3 research outputs found
The role of plasma-atom and molecule interactions on power \& particle balance during detachment on the MAST Upgrade Super-X divertor
First quantitative analysis of the detachment processes in the MAST Upgrade
Super-X divertor show an unprecedented impact of plasma-molecular interactions
involving molecular ions (likely ), resulting in strong ion sinks,
leading to a reduction of ion target flux. This starts to occur as the
ionisation source detaches from the target, leading to a build-up of molecules
below the ionisation source who get excited, resulting in Molecular Activated
Recombination (MAR) and Dissociation (MAD). The particle sinks in the divertor
chamber exceed the ion sources in the middle of the detached operational regime
before electron-ion recombination (EIR) starts to occur, demonstrating the
strong capabilities for particle exhaust in the Super-X Configuration. MAD is
the dominant volumetric neutral atom creation mechanism and results in
significant power losses. This, combined with electron-impact excitation
preceding ionisation, are the dominant power loss mechanisms in the divertor
chamber. As the plasma becomes more deeply detached, EIR starts to occur and
electron temperatures below 0.2 eV are achieved. Even at such low electron
temperature conditions, MAR is observed to be an important ion sink mechanism,
which suggests the presence of highly vibrationally excited molecules in the
cold detached regime. The total radiative power loss is consistent with
extrapolations of spectroscopic inferences to hydrogenic radiative power
losses, which suggests that intrinsic impurity radiation, despite the carbon
walls, is minor. These observations are observed in Ohmic L-mode, ELM-free
H-mode and type I ELMy H-mode discharges
The role of plasma–atom and molecule interactions on power & particle balance during detachment on the MAST Upgrade Super-X divertor
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 D2+ ), 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, Te≪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 is the dominant volumetric neutral atom creation process can lead to an electron cooling of 20% of PSOL . The measured total radiative power losses 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