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Plasma flow control in the ablation and implosion phases in nested cylindrical and star wire array Z-pinches
AdvisorIvanov, Vladimir V.
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Wire array Z-pinches are the most powerful laboratory x-ray sources, and the optimization of the x-ray radiation output requires the understanding of diverse phenomena. During the wire array implosion in such arrays, the j×B forces ablate plasma from the wires to the center, before the whole array mass implodes. We studied the ablation and implosion dynamics in nested cylindrical and star wire array Z-pinches. The two implosion modes of nested arrays were simulated by Al star wire arrays with "gates". Arrays with regular-length gate wires imploded in the "nontransparent regime". Arrays with long, higher-Z gate wires imploded in the "transparent" regime. A two-frame end-on UV laser probing diagnostics was developed for the Zebra generator.Modified nested cylindrical arrays, called closely spaced arrays, were designed to implode without a precursor. Low-wire number arrays imploded accordingly. Precursor plasma was observed in higher wire-number arrays, despite outward j×B forces on the inner wires. The Al K-shell yield was highest for low wire-number nested arrays, which also imploded earlier. The presence of precursor in star wire arrays was determined by the direction of the j×B forces. Star wire array pairs were designed such that precursor and non-precursor arrays would have minimal differences. The presence of precursor decreased the x-ray yield parameters by 3-15%. Plasma flow control was achieved in these loads by varying the array configuration.Radiative properties of multicomponent Z-pinches and laser produced plasmas were studied. When high-Z element (W, Au) was mixed with Al plasma in a wire array, a decrease of the electron temperature was observed. The cooling effect was not present in laser-produced Al-Au plasmas, which may be explained by different heating mechanisms.