Resonant excitation channels in the 3[Formula Presented]-3[Formula Presented]4s and 3[Formula Presented]-3[Formula Presented]4p transitions of nickel-like [Formula Presented] and [Formula Presented]

At energies below the threshold for direct electron impact excitation, resonant excitations can make a significant contribution to the total excitation rate of a given energy level. In this paper, the rates of resonant excitation into the levels of the 3[Formula Presented]4s and 3[Formula Presented]4p configurations of [Formula Presented] have been calculated using a fully relativistic, multiconfiguration atomic structure code and detailed accounting of energy levels. By including the effects of resonant excitations in collisional-radiative models for the spectrum of Ni I–like [Formula Presented] and (by isoelectronic scaling) [Formula Presented], the ratio of the emissivity of the 3[Formula Presented]-4[Formula Presented]4s E2 transitions to the emissivity of the 3[Formula Presented]-3[Formula Presented]4p E1 transitions is greatly enhanced, and sensitivity to electron temperature in the ratio is introduced. This ratio is density sensitive for [Formula Presented]≥[Formula Presented] [Formula Presented], and therefore, given knowledge of either local temperature or density conditions, the E2-E1 ratio can serve as a diagnostic for local conditions in magnetically confined fusion plasmas. The current work demonstrates the need to include resonant excitations in collisional-radiative models of the soft x-ray emission of nickel-like ions. Good agreement is found between measurements of E1 and E2 line brightness ratios made in a tokamak plasma, and the predictions of collisional-radiative models in the present work.