The Helium-like-resonance intercombination and forbidden lines (ls21S−ls2p 1P, ls21S−ls2s 3P, ls21S−ls2s 3S respectively) can be observed from hot, low density plasmas such as coronal or tokamak plasmas. They can be used either to measure the electron temperature from the ratio of their intensity to that of the corresponding satellite lines (1s2nℓ′ − ls2ℓnℓ′) as described by Gabriel (1972) or directly as a density diagnostic (Gabriel and Jordan, 1972). The soft X-ray spectra obtained from these plasmas have been observed from space satellite experiments such as the Solar Maximum Mission (Acton et al., 1980), Hinotori (Tanaka et al., 1982) and P78–1 (Doschek et al., 1982) or from tokamaks such as PDX, PLT (Princeton, USA), TFR (Fontenay-aux-Roses, France). The analysis of some of these spectra, for example, Mg XI (Faucher et al., 1983), Ti XXI (Bely-Dubau et al., 1982b) and Ca XIX (Bely-Dubau et al., 1982a, Jordan and Veck 1982) show that these diagnostics are sensitive to the accuracy of the atomic data.and demonstrate the need for improved calculations of the excitation rates for the He-like ions.
Most Intense X-Ray Lines of the Helium Isoelectronic Sequence for Plasmas Diagnostic