Increased kilo-electron-volt x-ray yields from<i>Z</i>-pinch plasmas by mixing elements of similar atomic numbers

Abstract

Magnesium-coated aluminum wire array Z pinch plasmas have been tested on a 4-MA, 6-TW pulsed electrical generator. A mixture of 80% aluminum and 20% magnesium is observed to maximize the radiated kilovolt x-ray yield at \ensuremath{\ge}50 kJ, which is 50% higher than that obtained with pure aluminum. Spectroscopic analysis and collisional radiative equilbrium models with radiation transport are employed to show that the aluminum-magnesium mixture reduces the opacity of the strongest emission lines, thus increasing the yield by increasing the probability of photon escape. Furthermore, the spectroscopic data also point to the presence of a strong temperature gradient in the pinched plasma that results in the outer magnesium coating of the wires having a higher electron temperature in the pinch. This temperature difference also plays a role in enhancing the kilovolt x-ray yield. The observation of a higher magnesium electron temperature offers evidence that the magnesium reaches the axis first, forming a core that is compressed and heated by the imploding mass of aluminum. Since the emissions from the core are not absorbed by the outer aluminum, the yields are increased. By comparison, aluminum-magnesium alloys imploded on a different but similar generator do not show a temperature difference.