST plans to produce long pulses at higher power by upgrading its FW to improve power exhaust and operate with an optimized ITER like configuration.