Direct comparison of wire, foil, and hybrid X-pinches on a 200 kA, 150 ns current driver

Abstract

Wire X-pinches (WXPs) have been studied comprehensively as fast (∼1 ns pulse width), small (∼1 μm) x-ray sources, created by twisting two or more fine wires into an “X” to produce a localized region of extreme magnetic pressure at the cross-point. Recently, two alternatives to the traditional WXP have arisen: the hybrid X-pinch (HXP), composed of two conical electrodes bridged by a thin wire or capillary, and the laser-cut foil X-pinch (LCXP), cut from a thin foil using a laser. We present a comparison of copper wire, hybrid, and laser-cut foil X-pinches on a single experimental platform: UC San Diego’s ∼200 kA, 150 ns rise time GenASIS driver. All configurations produced 1–2 ns pulse width, ≤5 μm soft x-ray (Cu L-shell, ∼1 keV) sources (resolutions diagnostically limited) with comparable fluxes. WXP results varied with linear mass and wire count, but consistently showed separate pinch and electron-beam-driven sources. LCXPs produced the brightest (∼1 MW), smallest (≤5 μm) Cu K-shell sources, and spectroscopic data showed both H-like Cu Kα lines indicative of source temperatures ≥2 keV, and cold Kα (∼8050 eV) characteristic of electron beam generated sources, which were not separately resolved on other diagnostics (within 1–2 ns and ≤200 μm). HXPs produced minimal K-shell emission and reliably single, bright, and small L-shell sources after modifications to shape the early current pulse through them. Benefits and drawbacks for each configuration are discussed to provide potential X-pinch users with the information required to choose the configuration best suited to their needs.

Optical diagnostics of laser-produced plasmas

“…In another study, time-stretch imaging was used to record the time lapse of shock wave propagation during a single-shot LPP, enabling its full dynamics to be monitored (Hanzard et al, 2018). Multiple shadowgram/Schlieren images were captured by splitting the beams into four and probing the plasma at various delays by using a regular CMOS digital single-lens reflex (DSLR) camera as the detector (Collins IV et al, 2021). In high-speed laser stroboscopic videography, a high-repetition-rate probe laser in conjunction with a high-speed camera is used for capturing the time sequence of images during a single-shot laser ablation (Tanabe et al, 2015).…”

Wire, hybrid, and laser-cut X-pinches as Talbot–Lau backlighters for electron density diagnostics

“…Recent studies found that x-ray emission from WXP varies with linear mass and wire count and originates from separate pinch (hot-spot) and electronbeam-driven sources, while HXP emission originates from single or co-located sources and is the configuration most sensitive to the driver current profile. In turn, LCXP emission was found to be the brightest and smallest [31]. Most of the X-pinches studied used copper to obtain ∼8 keV K-shell emission, though a few HXPs were tested using Constantan, a high-resistivity Ni-Cu alloy.…”

“…Optimal spacing between conical electrodes was ⩽2.5 mm (shown in figure 3(b)). Further details about distance parameter optimization can be found in a separate publication [31]. • LCXPs machined from 25 and 30 µm thick annealed or hardened temper copper foil with an average cross-point width of ∼25 µm (see figure 3(c)).…”

“…• LCXPs machined from 25 and 30 µm thick annealed or hardened temper copper foil with an average cross-point width of ∼25 µm (see figure 3(c)). The foils were cut using a TRUMPF Trumark 5000 laser workstation with a target design similar to that found in [31,78,79].…”

“…Experiments performed in the multi-terawatt laser (∼10 15−16 W cm −2 ) recently demonstrated increased ∼5-10 µm spatial resolution and experiments on the omega EP laser (∼10 16−17 W cm −2 ) delivered >10 µm spatial resolution. However, backlighter target modification leading to increased spatial resolution has shown to negatively impact signal-to-noise ratio as well as TXD image contrast [31]. A new TXD monochromatic configuration uses a multi-layer mirror to only reflect 8 keV emission.…”