Energy balance and ionization dynamics in an imploding Z-pinch plasma

Summary form only given. The results of our spectroscopic study of the energy balance history during the implosion phase of a 300 kA, 1 /spl mu/s gas-puff z-pinch plasma are presented. Using the measured spectral line profiles and intensities of singly- to five-fold ionized oxygen ions we obtained the time-dependent radial distributions of the magnetic field, electron density, electron temperature, radial velocity, and the mean ion charge. These parameters were used for determining as a function of time and radius all the terms of the momentum and energy equations as used in a standard 1-D MHD modelling scheme. For the analysis we follow the evolution of the plasma parameters within a few mass elements. In detail, the Joule heating of electrons is calculated using the current density obtained from the magnetic-field measurements, and the electrical conductivity shown to be classical (Spitzer). The plasma compressional heating is calculated using the radial velocity gradient and the total (p/sub e/+p/sub i/) thermal pressure, which is obtained from the measured electron temperature and density, the measured mean ion charge, and the ion temperature, estimated using the calculated electron-ion energy transfer rate. The electron heat flux is calculated using the measured electron temperature gradient. The electron energy losses due to excitation, radiation, and ionization, are determined using detailed collisional-radiative calculations. Analysis of the energy balance and the plasma acceleration shows that the previously observed propagation of the ionization front, and the resulting ion charge-state distribution across the plasma shell are consistent with the heating rates calculated using the experimentally determined MHD parameters.