On the Ionization Equilibrium in High-temperature Plasmas

A comparison is made between measured and calculated distribution of ionization stages in high-temperature low- (Tokamak) and high-density (laser produced) plasmas. The relative abundances of ionization species were derived from the dielectronic satellite spectra of Fe XXV-XVIII in the region λ = 1.85-1.95 Å. New calculations for ionization balance included effects of autoionization accompanied by excitation of doubly-excited states of recombining ion and density-dependence of the dielectronic recombination rate were carried out. The results differ considerably from those of previous calculations which took into account these effects (Jacobs et al. [25]) as well as earlier ones made by Jordan [19]. There is a satisfactory agreement between the experimental ion concentration measured in laser plasmas and that predicted for the electron temperature T e = 1.3 × 10 7 K, ionization temperature T z = 7.6 × 10 6 K and density N e ≈ 10 21-22 cm -1 ; transient or "quasi-steady-state" conditions are observed ( T e ≠ T z ). In the low-density Tokamak plasma obtained by Hill et al. [5] an ionization equilibrium was found to exist at the ionization temperature T z = T e .