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Polarization analysis for magnetic field imaging at RADEN in J-PARC/MLF
摘要： Polarized neutron imaging is an attractive method for visualizing magnetic fields in a bulk object or in free space. In this technique polarization of neutrons transmitted through a sample is analyzed position by position to produce an image of the polarization distribution. In particular, the combination of three-dimensional spin analysis and the use of a pulsed neutron beam is very effective for the quantitative evaluation of both field strength and direction by means of the analysis of the wavelength dependent polarization vector. Recently a new imaging instrument “RADEN” has been constructed at the beam line of BL22 of the Materials and Life Science Experimental Facility (MLF) at J-PARC, which is dedicated to energy-resolved neutron imaging experiments. We have designed a polarization analysis apparatus for magnetic field imaging at the RADEN instrument and have evaluated its performance.
关键词： polarization analysis,Polarized neutron imaging,RADEN,J-PARC/MLF,magnetic field imaging
更新于2025-09-23 15:19:57
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Combining Faraday Tomography and Wavelet Analysis
摘要： We present a concept for using long-wavelength broadband radio continuum observations of spiral galaxies to isolate magnetic structures that were only previously accessible from short-wavelength observations. The approach is based on combining the RM Synthesis technique with the 2D continuous wavelet transform. Wavelet analysis helps to isolate and recognize small-scale structures which are produced by Faraday dispersion. We ?nd that these structures can trace galactic magnetic arms as illustrated by the case of the galaxy NGC 6946 observed at λ = 17–22 cm. We support this interpretation through the analysis of a synthetic observation obtained using a realistic model of a galactic magnetic ?eld.
关键词： wavelet analysis,RM-synthesis,faraday depolarization,galactic magnetic field
更新于2025-09-19 17:15:36
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Apparent delocalization of the current density in metallic wires observed with diamond nitrogen-vacancy magnetometry
摘要： We report on a quantitative analysis of the magnetic field generated by a continuous current running in metallic microwires fabricated on an electrically insulating diamond substrate. A layer of nitrogen-vacancy (NV) centers engineered near the diamond surface is employed to obtain spatial maps of the vector magnetic field, by measuring Zeeman shifts through optically detected magnetic resonance spectroscopy. The in-plane magnetic field (i.e., parallel to the diamond surface) is found to be significantly weaker than predicted, while the out-of-plane field also exhibits an unexpected modulation. We show that the measured magnetic field is incompatible with Ampère’s circuital law or Gauss’s law for magnetism when we assume that the current is confined to the metal, independent of the details of the current density. This result was reproduced in several diamond samples, with a measured deviation from Ampère’s law by as much as 94(6)% (i.e., a 15σ violation). To resolve this apparent magnetic anomaly, we introduce a generalized description whereby the current is allowed to flow both above the NV sensing layer (including in the metallic wire) and below the NV layer (i.e., in the diamond). Inversion of the Biot-Savart law within this two-channel description leads to a unique solution for the two current densities that completely explains the data, is consistent with the laws of classical electrodynamics, and indicates a total NV-measured current that closely matches the electrically measured current. However, this description also leads to the surprising conclusion that in certain circumstances the majority of the current appears to flow in the diamond substrate rather than in the metallic wire, and to spread laterally in the diamond by several micrometers away from the wire. No electrical conduction was observed between nearby test wires, ruling out a conventional conductivity effect. Moreover, the apparent delocalization of the current into the diamond persists when an insulating layer is inserted between the metallic wire and the diamond or when the metallic wire is replaced by a graphene ribbon. The possibilities of a measurement error, a problem in the data analysis, or a current-induced magnetization effect are discussed, but do not seem to offer a more plausible explanation for the effect. Understanding and mitigating this apparent anomaly will be crucial for future applications of NV magnetometry to charge transport studies.
关键词： diamond magnetometry,nitrogen-vacancy centers,Biot-Savart law,Ampère's law,magnetic field imaging,current density
更新于2025-09-19 17:15:36
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Simultaneous measurement of magnetic field and temperature based on NCF cascaded with ECSF in fiber loop mirror
摘要： In this paper, we propose and experimentally demonstrate a dual-parameter sensor based on no-core fiber (NCF) cascaded with elliptical-core spun fiber (ECSF) in a Sagnac loop. Both NCF and ECSF are sealed in a capillary with the magnetic fluid to detect the magnetic field and temperature simultaneously. By introducing a section of NCF inside an elliptical-core spun fiber loop mirror (E-FLM) with optimizing fiber length, two extinct dips can be observed from 1480 to 1680 nm in the transmission spectrum. One dip is the result of multimode interference (MMI), while the other is induced by Sagnac interference of E-FLM. Hence, the simultaneous measurement of magnetic field and temperature can be realized by monitoring the shift of different wavelengths of two dips. Experimental results show that the dip of MMI is sensitive to the magnetic field (713.07 pm/mT), while the E-FLM has almost no response to magnetic field. For the two dips monitored in the temperature measurement, the sensitivities of proposed sensor are ?34.8 pm/°C and 304.55 pm/°C, respectively.
