Estimation of 2D distributions of electron density and temperature in the JET divertor from tomographic reconstructions of deuterium Balmer line emission

Estimates for 2D distributions of electron density, n_e, and temperature, T_e, have been obtained using reflection-corrected tomographic reconstructions of deuterium Balmer line emission in the JET divertor. The solutions are obtained by a two-dimensional Monte Carlo optimization model, based on intensity ratios of the Balmer D_α, D_γ and D_ε emission and the ADAS photon emission coefficients with additional constraints provided by line-integrated spectroscopic measurements of n_e and T_e. Synthetic benchmarks utilizing EDGE2D-EIRENE simulation outputs yield reproduction of reference n_e and T_e distributions within 25% with statistical error estimates of 5–15%. Experimental analysis of an L-mode n_e ramp shows extension and movement of the outer divertor high-n_e region with n_e,div up to 1.5 × 10²⁰ m⁻³ from the outer strike point to above the X-point and decrease of the divertor T_e to the range of 0.5–1.0 eV within 25% agreement with the line-integrated measurements. Comparison between the local estimates and their corresponding line integrals suggests underestimation of n_e and T_e by up to 75% and 50%, respectively, due to the geometric effects of line integration.