Speaker
Description
An understanding of the behaviour of the D or He fuel used in tokamak discharges is necessary for modelling edge and divertor transport. Despite there being well-established models describing the emission from the H-like fuel, poor agreement is found between JET line-of-sight measurements and Collisional-Radiative (CR) models used to predict their line intensities. Lawson et al. (2024) compare measurements of He II intensities with the ADAS and CHEM CR models and find that the modelled Lyman alpha intensity is underestimated (x3-5) compared with the other Lyman intensities. Similar discrepancies are found in the majority of H and D discharges. Although allowance can be made for different temperature regions falling within the spectrometer's line-of-sight, it is nevertheless supposed that the dominant emission for all lines in the Lyman series originates from the same spatial location. However, evidence from H-fuelled discharges suggests different spatial locations for the Lyman alpha emission as opposed to the higher series members and agreement is obtained for the He II measurements when two distinct emission regions are supposed, a higher temperature region corresponding to the ionization front and a low temperature region dominated by recombination.
A long-standing discrepancy between measurements of the divertor radiated power and that predicted by transport simulations has been noted by among others Groth et al. (2013), Jarvinen et al. (2015) and, most recently, by Rees et al. (2026). The simulated radiated powers underestimate the measurements by typically ~x2. Exploratory EDGE2D-EIRENE simulations of a He-fuelled discharge are used to investigate applying constraints to the simulations in order to reproduce the two observed emission regions. The simulations are particularly sensitive to the electron power loss term (Lawson et al., 2018), which includes the losses due to radiation, and additional constraints are applied by varying the magnitude of this term. He II is ideal for this study in that the intensity ratios are reproducible, with near-constant line intensity ratios (Lawson et al., 2024).
Groth M et al. 2013 Nucl. Fusion, 53, 093016
Jarvinen A et al. 2015 J. Nucl. Mater., 463, 135
Lawson K D et al., 2018, EPS conf., Prague
Lawson K D et al., 2024, PPCF, 66, 115001
Rees D et al., 2026, This conference