A novel hydrogenic spectroscopic technique for inferring the role of plasma-molecule interaction on power and particle balance during detached conditions

Abstract

Detachment, an important mechanism for reducing target heat deposition, is achieved through reductions in power, particle and momentum; which are induced through plasma-atom and plasma-molecule interactions. Experimental research in how those reactions precisely contribute to detachment is limited. In this work, we investigate a new spectroscopic technique to utilise Hydrogen Balmer line measurements to 1) disentangle the Balmer line emission from the various plasma-atom and plasma-molecule interactions; and 2) quantify their contributions to ionisation, recombination and radiative power losses. During detachment, the observed $H\alpha$ emission often strongly increases, which could be an indicator for plasma-molecule interactions involving $H_2^{+}$ and/or $H^{-}$. Our analysis technique quantifies the $H\alpha$ emission due to plasma-molecule interactions and uses this to 1) quantify the Balmer line emission contribution due to $H_2^{+}$ and/or $H^{-}$; 2) subsequently estimate its resulting particle sinks/sources and radiative power losses. Its performance is verified using synthetic diagnostic techniques of both detached TCV and MAST-U SOLPS-ITER simulations. Experimental results of this technique on TCV data show a bifurcation occurs between the measured total $H\alpha$ and the atomic estimate of $H\alpha$ emission, indicative of the presence of additional $H\alpha$ due to plasma-molecule interactions with $H_2^{+}$ (and/or $H^{-}$). An example analysis shows that the hydrogenic line series, even $Ly\alpha$ as well as the medium-n Balmer lines can be significantly influenced by plasma-molecule interactions by tens of percent during which significant Molecular Activated Recombination (MAR) is expected.

References in corpus (5)

• Kernel density estimation via diffusion
• Ionisation state, excited populations and emission of impurities in dynamic finite density plasmas. I: The generalised collisional-radiative model for light elements
• An improved understanding of the roles of atomic processes and power balance in divertor target ion current loss during detachment
• Spectroscopic investigations of divertor detachment in TCV
• Novel inferences of ionisation & recombination for particle/power balance during detached discharges using deuterium Balmer line spectroscopy

Cited by in corpus (8)

• Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor
• The role of plasma-molecule interactions on power and particle balance during detachment on the TCV tokamak
• A study of the influence of plasma-molecule interactions on particle balance during detachment
• The role of plasma-atom and molecule interactions on power \& particle balance during detachment on the MAST Upgrade Super-X divertor
• Vibrational excitation and dissociation of deuterium molecule by electron impact
• Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations
• Divertor shaping with neutral baffling as a solution to the tokamak power exhaust challenge
• Multi-Machine Scaling Laws for Fuel and Impurity Puffing Rates Sufficient for Detachment Access: a Systematic Review of Magnetic Confinement Fusion Devices