Speaker
Description
Consistent with the cost and complexity of the ITER full tungsten (W) actively cooled divertor, a comprehensive physics basis has been established over more than two decades (see [1] and references therein). This first-of-a-kind component, of unprecedented size and lifetime requirement, has now moved into the series production phase [2]. This does not mean, however, that physics studies in support of the ITER divertor and its operation no longer take place. Rather, exploration has continued, from the point of view of both stationary and transient operation. It must also now focus on aspects related to the new ITER Research Plan (IRP) which accompanies the 2024 re-baselining activity [3,4]. The purpose of the present submission is to summarise some of the key new analyses undertaken since the physics basis was last summarised in the 3rd meeting of this IAEA TM Divertor Concepts series held in 2019.
As the component which intercepts >90% of the thermal plasma power exhausted into the scrape-off layer (SOL), the principal design driver for the ITER divertor has always been stationary power loading. Evidently, burning plasmas (PSOL ≥ 100 MW) represent the most severe test, both in terms of power density and fluence, but it is also important to assess the loading to be expected in the earlier, lower power phases of ITER operation, specifically the Start of Research Operations (SRO) campaign in the new baseline.
This SRO phase contains a short deuterium (DD) H-mode campaign, a primary objective of which is to test edge localized mode (ELM) control schemes in advance of the DT phase. This has motivated a detailed EMC3-Eirene study of divertor conditions and detachment access in the presence of resonant magnetic perturbations (RMP), using MARS-F plasma response modeling to provide realistic magnetic field geometries resulting from RMP coil phasings which maximise the X-point displacement figure of merit known to be correlated with ELM suppression in current devices [5]. Scenarios at n = 4 are found to be preferred over n = 3 or hybrid n = 3,4 perturbations, yielding smaller magnetic footprint width on the target and with the helical lobe structures situated closer to the original, unperturbed strike point, facilitating momentum and radiative losses (i.e. detachment).
For non-perturbed configurations, new, drift activated SOLPS-ITER studies have been dedicated to the assessment of performance during the DD H-mode phase, demonstrating that at the maximum expected PSOL ~ 40 MW, impurity seeding is likely to be required for both power load and upstream separatrix density control [6]. Efforts have also been directed towards new burning plasma simulations deploying a higher fidelity model of the divertor structure, permitting a more realistic accounting of neutral bypass conductances [7]. This generates neutral recirculation patterns absent in the existing SOLPS database, reducing far SOL target plasma temperatures and neutral pressures at the pumping duct, with implications for W target erosion, He exhaust and upstream He separatrix concentrations.
Regarding the key issue of transient loading, extensive simulations have been performed of a variety of situations in which ITER divertor W monoblock (MB) melting may occur under thermal plasma impact. This is encouraged by several years of favourable experiment-theory benchmarking in current tokamaks and has been made possible by the development of a new melt dynamics code, MEMENTO, retaining much of the physics model contained within the MEMOS-U code, previously used for ITER W melt estimates. Three issues specific to the divertor have been examined: the consequences of repetitive MB top surface melting driven by uncontrolled Type I ELMs [8], the threshold for ELM-driven toroidal gap edge melting and required ELM mitigation levels in the first SRO DD H-mode plasmas [9], and the melt damage to be expected on the upper outer divertor baffle region during unmitigated downward going disruption current quenches.
References
[1] R. A. Pitts et al., Nucl. Mater. Energy 20 (2019) 100696
[2] T. Hirai et al., “Manufacturing of the ITER tungsten divertor – prototyping/qualification and status of series production”, this conference
[3] A. Loarte et al., Plasma Phys. Control. Fusion 67 (2025) 065023
[4] R. A. Pitts et al., Nucl. Mater. Energy 42 (2025) 101854
[5] J. Van Blarcum et al., to be submitted to Nucl. Fusion
[6] A. Pshenov et al., accepted for PET 2025
[7] A. Pshenov et al., Nucl. Mater. Energy 42 (2025) 101851
[8] K. Paschalidis et al., Nucl. Fusion 64 (2024) 126022
[9] K. Paschalidis et al., Nucl. Mater. Energy 44 (2025) 101955
| Speaker's title | Mr |
|---|---|
| Speaker's Affiliation | ITER Organization |
| Member State or IGO | ITER Organization |
