Description
The new 2024 ITER baseline introduces a tungsten (W) first wall (FW), requiring renewed assessments of plasma-wall interactions and their impact on achieving the Q=10 performance target. This contribution provides a brief update of the status of ITER, and focusses on assessments of how the new wall material will impact key phases of ITER scenarios, from burn-through in limiter configuration, through diverted L-modes and finally, to the principal objective of burning plasma operation in H-mode. It details the implementation of risk mitigation measures, in particular the boronization system, which is critical for plasma start-up as demonstrated in dedicated experiments performed in WEST and ASDEX Upgrade. This overview also addresses the important issue of fuel retention and recovery strategies.
Throughout the limiter phase of ITER plasma scenarios, W erosion, core W contamination and edge power flow are coupled in an experimentally confirmed strongly self-regulated system, resulting in high core radiation and advantageously lowering power fluxes to the FW surface, but requiring central electron cyclotron heating (ECH) to prevent uncontrolled W accumulation. For L-mode diverted plasmas, central ECH also enables operation with moderate core radiated fractions from W wall sources, consistent with the range observed in current experiments with W plasma-facing components. For Q ≥ 10 H-mode scenarios, assumed to have no ELMs (either by active control or by access to naturally ELM-free plasmas compatible with Q ≥ 10), the full W pathway from source to core is quantified by combining new wide grid plasma boundary simulations, where wall and divertor loads are set within design specifications, with erosion source modelling to predict the W concentration at the separatrix, coupled to the core through state-of-the-art integrated modelling. This approach improves on the first studies performed for the re-baseline by maintaining consistent W transport assumptions across codes to provide a realistic assessment of the W source and transport. The analysis confirms, with greater confidence in the W source modelling, the key finding of the initial physics studies in support of the re-baseline, that the risk to the 500 MW fusion power target of switching to an all-W ITER is mitigated by the increased ECH power in the re-baseline, although with a reduction of Q for the highest W erosion sources for wall loads reaching their design limits.