分类： 核科学技术 >> 辐射物理与技术 提交时间： 2024-04-29
摘要： The layout and characteristics of the hard X-ray spectroscopy beamline (BL11B) at the Shanghai Synchrotron Radiation Facility are described herein. BL11B is a bending-magnet beamline dedicated to conventional millisecond-scale quick-scanning X-ray absorption fine structures. It is equipped with a cylindrical collimating mirror, a double-crystal monochromator comprising Si(111) and Si(311), a channel-cut quick-scanning Si(111) monochromator, a toroidal focusing mirror, and a high harmonics rejection mirror. It can provide 5–30 keV of X-rays with a photon flux of ~5 × 1011 photons/s and an energy resolution of ~ 1.31 × 10-4 at 10 keV. The performance of the beamline can satisfy the demands of users in the fields of catalysis, materials, and environmental science. This paper presents an overview of the beamline design and a detailed description of its performance and capabilities.
分类： 物理学 >> 核物理学 提交时间： 2024-03-08
Yu Xu
Yunsong Ning
Zhizhen Qin
Yao Teng
Changqing Feng
Jian Tang
Yu Chen
Yoshinori Fukao
Satoshi Mihara
Kou Oishi
摘要： COMET is a leading experiment to search for coherent conversion of $ mu^- mathrm{N} to e^- mathrm{N}$ with a high-intensity pulsed muon beamline, produced by the innovative slow extraction techniques. Therefore, it is critical to measure the characteristics of the muon beam. We set up a Muon Beam Monitor (MBM), where scintillation fibers (SciFi) weaved in the cross shape are coupled to silicon photomultipliers (SiPM), to measure the spatial profile and timing structure of the extracted muon beam for COMET. The MBM detector has been tested successfully with a proton beamline in China Spallation Neutron Source (CSNS) and taken data with good performance in the commissioning run called COMET Phase-$ alpha$. Experience of the MBM development, such as the mechanical structure and electronics readout, and its beam measurement results will be shared.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jia Huang
J. C. Kasper
L. A. Fisk
Davin E. Larson
Michael D. McManus
C. H. K. Chen
Mihailo M. Martinović
K. G. Klein
Luke Thomas
Mingzhe Liu
Bennett A. Maruca
Lingling Zhao
Yu Chen
Qiang Hu
Lan K. Jian
J. L. Verniero
Marco Velli
Roberto Livi
P. Whittlesey
Ali Rahmati
摘要： Switchbacks are rapid magnetic field reversals that last from seconds to hours. Current Parker Solar Probe (PSP) observations pose many open questions in regards to the nature of switchbacks. For example, are they stable as they propagate through the inner heliosphere, and how are they formed? In this work, we aim to investigate the structure and origin of switchbacks. In order to study the stability of switchbacks, we suppose the small scale current sheets therein may work to braid and stabilize the switchbacks. Thus, we use the partial variance of increments method to identify the small scale current sheets, and then compare their distributions in switchbacks. With more than one thousand switchbacks identified with PSP observations in seven encounters, we find many more current sheets inside than outside switchbacks, indicating that these micro-structures should work to stabilize the S-shape structures of switchbacks. Additionally, with the helium measurements, we study the variations of helium abundance ratios and alpha-proton differential speeds to trace switchbacks to their origins. We find both helium-rich and helium-poor populations in switchbacks, implying the switchbacks could originate from both closed and open magnetic field regions in the Sun. Moreover, we observe that the alpha-proton differential speeds also show complex variations as compared to the local Alfv\'en speed. The joint distributions of both parameters show that low helium abundance together with low differential speed is the dominant state in switchbacks. The presence of small scale current sheets in switchbacks along with the helium features are in line with the hypothesis that switchbacks could originate from the Sun via interchange reconnection process. However, other formation mechanisms are not excluded.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We report small-scale magnetic flux ropes via the Parker Solar Probe in situ measurements during the first six encounters and present additional analyses to supplement our prior work in Chen et al. 2021. These flux ropes are detected by the Grad-Shafranov-based algorithm with the duration and scale size ranging from 10 seconds to $\lesssim$1 hour and from a few hundred kilometers to 10$^{-3}$ au, respectively. They include both static structures and those with significant field-aligned plasma flows. Most structures tend to possess large cross helicity, while the residual energy distributes in wide ranges. We find that these dynamic flux ropes mostly propagate anti-sunward, with no preferential sign of magnetic helicity. The magnetic flux function follows a power law and is proportional to scale size. We also present case studies showing reconstructed two-dimensional (2D) configurations, which confirm that the static and dynamic flux ropes have the common configuration of spiral magnetic field lines (also streamlines). Moreover, the existence of such events hints at the interchange reconnection as a possible mechanism to generate flux rope-like structures near the Sun. Lastly, we summarize the major findings and discuss the possible correlation between these flux rope-like structures and turbulence due to the process of local Alfvenic alignment.