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

TL;DR

This paper introduces a novel spectroscopic analysis method for deuterium Balmer lines to measure particle and power balances in divertor plasmas, enhancing understanding of detachment physics.

Contribution

It develops a new technique using Balmer line ratios and Monte Carlo error analysis to separately quantify ionisation and recombination contributions during divertor detachment.

Findings

Successfully measured particle and power balance during detachment on TCV.

Validated the method against synthetic diagnostics from SOLPS simulations.

Provided detailed insights into ion flux control during divertor detachment.

Abstract

The physics of divertor detachment is determined by divertor power, particle and momentum balance. This work provides a novel analysis technique of the Balmer line series to obtain a full particle/power balance measurement of the divertor. This supplies new information to understand what controls the divertor target ion flux during detachment. Atomic deuterium excitation emission is separated from recombination quantitatively using Balmer series line ratios. This enables analysing those two components individually, providing ionisation/recombination source/sinks and hydrogenic power loss measurements. 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. Power/particle balance measurements have been obtained during attached and detached conditions on the TCV tokamak.