Application of edge codes to the new high-field tokamaks*

A new generation of high-field tokamaks are being designed for the near future. Such devices present potential benefits but also challenges - narrow heat flux widths associated with high poloidal fields make the divertor heat flux problem particularly difficult. The Divertor Tokamak Test (DTT) facility – a high-field device compared to current tokamaks, reaching 6T on-axis – will be an important step towards finding a solution. Simulation codes provide useful tools to design and assess divertor scenarios, but will encounter their own challenges in high-field devices, with narrow particle and energy channels and steep gradients. In this work, to improve the DTT divertor modelling capability, a comparison study is performed between three edge-plasma codes: SOLPS-ITER, UEDGE and SOLEDGE2D, to assess and understand the differences in code predictions, including a model validation study for a high-field, narrow SOL width discharge in Alcator C-Mod. Modelling will then move on to examine advanced long-leg configurations. Results find limitations in fluid neutral models opposed to kinetic solvers, the importance of charge-exchange models for molecular hydrogen, as well as mesh extension effects – all showing notable impact on predictions in the high-field, high fusion power context.