Measurement of ionization rates of Ti ix, Ne vi, Ne vii, and O vi

The effective ionization rates of Ti ix, Ne vi, Ne vii, and O vi have been measured with the use of the plasma spectroscopy method in a $\theta$ pinch discharge at an electron temperature (50-60 eV) much below their ionization threshold and at an electron density of (≃ 2-3)×${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$. A theoretical analysis of the effective ionization rates showed that excitation ionization is a major contributing process. Theoretical values are in reasonable agreement with experiment.