Novel inferences of ionisation & recombination for particle/power balance during detached discharges using deuterium Balmer line spectroscopy.

The process of divertor detachment, whereby particle fluxes to divertor surfaces are strongly reduced, is required to reduce heat loading and erosion in a magnetic fusion reactor. The magnitude and time dependence of ions reaching the target are determined by a complex set of constraints based on atomic physics (ionization and recombination), power and particle balance. This work is aimed at supplying more and better information to fully characterize and understand what controls the divertor target ion flux. Balmer series line ratios are utilized to quantitatively separate atomic deuterium excitation from recombination emission. This enabled the new capability to analyse each of those two components individually, providing ionisation/recombination source/sinks and hydrogenic power loss measurements during attached and detached conditions on the TCV tokamak. Probabilistic Monte Carlo techniques were employed to obtain full error propagation - eventually resulting in probability density functions for each output variable. Both local and overall particle and power balance in the divertor are then obtained. These techniques and their assumptions have been verified by comparing the analysed synthetic diagnostic ‘measurements’ obtained from SOLPS simulation results for the same discharge.