The dynamics of the ionization processes in an oxygen Z-pinch plasma h
as been numerically studied. Ionization balance equations incorporated
in single-fluid magnetohydrodynamics (MHD) equations were solved. The
focus was on the imploding phase before a shock wave was fully develo
ped. It was shown that the propagation speed of an ionization stage is
larger than the fluid speed. For example, the propagation speed of O
III ionization stage is faster than the fluid speed at the position of
the peak density of O III particles. The larger propagation speeds of
ionization stages than the fluid speed result from the propagation of
Joule heating power. (C) 1997 American Institute of Physics.