ALBERT

Description: We have developed a high-current laser ion source for induction accelerators. A copper target was irradiated by a frequency-quadrupled Nd:YAG laser (266 nm) with relatively low intensities of 10 8 W/cm 2 . The laser-produced plasma supplied a large number of Cu + ions (∼10 12 ions/pulse) during several microseconds. Emission spectra of the plasma were observed and the calculated electron temperature was about 1 eV. An induction voltage adder extracted high-current ion beams over 0.5 A/cm 2 from a plasma-prefilled gap. The normalized beam emittance measured by a pepper-pot method was smaller than 1 π mm mrad.

Description: We demonstrate a novel plasma device for magnetic reconnection, driven by Gekko XII lasers irradiating a double-turn Helmholtz capacitor-coil target. Optical probing revealed an accumulated plasma plume near the magnetic reconnection outflow. The background electron density and magnetic field were measured to be approximately 10 18  cm −3 and 60 T by using Nomarski interferometry and the Faraday effect, respectively. In contrast with experiments on magnetic reconnection constructed by the Biermann battery effect, which produced high beta values, our beta value was much lower than one, which greatly extends the parameter regime of laser-driven magnetic reconnection and reveals its potential in astrophysical plasma applications.

Description: Geomagnetically induced currents (GICs) caused by interplanetary shocks represent a serious space weather threat to modern technological infrastructure. The arrival of interplanetary shocks drives magnetosphere and ionosphere currents systems, which then induce electric currents at ground level. The impact of these currents at high latitudes has been extensively researched, but the magnetic equator has been largely overlooked. In this paper, we investigate the potential effects of interplanetary shocks on the equatorial region and demonstrate that their magnetic signature is amplified by the equatorial electrojet. This local amplification substantially increases the region's susceptibility to GICs. Importantly, this result applies to both geomagnetic storms and quiet periods, and thus represents a paradigm shift in our understanding of adverse space weather impacts on technological infrastructure.

Description: Scandium trifluoride (ScF 3 ), adopting a cubic ReO 3 -type structure at ambient pressure, undergoes a pronounced negative thermal expansion (NTE) over a wide range of temperatures (10 K–1100 K). Here, we report the size effects on the NTE properties of ScF 3 . The magnitude of NTE is reduced with diminishing the crystal size. As revealed by the specific heat measurement, the low-energy phonon vibrations which account for the NTE behavior are stiffened as the crystal size decreases. With decreasing the crystal size, the peaks in high-energy X-ray pair distribution function (PDF) become broad, which cannot be illuminated by local symmetry breaking. Instead, the broadened PDF peaks are strongly indicative of enhanced atomic displacements which are suggested to be responsible for the stiffening of NTE-related lattice vibrations. The present study suggests that the NTE properties of ReO 3 -type and other open-framework materials can be effectively adjusted by controlling the crystal size.

Description: Aerosol properties above clouds have been retrieved over the South East Atlantic Ocean during the fire season 2006 using satellite observations from POLDER (Polarization and Directionality of Earth Reflectances). From June to October, POLDER has observed a mean Above-Cloud Aerosol Optical Thickness (ACAOT) of 0.28 and a mean Above-Clouds Single Scattering Albedo (ACSSA) of 0.87 at 550 nm. These results have been used to evaluate the simulation of aerosols above clouds in 5 AeroCom (Aerosol Comparisons between Observations and Models) models (GOCART, HadGEM3, ECHAM5-HAM2, OsloCTM2 and SPRINTARS). Most models do not reproduce the observed large aerosol load episodes. The comparison highlights the importance of the injection height and the vertical transport parameterizations to simulate the large ACAOT observed by POLDER. Furthermore, POLDER ACSSA is best reproduced by models with a high imaginary part of black carbon refractive index, in accordance with recent recommendations.

Description: Aperture alignment is crucial for the diagnosis of neutron imaging because it has significant impact on the coding imaging and the understanding of the neutron source. In our previous studies on the neutron imaging system with coded aperture for large field of view, “residual watermark,” certain extra information that overlies reconstructed image and has nothing to do with the source is discovered if the peak normalization is employed in genetic algorithms (GA) to reconstruct the source image. Some studies on basic properties of residual watermark indicate that the residual watermark can characterize coded aperture and can thus be used to determine the location of coded aperture relative to the system axis. In this paper, we have further analyzed the essential conditions for the existence of residual watermark and the requirements of the reconstruction algorithm for the emergence of residual watermark. A gamma coded imaging experiment has been performed to verify the existence of residual watermark. Based on the residual watermark, a correction method for the aperture misalignment has been studied. A multiple linear regression model of the position of coded aperture axis, the position of residual watermark center, and the gray barycenter of neutron source with twenty training samples has been set up. Using the regression model and verification samples, we have found the position of the coded aperture axis relative to the system axis with an accuracy of approximately 20 μ m. Conclusively, a novel approach has been established to correct the coded aperture misalignment for fast neutron coded imaging.

