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Mesoscale imperfections, such as pores and voids, can strongly modify the properties and the mechanical response of materials under extreme conditions. Tracking the material response and microstructure evolution during void collapse is crucial for understanding its performance. In particular, imperfections in the ablator materials, such as voids, can limit the efficiency of the fusion reaction and ultimately hinder ignition. To characterize how voids influence the response of materials during dynamic loading and seed hydrodynamic instabilities, we have developed a tailored fabrication procedure for designer targets with voids at specific locations. Our procedure uses SU-8 as a proxy for the ablator materials and hollow silica microspheres as a proxy for voids and pores. By using photolithography to design the targets’ geometry, we demonstrate precise and highly reproducible placement of a single void within the sample, which is key for a detailed understanding of its behavior under shock compression. This fabrication technique will benefit high-repetition rate experiments at x-ray and laser facilities. Insight from shock compression experiments will provide benchmarks for the next generation of microphysics modeling. 

Inertial confinement fusion (ICF) holds increasing promise as a potential source of abundant, clean energy, but has been impeded by defects such as micro-voids in the ablator layer of the fuel capsules. It is critical to understand how these micro-voids interact with the laser-driven shock waves that compress the fuel pellet. At the Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS), we utilized an x-ray pulse train with ns separation, an x-ray microscope, and an ultrafast x-ray imaging (UXI) detector to image shock wave interactions with micro-voids. To minimize the high- and low-frequency variations of the captured images, we incorporated principal component analysis (PCA) and image alignment for flat-field correction. After applying these techniques we generated phase and attenuation maps from a 2D hydrodynamic radiation code (xRAGE), which were used to simulate XPCI images that we qualitatively compare with experimental images, providing a one-to-one comparison for benchmarking material performance. Moreover, we implement a transport-of-intensity (TIE) based method to obtain the average projected mass density (areal density) of our experimental images, yielding insight into how defect-bearing ablator materials alter microstructural feature evolution, material compression, and shock wave propagation on ICF-relevant time scales. 

Abstract Bed material abrasion is a major control on the partitioning of basin‐scale sediment fluxes between coarse and fine material. While abrasion is traditionally treated as an exponential function of transport distance and a lithology‐specific abrasion coefficient, experimental studies have demonstrated greater complexity in the abrasion process: the rate of abrasion varies with clast angularity, transport rate, and grain size. Yet, few studies have attempted to assess the importance of these complexities in a field setting. Here, we develop a new method for rapidly quantifying baseline abrasion rate in the field via Schmidt Hammer Rock Strength. We use this method, along with measurements of gravel bar lithology, to quantify abrasion in the Suiattle River, a basin in the North Cascades of Washington State in which sediment supply to the channel is dominated by recurrent debris flows from a tributary draining Glacier Peak stratovolcano. Rapid downstream strengthening of river bar sediment and a preferential loss of weak, low‐density vesicular volcanic clasts relative to non‐vesicular ones suggest that abrasion is extremely effective in this system. The standard exponential model for downstream abrasion, using single‐lithology abrasion rates fails to reproduce observed downstream patterns in lithology and clast strength. Incorporating heterogeneity in source material strength as well as transport rate‐dependent abrasion largely resolves this failure. Further work is needed to develop a comprehensive quantitative framework for the dependence of bed material abrasion on grain size and transport rate. 

Abstract Profound effects of episodic megafloods (≥10⁶ m³/s) have been observed on Earth and Mars. Quaternary megafloods sourced from valley‐blocking glaciers on the Tibetan Plateau likely play an important role in the geomorphic evolution of the Yarlung‐Tsangpo Gorge and mountain landscape of the eastern Himalaya. We use the first 2D numerical simulation of a megaflood sourced from a reconstructed 81 km³Tibetan lake to analyze flood hydraulics and examine the erosional and depositional potential of megafloods in mountain landscapes. The simulated flood has a duration >60 hr and a peak discharge of 3.1 × 10⁶ m³/s. We find that the extent of inundated features like terraces, narrow valley sections, tight meander bends, and overtopped ridges influences locations of observed maximum depth (370 m), speed (76 m/s), and bed shear stress (>100 kPa), creating dynamic patterns of erosive potential. Consequently, it is difficult to predict local (≤1 km) patterns of megaflood erosional potential from either unit stream power or flood power from smaller magnitude outburst floods. However, both are useful when predicting regional (≥25 km) order‐of‐magnitude shifts in megaflood flood power. Portions of the flood domain downstream of the Gorge experience lower bed shear stresses and flood power <5 kW/m², indicating potential for significant deposition. We suggest widespread deposition of boulders within the modern channel and fine‐grained particles on hillslopes during a megaflood likely impedes subsequent erosion and affects channel width and longitudinal form throughout the flood pathway. Our findings show the legacy of megaflooding in mountainous terrain includes both extensive erosion and deposition. 

Abstract Conservation funding is currently limited; cost‐effective conservation solutions are essential. We suggest that the thousands of field stations worldwide can play key roles at the frontline of biodiversity conservation and have high intrinsic value. We assessed field stations’ conservation return on investment and explored the impact of COVID‐19. We surveyed leaders of field stations across tropical regions that host primate research; 157 field stations in 56 countries responded. Respondents reported improved habitat quality and reduced hunting rates at over 80% of field stations and lower operational costs per km²than protected areas, yet half of those surveyed have less funding now than in 2019. Spatial analyses support field station presence as reducing deforestation. These “earth observatories” provide a high return on investment; we advocate for increased support of field station programs and for governments to support their vital conservation efforts by investing accordingly.