Anisotropy and pulse shaping of radiation emitted from multi-planar wire arrays

Compact double and triple planar wire arrays (DPWA and TPWA) demonstrated the largest resistive energy and power gain, and the highest current scaling among all tested loads at the UNR Zebra generator. Knowledge of the spatial distribution of x-ray radiation from the plasma source is crucial for ICF and radiation physics applications of PWAs [B. Jones et al., PRL, v. 104, 125001 (2010)]. New experiments indicated anisotropic emission from PWAs. Experiments were performed on the UNR Zebra generator with a peak current increased from 0.9 up to 1.7 MA by application of a new load current multiplier (LCM) developed and tested in collaboration with Ecole Polytechnique, France, and Sandia National Laboratories. For SPWAs, the total yield registered orthogonally to the array plane (E⊥) was higher than measured along the plane (E∥) and anisotropy ratio was (E⊥/E∥ < 1.7). For DPWAs and TPWAs, the same ratio was a little less, < 1.25 for DPWAs and up to 1.35 for TPWAs. This can be explained by intense absorption of x-ray radiation in the direction of cold trailing mass plasma collected during implosion along the array plane (for SPWAs) and in a direction perpendicular to the array planes (for DPWAs or TPWAs). Another observation that supports the opacity effects for SPWAs was that the time interval between the current start and the moment when the sub-keV radiation pulse began was found to be greater for registration along the array plane compared to collecting perpendicular to the plane (t∥ > t⊥). The ΔtSPWA was from 3 to 10 ns. However, it was opposite for DPWA (t⊥ > t∥ and Δt DPWA was up to 8 ns). New results were obtained on x-ray pulse shaping from PWAs. Experiments with DPWA with straight and skewed wires and TPWA have shown a different set of pulse shapes (pre-pulses and pulse “steps” on front of sub-keV burst). The results were in qualitative agreement with predictions made using Wire Ablation Dynamic Model. Future directions of research are discussed.