Ionization and recombination rates for highly ionized titanium ions from time-resolved spectroscopy of tokamak plasmas.

Abstract

The effective ionization and recombination rate coefficients for Ti xvii--xx were obtained by studying the modulation of line emission by sawtooth oscillations in the TEXT tokamak at the University of Texas. Experimental data are matched with the simulation of titanium-ion emission by a one-dimensional (1D) transport code which includes ionization and recombination processes. The rate coefficients were determined for ${T}_{e}$\ensuremath{\approxeq}600--1100 eV and ${N}_{e}$\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. The ionization rates were about 20% higher than values calculated by Lotz's formula. The recombination rates were about 20% less than theoretical values. The uncertainty of ionization and recombination rate coefficients is estimated to be less than 20% and 60%, respectively. The sensitivity of our method to various parameters, i.e., the diffusion coefficient, convective velocity, and electron temperature, is also discussed.