Comparative analysis of K-shell yield of pure aluminum and alloyed Al/Mg wire-array Z-pinches

Multi-keV K-shell radiation is produced in low-to mid-Z w ire-array Z-pinch implosions, and can be used for the research of radiation-material interaction. In this paper we discuss the variation of the K-shell yield of pure aluminum and alloyed Al/Mg wire-array Z-pinch implosions with load parameters. It is shown that the K-shell yield from a pure aluminum wire-array Z-pinch implosion first increases, peaks and then decreases with the increase of load mass for a given generator. Similar to the load mass, there also exists an optimal initial wire-array radius that generates the highest K-shell radiation. The optimal load parameters are determined by the load energy coupling with the generator, the capability of Z-pinch plasmas to emit the K-shell radiation, and the self absorption of K-shell lines. For different generators the optimal load mass should be increased to produce more K-shell yield when the drive current increases. Consequently, the wire-array plasma with optimal load mass is more optically thick, and the absorption of K-shell lines becomes a more important factor that limits the further increase of K-shell yield for a higher drive current generator. It is proved that alloyed Al/Mg wire-arrays may decrease the opacity of K-shell lines and increase the overall K-shell yield remarkably compared to pure aluminum wire-arrays while keeping the total load mass constant. When the mass share of magnesium in alloyed Al/Mg wire-arrays is small, the optical depths of magnesium K-shell lines are much smaller than those of aluminum. Therefore, the increase of the magnesium K-shell yield will exceed the decrease of the aluminum K-shell yield. It is also noted that the K-shell yield should decrease if the mass share of magnesium exceeds a certain point, because of the self strong absorption of magnesium K-shell lines. We will also show that the efficiency of increasing the K-shell yield with alloyed Al/Mg wire-arrays cannot increase indefinitely in the case of optimal load parameters for different generators. The ratio of K-shell yield from an alloyed Al/Mg wire-array to that from a pure aluminum wire-array reaches a limit.