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

Talbot-Lau X-ray Deflectometry (TXD) enables refraction-based imaging for high-energy-density physics (HEDP) experiments, and thus, it has been studied and developed with the goal of diagnosing plasmas relevant to Inertial Confinement and Magnetic Liner Inertial Fusion. X-pinches, known for reliably generating fast (~1 ns), small (~1 µm) x-ray sources, were driven on the compact current driver GenASIS (~200 kA, 150 ns) as a potential backlighter source for TXD. Considering that different X-pinch configurations have characteristic advantages and drawbacks as x-ray generating loads, three distinct copper X-pinch configurations were studied: the wire X-pinch, the hybrid X-pinch, and the laser-cut X-pinch. The Cu K-shell emission from each configuration was characterized and analyzed regarding the specific backlighter requirements for an 8 keV TXD system: spatial and temporal resolution, number of sources, time of emission, spectrum, and reproducibility. Recommendations for future experimental improvements and applications are presented. The electron density of static objects was retrieved from Moiré images obtained through TXD. This allowed to calculate the mass density of static samples within 4% of the expected value for laser-cut X-pinches, which were found to be the optimal X-pinch configuration for TXD due to their high reproducibility, small source size (≤5 µm), short duration (~1 ns FWHM), and up to 10^6 W peak power near 8 keV photon energy. Plasma loads were imaged through TXD for the first-time using laser-cut X-pinch backlighting. Experimental images were compared with simulations from the X-ray Wave-Front Propagation code, demonstrating that TXD can be a powerful x-ray refraction-based diagnostic for dense Z-pinch loads. Future plans for Talbot-Lau Interferometry diagnostics in the pulsed-power environment are described.

Non-Intrusive Measurements of Wave-Induced Flow over Dikes by Means of a Combined Ultrasound Doppler Velocimetry and Videography

The performance of non-intrusive instruments, such as acoustic profilers and cameras, to describe the wave-induced flow processes over maritime dike crest was investigated in experiments carried out at the University of Bologna. Direct and derived measurements from the acoustic probes deployed along the structure crest were discussed in relation to the observed backscatter rates. Image processing was implemented by means of clustering algorithm, in order to detect the free surface during overtopping events and characterize wave front propagation over the dike crest. UVP data were processed to indirectly derive flow depths and overtopping rates and compare them with the direct measurements in order to assess the measurement reliability and discuss their limits. Individual overtopping volume distribution as obtained by UVP data were estimated and compared with well-consolidated formulations, showing a good agreement. Finally, suggestions for an appropriate use of non-intrusive instruments to characterize a shallow, transient and aerated flow were provided, such as the control of the artificial seeding density, the use of a bi-static UVP configuration and adjustments to light exposure.