Trends in plasma conditions inferred from an analysis of x-ray data from high wire-number, Z-pinch load implosions

An analysis of x-ray data from two series of Z-pinch shots taken on the sho rt current-risetime Saturn accelerator at Sandia National Laboratories [Pro ceedings of 6th International IEEE Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (IEEE, New York, 1987), p. 310] is presented. In one series, the array radius was held constant and the arr ay mass was varied; in the other series, the array mass was held constant a nd its radius varied. In both sets of experiments, large wire-number loads (N greater than or equal to 93) of aluminum were used in contrast to earlie r small wire-number aluminum array experiments on Saturn where N less than or equal to 42. Average electron temperatures and ion densities were inferr ed from the data. In addition, from the measured size of the emission regio n of K-shell x rays and from the inferred ion density, a fraction of the to tal array mass that participated in the K-shell emission was inferred and f ound to be directly correlated to the K-shell yields that were measured. Th is paper also demonstrates that the yields varied as a function of array ma ss and radius in much closer agreement with predictions [J. Appl. Phys. 67, 1725 (1990)] than had been observed in the earlier small wire-number exper iments. Thus, a serious misperception that the reason for the early disagre ement was in the calculations and not in the experiments is corrected. Thes e predictions were made using one-dimensional (1D) magnetohydrodynamics cal culations. The density and temperature trends inferred from the data analys is are well-behaved and consistent with the 1D calculations. This data anal ysis confirms the importance of achieving uniform plasma initial conditions and implosion symmetry when comparing computer code calculations with expe riment. When the wire number of an array load is increased, a more uniform shell of plasma is calculated initially as the wires explode and, as the pl asma stagnates on axis, the x-ray powers and yields are found experimentall y to approach the powers and yields predicted by 1D calculations. (C) 2001 American Institute of Physics.