Studies of new closed and open configurations of multi-planar wire arrays with straight and skewed wires and opacity effects observations at unr 1.4 MA zebra generator

Abstract

Experiments with different Z-pinch loads were performed on 1.4 MA, 100 ns Zebra generator at UNR. The program emphasized investigation of plasma formation, implosion and radiation features as a function of the load configuration: compact multi-planar and cylindrical wire arrays. The multi-planar wire arrays (PWA) were studied in open and closed configuration with Al, stainless steel, Cu, brass, Mo and W wires. In open configurations, for single, double, and triple PWAs, wire rows are parallel to each other and there is magnetic field inside the array from the beginning of the discharge. A new closed configuration, Prism-like triangle PWA, eliminates the global magnetic field inside (as cylindrical arrays) ahead of the plasma flow. Prism-like PWAs (that are not equal to compact cylindrical array) show high flexibility in control of implosion dynamics and precursor formation by switching of wire materials and changing mass ablation rates in prism rows and corners. The spectra modeling, MHD and WADM codes have been used for implosion and stagnation parameters simulation. Electron temperature and density in multiple bright spots reached ∼1.4 keV and ∼5×1021 cm−3, respectively. With current rise from 0.8 up to 1.3 MA, opacity effects became more pronounced, which may limit x-ray yields from PWA and especially from CCWA loads: much lower peak current yields scaling for CCWAs compared with PWAs; appearance of absorption lines in x-ray spectra, and anisotropy of sub-keV emission from SPWAs. The DPWA was found to be the best x-ray radiator at 1 MA tested at Zebra: it is characterized by combination of larger resistive energy and power gain (25 kJ and 1 TW), small mm-scale size, the possibility of radiation pulse shaping, and easy diagnostics access to plasmas. These characteristics may even be improved by application of a new tested load: DPWA with skewed wires. In this load, an initial axial magnetic filed is created that might mitigate the magneto-RT instabilities and provide more effective X-ray generation. The experimental results are summarized and discussed.