  In this work we provide experimental insights into the impact of
plasma-molecule interactions on the target ion flux decrease during divertor
detachment achieved through a core density ramp in the TCV tokamak. Our
improved analysis of the hydrogen Balmer series shows that plasma-molecule
processes are strongly contributing to the Balmer series intensities and
substantially alter the divertor detachment particle balance. We find that
Molecular Activated Recombination (MAR) ion sinks from $H_2^+$ and/or $H^-$ are
a factor $\sim$ 5 larger than Electron-Ion Recombination (EIR) and are a
significant contributor to the observed reduction in the outer divertor ion
target flux. Molecular Activated Ionisation (MAI) may also be significant
during detachment. Plasma-molecule interactions enhance the Balmer line series
emission strongly near the target as detachment proceeds. This indicates
enhancements of the Lyman series, potentially affecting power balance in the
divertor. As those enhancements vary spatially in the divertor and are
different for different transitions, they are expected to result in a
separation of the $Ly\beta$ and $Ly\alpha$ emission regions. This may have
implications for the treatment and diagnosis of divertor opacity. The
demonstrated enhancement of the Balmer series through plasma-molecule processes
potentially poses a challenge to using the Balmer series for understanding and
diagnosing detachment based only on atom-plasma processes.

Plasma Physics