Reassessing energy deposition for the ITER 5 MA vertical displacement event with an improved DINA model

Highlights: • Transient heat loads on ITER first wall from a 5MA VDE current quench are simulated. • Updated DINA disruption modeling code used to provide VDE scenarios. • Power loads and surface temperatures estimated with SMITER and MEMOS-U codes. • A new method for comparing halo current widths across fusion devices is proposed. • Beryllium first wall panels remain below melt threshold for all 5MA VDE variations. The beryllium (Be) main chamber wall interaction during a 5 MA/1.8 T upward, unmitigated VDE scenario, first analysed in [J. Coburn et al., Phys. Scr. T171 (2020) 014076] for ITER, has been re-evaluated using the latest energy deposition analysis software. Updates to the DINA disruption model are summarized, including an improved numerical convergence for the 0D power balance, limitations on the safety factor within the plasma core, and the choice to maintain a constant plasma + halo poloidal cross-section. Such updates result in a broad halo region and higher radiated power fractions compared to previous models. The new scenario lasts for ~75 ms and deposits ~29 MJ of energy, with the radial distribution of parallel heat flux $q_{\Vert }\left(r\right)$ resembling an exponential falloff with an effective ${\lambda }_q=75-198$ mm. A maximum halo width $w_h$ of 0.52 m at the outboard midplane is observed. SMITER field line tracing and energy deposition simulations calculate a $q_{\perp ,max}$ of ~83 MW/m² on the upper first wall panels (FWP). Heat transfer calculations with the MEMOS-U code show that the FWP surface temperature reaches ~1000 K, well below the Be melt threshold. Variations of this 5 MA scenario with Be impurity densities from 0 to 3∙10¹⁹ m⁻³ also remain below the melt threshold despite differences in energy deposition and duration. These results are in contrast to the early study which predicted melt damage to the first wall [J. Coburn et al., Phys. Scr. T171 (2020) 014076], and emphasize the importance of accurate models for the halo width $w_h$ and the heat flux distribution $q_{\Vert }\left(r\right)$ within that halo width. The 2020 halo model in DINA has been compared with halo current experiments on COMPASS, JET, and Alcator C-Mod, and the preliminary results build confidence in the broad halo width predictions. Results for the 5 MA VDE are compared with those for a 15 MA equivalent, generated using the new DINA model. At the higher current, significant melting of the upper FWP is to be expected.