Description: A simple scheme to produce strong magnetic fields due to cold electron flow in an open-ended coil heated by high power laser pulses is proposed. It differs from previous generation of magnetic fields driven by fast electron current in a capacitor-coil target [S. Fujioka et al ., Sci. Rep. 3 , 1170 (2013)]. The fields in our experiments are measured by B-dot detectors and proton radiography, respectively. A 205 T strong magnetic field at the center of the coil target is generated in the free space at Iλ 2 of 6.85 × 10 14  W cm −2   μ m 2 , where I is the laser intensity, and λ is the laser wavelength. The magnetic field strength is proportional to Iλ 2 . Compared with the capacitor-coil target, the generation mechanism of the magnetic field is straightforward and the coil is easy to be fabricated.

Description: Abstract Electron scale magnetic cavities are electron vortex structures formed in turbulent plasma, while the evolution and electron dynamics of these structures have not been fully understood. Recently, high‐energy, angular, and temporal electron measurements from Magnetospheric Multiscale have enabled the application of an energetic particle sounding technique to these structures. This study analyzes an electron scale magnetic cavity observed by Magnetospheric Multiscale on 7 May 2015 in the plasma sheet. A comprehensive sounding technique is applied to obtain the geometry and propagation velocities of the boundaries. The result shows that the scale size of the structure is ∼90 km, and the leading and trailing boundaries are moving in the same direction but with different speeds (∼11.5 ± 2.2 and ∼18.1 ± 3.4 km/s, respectively). The speed difference suggests a shrinking of the structure that may play a significant role in magnetic energy dissipation and electron energization of electron scale magnetic cavities.

Description: The Dongsheng uranium deposit, the largest in-situ leach uranium mine in the Ordos Basin, geometrically forms a roll-front type deposit that is hosted in the Middle Jurassic Zhiluo Formation. The genesis of the mineralization, however, has long been a topic of great debate. Regional faults, epigenetic alterations in surface outcrops, natural oil seeps and experimental findings support a reducing microenvironment during ore genesis. The bulk of the mineralization is coffinite. Based on thin-section petrography, some of the coffinite is intimately intergrown with authigenic pyrite (ore-stage pyrite), and is commonly juxtaposed with some late diagenetic sparry calcite (ore-stage calcite) in primary pores, suggesting simultaneous precipitation. Measured homogenization temperatures of greater than 100 °C from fluid inclusions indicate circulation of low–temperature hydrothermal fluids in the ore zone. The carbon isotopic compositions of late calcite cement (δ 13 C VPDB = -31.0 to -1.4‰) suggest that they were partly derived from sedimentary organic carbon, possibly from deep-seated petroleum fluids emanating from nearby faults. Hydrogen and oxygen isotope data from kaolinite cement (δD = -133 to -116‰ and δ 18 O SMOW = 12.6 to 13.8‰) indicate that the mineralizing fluids differed from magmatic and metamorphic fluids, and were more depleted in D ( 2 H) than modern regional meteoric waters. Such a strongly negative hydrogen isotopic signature suggests that there has been selective modification of δD by CH 4 ±H 2 S±H 2 fluids. Ore-stage pyrite lies within a very wide range of δ 34 S (-39.2 to 26.9‰), suggesting that the pyrite has a complex origin, and that bacterially mediated sulfate reduction cannot be precluded. Hydrocarbon migration and its role in uranium reduction and precipitation have here been unequivocally defined. Thus, a unifying model for uranium mineralization can be established: early coupled bacterial uranium mineralization and hydrocarbon oxidation were followed by later recrystallization of ore phases in association with low-temperature hydrothermal solutions under hydrocarbon-induced reducing conditions. This article is protected by copyright. All rights reserved.

Description: The Mesoporous NiO nanosheets with an average thickness of ∼30 nm have been synthesized by annealing Ni(OH) 2 precursors. Magnetic measurements show that the NiO nanosheets can be considered as a core-shell type magnetic structure, in which the surface shell layer behaves as a coexistence of two-dimensional diluted antiferromagnetic (2D DAFF) and spin glass (SG) behaviors; the core retains its original bulk antiferromagnetic (AFM) phase. Field-cooled hysteresis loop measurements confirm the presence of exchange bias (EB) effect in the NiO nanosheets. The temperature dependence of the exchange bias field indicates that the observed EB effect originates from an interface exchange coupling interaction between the AFM core and the 2D DAFF shell layer. A phenomenological AFM-DAFF-SG magnetic structure model is proposed to interpret the magnetic properties of these NiO nanosheets.