Comparative study of recombining He plasmas below 0.1 eV using laser Thomson scattering and spectroscopy in the divertor simulator MAP-II

The recent upgrades of the MAP-II Laser Thomson Scattering (LTS) system and the development of a new Hetero-Tandem Double Monochromator, allowed detectable electron temperatures as low as 0.05 eV and electron densities as low as 10 12 cm - 3 . This enabled the study of He Electron Ion Recombining (EIR) plasmas and the comparison with optical emission spectroscopy for He I Rydberg states in partial local thermal equilibrium (p-LTE). 2 1 P - n 1 D and 2 3 P - n 3 D series with transitions from principal quantum numbers n = 9 – 16 were used for the T e derivation. Results from both Boltzmann plot and Collisional Radiative model fitting are consistent with those from LTS. The very low temperature of 0.06 eV, usually obtained by the Boltzmann plot for He EIR states, is confirmed.