Designing, Testing, and Optimizing the Laser‐cut Foil X‐pinch and Benchmarking it against Wire and Hybrid X‐pinches

Wire X-pinches have been comprehensively studied for nearly four decades as a fast (~1 ns Full-Width Half-Max: FWHM), small (~1\textmu m) X-ray source in pulsed-power experiments. Room for improvement to this array remains though, including reducing variability in source timing, size, quantity, and flux, and the presence of strong electron beam emission post-pinch that tends to doubly expose any acquired radiograph. Many of these limitations can be reduced by optimal mass-matching of the target X to the current driver in use and a reliable cross-point geometry.Addressing these two parameters, we developed a new X-pinch, and tested in on the 200kA, 150ns rise-time GenASIS driver at UC San Diego. This new X is cut from thin metallic foils using a precision laser-cutting facility which can fabricate virtually any cross-sectional mass or crosspoint configuration. The first laser-cut foil X-pinch (LCXP) experiments used Ta, and demonstrated comparable evolution and equal or superior X-ray source parameters to comparably massed W wire X-pinches (WXPs), despite markedly different initial geometry (ie a square or trapezoidal crosspoint cross-section). Subsequent Cu LCXP experiments showed that the X-ray pulse from these targets was confined to a ~2ns period in contrast with the resolvable second pulse of hard X-ray electron beam emission common in WXPs. However, spectroscopic data showed evidence of a beam source co-located with the $\geq$10% solid density, ~1keV hot pinch source.Another promising X-pinch configuration (developed at Cornell University), the hybrid X-pinch (HXP), which consists of two conical electrodes 1-3mm apart bridged by a thin wire or capillary, demonstrated predominantly single source X-pinches and less hard X-ray emission than found in WXPs. To compare all three aforementioned X-pinch configurations–wire, hybrid, and laser-cut foils–we conducted an in-depth performance study of these X’s on the GenASIS driver, representing the first time all three configurations were compared on a single platform. All configurations produced short (~$1ns FWHM), small ($\leq$5\textmu m, both diagnostically limited), soft (Cu L-shell, ~1keV) X-ray sources with comparable peak fluxes, while the thermal K-shell flux increased from hybrid to wire to foil X-pinches. Ultimately, each array possesses benefits and drawbacks which are detailed herein.