The role of plasma-atom and molecule interactions on power \& particle balance during detachment on the MAST Upgrade Super-X divertor

Abstract

This paper shows first quantitative analysis of the detachment processes in the MAST Upgrade Super-X divertor (SXD). We identify an unprecedented impact of plasma-molecular interactions involving molecular ions (likely $D_2^{+}$), resulting in strong ion sinks (Molecular Activated Recombination - MAR), leading to a reduction of ion target flux. The MAR ion sinks exceed the divertor ion sources before electron-ion recombination (EIR) starts to occur, suggesting that significant ionisation occurs outside of the divertor chamber. In the EIR region, $T_e\ll 0.2$ eV is observed and MAR remains significant in these deep detached phases. The total ion sink strength demonstrates the capability for particle (ion) exhaust in the Super-X Configuration. Molecular Activated Dissociation (MAD) is the dominant volumetric neutral atom creation process can lead to an electron cooling of 20\% of $P_{SOL}$. The measured total radiative power losses \emph{in the divertor chamber} are consistent with inferred hydrogenic radiative power losses. This suggests that intrinsic divertor impurity radiation, despite the carbon walls, is minor in the divertor chamber. This contrasts previous TCV results, which may be associated with enhanced plasma-neutral interactions and reduced chemical erosion in the detached, tightly baffled SXD. The above observations have also been observed in higher heat flux (narrower SOL width) type I ELMy H-mode discharges. This provides evidence that the characterisation in this paper may be general.

References in corpus (8)

• Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor
• The role of plasma-molecule interactions on power and particle balance during detachment on the TCV tokamak
• Scaling of the scrape-off layer width during inter-ELM H modes on MAST as measured by infrared thermography
• Vibrational excitation and dissociation of deuterium molecule by electron impact
• Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations
• New insights on divertor parallel flows, ExB drifts, and fluctuations from in situ, two-dimensional probe measurement in the Tokamak à Configuration Variable
• Investigation of atomic and molecular rates in plasma-edge simulations through experiment-simulation comparisons
• Initial Fulcher band observations from high resolution spectroscopy in the MAST-U divertor

Cited by in corpus (3)

• Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations
• Divertor shaping with neutral baffling as a solution to the tokamak power exhaust challenge
• Evolution of radiation profiles in a strongly baffled divertor on MAST Upgrade