  This experimental study presents an in-depth investigation of the performance
of the MAST-U Super-X divertor during NBI-heated operation (up to 2.5 MW)
focussing on volumetric ion sources and sinks as well as power losses during
detachment.
  The particle balance and power loss analysis revealed the crucial role of
Molecular Activated Recombination and Dissociation (MAR and MAD) ion sinks in
divertor particle and power balance, which remain pronounced in the change from
ohmic to higher power (NBI heated) L-mode conditions. The importance of MAR and
MAD remains with double the absorbed NBI heating. MAD results in significant
power dissipation (up to $\sim 20 \%$ of $P_{SOL}$), mostly in the cold ($T_e <
5$ eV) detached region. Theoretical and experimental evidence is found for the
potential contribution of $D^-$ to MAR and MAD, which warrants further study.
  These results suggest that MAR and MAD can be relevant in higher power
conditions than the ohmic conditions studied previously. Post-processing
reactor-scale simulations shows that MAR and MAD can play a significant role in
divertor physics and synthetic diagnostic signals of reactor-scale devices,
which are currently underestimated in exhaust simulations. This raises
implications for the accuracy of reactor-scale divertor simulations of
particularly tightly baffled (alternative) divertor configurations.