关键词： Multimode interference,Fiber loop mirror,Magnetic field measurement,Temperature measurement
更新于2025-09-19 17:15:36
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Study of laser-driven magnetic fields with a continuous wave Faraday rotation diagnostic
摘要： Magnetic ?elds driven by a laser in coil targets were studied for laser energies of (cid:2)25 J and two pulse durations of 2.8 ns and 70 ps. Axial magnetic ?elds in the coils were measured by continuous wave Faraday rotation diagnostics. The diagnostics indicated magnetic ?elds of 6–14 T in the coil and currents of 10–20 kA. Magnetic ?elds were compared for similar laser targets, focusing conditions, and laser energies. A 30-times increase in the intensity of the laser beam by reducing the pulse duration resulted in an increase in the magnetic ?eld and current by a factor of 2. The relaxation time of the magnetic pulse was on the sub-microsecond scale.
关键词： coil targets,magnetic field measurement,laser-driven magnetic fields,pulse duration,Faraday rotation diagnostics
更新于2025-09-19 17:13:59
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Radial Nanowire Assemblies under Rotating Magnetic Field Enabled Efficient Charge Separation
摘要： Developing efficient charge separation strategies is essential to achieve high power conversion efficiency in fields of chemistry, biology and material science. Herein, we develop a facile strategy for fabrication of unique wafer-scale radial nanowire assemblies by exploiting shear force in rotary solution. The assembling mechanism can be well revealed by the large-scale stochastic dynamics simulation. Free electrons can be rapidly generated to produce quantitatively tunable current output when the radial nanowire assemblies rotating under the magnetic field. Moreover, the photoconductive performance of the radial semiconductor nanowire assemblies can be remarkably enhanced as the electron-hole recombination was retrained by the efficient charge separation under the rotating magnetic field. Such large-scale unique nanowire assemblies will facilitate the design of efficient charge separation process in bio-system, sensors and photocatalysis.
关键词： nanowires,charge separation,stochastic dynamics simulation,assembly,magnetic field
更新于2025-09-19 17:13:59
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Recycling of silicon scraps by directional solidification coupled with alternating electromagnetic field and its electrical property
摘要： In this paper, alternating electromagnetic field and directional solidification are used to separate SiC and Si3N4 in polycrystalline silicon tailings. It is found the inclusion particles move downward at the center of the ingot and moving upward at the edge of the ingot by a variety of forces during the directional solidification process. The electromagnetic force accelerates the melt flow and enhances the lift force, so that larger particles can be pushed to the top of the ingot. Rod-shaped Si3N4 and block-shaped SiC particles show symbiotic relationship between each other. The aggregation of inclusion particles adsorbs metallic impurities, especially volatile metals, due to the effects of mushy region and short-circuit diffusion. The average conversion efficiency of the solar cells (Al-BSF method) prepared using the recycled silicon reached 18.56%, which meets the demand of the solar cells.
关键词： SiC,Alternating magnetic field,Directional solidification,Si3N4,Polycrystalline silicon
更新于2025-09-19 17:13:59
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Strong coupling of two quantum dots with a microcavity in the presence of an external and tilted magnetic field
摘要： Including an external magnetic field B in a Tavis-Cummings model enables us to consider four exciton states in each quantum dot, two brights and two darks. With a continuous and incoherent pump to a cavity, we explore the conditions of occupation and emission as a function of B. We have found that although the dark excitons are optically inactive, these show a trace of emission as a result of both the strong coupling between light and matter and the interaction between bright and dark exciton states mediated by the magnetic field. Further, tuning one of the quantum dots at resonance with the cavity, we report the set of parameters that allows us to change the resonance condition between exciton states from different quantum dots, namely, we use the magnetic field as a control parameter to select which exciton state and which quantum dot will be mostly coupled to the cavity.
关键词： strong coupling,magnetic field,quantum dots,exciton states,microcavity
更新于2025-09-19 17:13:59
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Enhanced relativistic-electron beam collimation using two consecutive laser pulses
摘要： The double laser pulse approach to relativistic electron beam (ReB) collimation in solid targets has been investigated at the LULI-ELFIE facility. In this scheme two collinear laser pulses are focused onto a solid target with a given intensity ratio and time delay to generate REBs. The magnetic field generated by the first laser-driven REB is used to guide the REB generated by a second delayed laser pulse. We show how electron beam collimation can be controlled by properly adjusting the ratio of focus size and the delay time between the two pulses. We found that the maximum of electron beam collimation is clearly dependent on the laser focal spot size ratio and related to the magnetic field dynamics. Cu-Kα and ctR imaging diagnostics were implemented to evaluate the collimation effects on the respectively low energy (≤100 keV) and high energy (≥MeV) components of the REB.
关键词： relativistic electron beam,magnetic field dynamics,laser pulses,CTR imaging,Cu-Kα imaging,collimation
更新于2025-09-19 17:13:59
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Circular quantum dots in twisted bilayer graphene
摘要： Within a tight-binding approach, we investigate the effect of twisting angle on the energy levels of circular bilayer graphene (BLG) quantum dots (QDs) in both the absence and presence of a perpendicular magnetic field. The QDs are defined by an infinite-mass potential, so that the specific edge effects are not present. In the absence of magnetic field (or when the magnetic length is larger than the moiré length), we show that the low-energy states in twisted BLG QDs are completely affected by the formation of moiré patterns, with a strong localization at AA-stacked regions. When magnetic field increases, the energy gap of an untwisted BLG QD closes with the edge states, localized at the boundaries between the AA- and AB-stacked spots in a twisted BLG QD. Our observation of the spatial localization of the electrons in twisted BLG QDs can be experimentally probed by low-bias scanning tunneling microscopy measurements.
关键词： moiré patterns,tight-binding model,twisted bilayer graphene,magnetic field,quantum dots
更新于2025-09-19 17:13:59