A study of the VUV emission from highly ionized krypton in a theta pinch plasma

The ionization rates of Kr(IX), (X), (XI), and (XII) have been measured using a fast 60-kV-60kJ theta pinch as a plasma source. The line emission from each ion stage has been identified and the time evolution observed. A coupled set of rate equations was used along with time- and space-resolved measurements of the electron density and temperature to model the plasma light emission. The ionization rates of Kunze were adjusted by multiplying the rate for each ion stage with a constant until the peak intensity of the calculated emission agreed with the time of the observed peak intensity. The constants required for best fit were 2.5, 0.15, 3.0, and 2.0 for Kr(IX), (X), (XI), and (XII), respectively. Two successive ionization stages, Kr(X) and Kr(XI), have shown the same time dependence and possible reasons for this observation are discussed. During the course of modeling the light emission, we have also found that the rate for the excitation from the 3dⁿ to the 3p⁵3dⁿ⁺¹ level in Kr(X) (n=9) and Kr(XI) (n=8) is a factor of 5 lower than predicted by the van Regemorter excitation rate equation.