Characterization of detachment inferred from the Balmer line ratios in JET-ILW low-confinement mode plasmas

Spectroscopic measurements of the hydrogenic Balmer-α and Balmer-γ line emission in JET-ILW low-confinement mode (L-mode) deuterium plasmas are used to assess the onset of volume recombination in the low-field side (LFS) divertor. The evolution of the EDGE2D-EIRENE predicted Balmer-γ to Balmer-α emission ratio from low-recycling to detached conditions is in qualitative agreement with the measured ratio. In low-recycling conditions the EDGE2D-EIRENE predicted line-emission is within 30% of measured emission, in high-recycling within 20%t, and in detached conditions lower by a factor of 2.5.. Authors: Rikala, Vesa-Pekka [Aalto Univ. (Finland)] (ORCID:0000000319577267); Groth, M. [Aalto Univ. (Finland)] (ORCID:0000000173971586); Meigs, A. G. [UK Atomic Energy Authority (UKAEA), Culham (United Kingdom)] (ORCID:000000028071864X); Reiter, D. [Heinrich Heine Univ. (Germany)] (ORCID:0000000156357103); Lomanowski, B. [UK Atomic Energy Authority (UKAEA), Culham (United Kingdom); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000322262004). DOE Contract: AC05-00OR22725. Subjects: Divertor visible spectroscopy; EDGE2D; EIRENE; Fusion; Scrape-off layer