Speaker
Description
The ITER 2024 re-baseline defines a revised approach to reach the main burning plasma objective. A key component of this strategy is the switch from Be to W main wall armour, making ITER a full-W device from the beginning of operations. In fact, the new wall becomes two walls, with a Temporary First Wall (TFW) in place for the “Start of Research Operations” campaign (SRO) in the revised ITER Research Plan, followed by the final, actively cooled FW in place for DT operations. Both are being designed in parallel, but the lengthy DT wall procurement means that the second cannot benefit from experience gained with the first. Both must interface with the same set of Blanket shield blocks, but the TFW is an inertially cooled component with a mandate to permit achievement of the principal SRO objectives of 15 MA / 5.3 T hydrogen L-modes, 7.5 MA / 2.65 T deuterium H-modes. These two factors are driving TFW design choices, e.g.: thermal envelope defined by an entire pulse rather than a single (burning plasma) operating heat flux for the DT wall; standardizing FW panel tiles, simplified shaping, deployment of armour variants in different locations (e.g. bulk W, W heavy alloy).
The new walls benefit from improvements in physics understanding of both stationary and transient heat loads over the past decade since the final design review of the original Be variant. Disruption transients constitute the main rationale for the TFW, which will allow mitigation and avoidance techniques to be developed during SRO without fear of water leaks. In turn, this relaxes the need for the DT wall design to account for the worst-case disruption current quenches since it is assumed that the SRO Research Plan will guide improved operation. Nevertheless, the spectre of runaway electrons (RE) can never be completely alleviated by experience gained in SRO; Compton and tritium decay beta seed electrons will appear for the first time in the DT phase. Much improved understanding of RE impact, from incoming energy distribution to deposition in the material and subsequent thermal transfer, have driven an increase in design armour thickness in areas of the DT wall expected to be critical for RE interactions.
The paper presents the physics basis for the loads which are determining the design of the new ITER W walls. It will also provide an update on the wall designs at the time of the conference.