Investigation of K-shell emission from moderate-Z, low-eta (-velocity), Z-pinch implosions

Because of the large amount of kinetic energy and mass needed for efficient production of K-shell emission from moderate atomic number z-pinch plasmas (Z>22), moderate Z experiments performed in the near future will likely take place at relatively low implosion velocities or low-eta values, where eta is defined as the ratio of lire maximum kinetic energy per ion generated prior to stagnation to the minimum energy per ion, E(min) needed to instantly heat and to ionize a plasma into the K shell upon stagnation of the pinch. Since there has been no systematic theoretical or experimental investigations of K-shell yield scaling with mass and atomic number in the low-eta regime eta similar to 1-3, in anticipation of such future experiments, we report on the results of our theoretical investigation into this regime. in particular aluminum, argon, titanium, and krypton plasmas were studied using a 1D radiation hydrodynamics model that uses enhanced transport coefficients to phenomenologically attain the stagnation conditions of experimental z-pinches, The results of this study have identified the following important effects: low-eta plasmas remain in an inefficient mass(2) (or current(4)) scaling regime at much higher masses than predicted by our earlier work,(1,2) which was based on eta > 3.7 calculations. Thus, more energy than predicted by the earlier scaling laws will apparently be needed to obtain significant amounts of, for example, krypton K-shell emission. In addition; lags in ionization times become important increasingly with the Z of the plasma and adversely affect K-shell emission. The physics responsible for these time dependent effects and how they will influence the design of future experiments are discussed.