Modelling the X-Point Target divertor and detachment stability in ARC V2A SOLEDGE2D simulations

The SOLEDGE2D code is employed to perform the first ARC full-domain simulations of the double-null X-Point Target (XPT) divertor, in the ARC V2A context. FPPs will require divertor plasma temperatures/fluxes to be reduced to levels that are compatible with divertor cooling technology and project to realistic lifetime erosion rates. Double-nulls, long-legs and secondary divertor X-points have been studied as potential solutions, with significant benefits observed in previous modelling/experiments [1,2]. The ARC design provides an integrated compact FPP context to study power exhaust solutions on the power plant scale.

It is found that the XPT reduces the electron temperature from 400 eV upstream to 60 eV at the target in a pure-D plasma, for edge parameters relevant to ARC V2A at 500MW fusion power. Beneficial power exhaust properties are linked to very long connection lengths and enhanced neutral radiation around the divertor X-point, key properties of the XPT. Significant divertor performance benefits are observed when the outer leg orientation is more horizontal, with larger toroidal flux expansion detaching several strike-points. Exhaust power and separatrix density scans are performed, and detachment front stability is analysed from the simulation results. Future work will consider comparison with a Super-X divertor and detachment via Ne impurity seeding.

[1] M. Umansky et al 2017 NME 12 918.

[2] C. Theiler et al 2017 NF 57 072008.