Effect of Yacora evaluated molecular rates on SOLPS-ITERsimulations

The production of D2+ results in plasma-molecular interactions such as MAR and MAD

[1, 2, 3]. MAR results in recombination of D+ which lowers the ion target flux and MAD is a

means of molecular dissociation; These reactions form excited D which result in radiative

losses, ultimately lowering the plasma temperature [1, 3]. After detachment onset, the plasma

temperature near the target drops to low levels where electron impact ionisation of D2 begins

to reduce. In these conditions molecular charge exchange becomes the main source of D2+ [2].

SOLPS-ITER does not replicate the levels of MAR, and MAD seen experimentally on MAST

Upgrade and TCV [1, 3]. This originates from the AMJUEL molecular effective charge

exchange rate coefficient. Which contains inaccuracies below 2 eV [4, 5, 6, 7].

A molecular rate coefficient dataset has been calculated as input for EIRENE based on the

vibrationally-resolved Yacora ground state model (Yacora-H2(X1, v)) which uses the Yacora

ODE solver [8, 9]. This dataset was applied to an isolated divertor leg geometry in

SOLPS-ITER with MAST Upgrade L-mode Super-X conditions and compared to an AMJUEL

reference [10]. Below Te = 1 eV , the novel molecular charge exchange effective rate coefficient

increases the levels of D2+. In the highest density case, MAR and MAD increases by a factor of

∼ 4 and ∼ 2 respectively. This results in stronger ion target flux roll-over, and larger power

dissipation during detachment that are qualitatively in better agreement with trends on

MAST Upgrade and TCV [1, 3].