Charge-exchange factor in EBIT spectral analysis

Spectral analysis of an EBIT plasma requires an understanding of the ionization balance. Simulations require accurate atomic data (excitation, ionization, and recombination cross sections) and known operating conditions (electron beam density and energy, and trapped ion temperature). For highly charged ions in an EBIT, charge exchange (CX) recombination is significant despite the relatively low density of neutral ions. Uncertainties of the CX cross sections combined with the limited knowledge of the experimental parameters (neutral density, relative ion velocity) constrain the models of spectral emission. To combine the unknown factors into one free parameter, we introduce a charge exchange factor that can be accurately determined experimentally using measured line intensity ratios and theoretical cross sections. Using measured Fe spectra at multiple electron beam energies (9.21 kV x 18 kV), the charge exchange factor was determined in a measurement at NIST. The factor was used in our collisional-radiative (CR) model* to produce simulated spectra and line intensity ratios. The agreement demonstrates the usefulness of this approach for spectral modeling.