K-SHELL RADIATION PHYSICS IN THE ULTRAHIGH OPTICAL DEPTH PINCHES OF THE Z-GENERATOR

Al: Mg alloy wire arrays of mass loads 1.3-3.6 mg/cm have been implode d with peak currents of 19 MA on the 60 TW Z generator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories . The large mass loads have resulted in the highest K-shell x-ray line optical depths (similar to 10(3)) produced to date in Z-pinches. Anal ysis of the time-resolved spectrum of a 2.1 mg/cm shot near the time o f peak compression has yielded a temperature-density profile of the pi nch that approximately reproduces all features of the x-ray data excep t the continuum above 5 keV, which is underpredicted. The Ly alpha/He for Al is shown to be enhanced relative to that alpha ratio of Mg by t wo mechanisms: photopumped ladder ionization and absorption of the Al He-like line in a cool outer halo. This analysis and comparisons to so me Ti shots demonstrates that the K-shell yield of Al is significantly reduced by line and continuum self-absorption, but that of Ti is not. (C) 1998 American Institute of Physics. [S1070-664X(98)05012-5].