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Increasingly one interplanetary coronal mass ejection (ICME) structure can propagate across more than one spacecraft in the solar wind. This usually happens when two or more spacecraft are nearly radially aligned with a relatively small longitudinal separation angle from one another. This provides multi-point measurements of the same structure and enables better characterization and validation of modeling results of the structures embedded in these ICMEs. We report such an event during October 13-14, 2019 when the Solar TErrestrial RElations Observatory Ahead (STA) spacecraft and the Parker Solar Probe (PSP) crossed one ICME structure at two different locations with nominal separations in both heliocentric distances and the longitudinal angles. We first perform an optimal fitting to the STA in-situ measurements, based on an analytic quasi-three dimensional (3D) model, yielding a minimum reduced $\chi^2=0.468$. Then we further apply the optimization approach by combining the magnetic field measurements from both spacecraft along their separate paths across the ICME structure. We find that the output based on the optimization (with the minimum reduced $\chi^2=3.15$) of the combined two-spacecraft dataset yields a more consistent result, given the much improved agreement of the model output with PSP data. The result demonstrates a magnetic flux rope configuration with clear 3D spatial variations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Magnetic flux rope, formed by the helical magnetic field lines, can sometimes remain its shape while carrying significant plasma flow that is aligned with the local magnetic field. We report the existence of such structures and static flux ropes by applying the Grad-Shafranov-based algorithm to the Parker Solar Probe (PSP) in-situ measurements in the first five encounters. These structures are detected at heliocentric distances, ranging from 0.13 to 0.66 au, in a total of 4-month time period. We find that flux ropes with field-aligned flows, although occur more frequently, have certain properties similar to those of static flux ropes, such as the decaying relations of the magnetic fields within structures with respect to heliocentric distances. Moreover, these events are more likely with magnetic pressure dominating over the thermal pressure. About one-third of events are detected in the relatively fast-speed solar wind. Taking into account the high Alfvenicity, we also compare with switchback spikes identified during three encounters and interpret their inter-relations. We find that some switchbacks can be detected when the spacecraft traverses flux rope-like structures. The cross-section maps for selected events are presented via the new Grad-Shafranov type reconstruction. Finally, the possible evolution of the magnetic flux rope structures in the inner heliosphere is discussed.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
JUNO Collaboration
Jie Zhao
Baobiao Yue
Haoqi Lu
Yufeng Li
Jiajie Ling
Zeyuan Yu
Angel Abusleme
Thomas Adam
Shakeel Ahmad
Rizwan Ahmed
Sebastiano Aiello
Muhammad Akram
Abid Aleem
Tsagkarakis Alexandros
Fengpeng An
Qi An
Giuseppe Andronico
Nikolay Anfimov
Vito Antonelli
摘要： The physics potential of detecting $^8$B solar neutrinos is exploited at the Jiangmen Underground Neutrino Observatory (JUNO), in a model independent manner by using three distinct channels of the charged-current (CC), neutral-current (NC) and elastic scattering (ES) interactions. Due to the largest-ever mass of $^{13}$C nuclei in the liquid-scintillator detectors and the potential low background level, $^8$B solar neutrinos would be observable in the CC and NC interactions on $^{13}$C for the first time. By virtue of optimized event selections and muon veto strategies, backgrounds from the accidental coincidence, muon-induced isotopes, and external backgrounds can be greatly suppressed. Excellent signal-to-background ratios can be achieved in the CC, NC and ES channels to guarantee the $^8$B solar neutrino observation. From the sensitivity studies performed in this work, we show that one can reach the precision levels of 5%, 8% and 20% for the $^8$B neutrino flux, $\sin^2\theta_{12}$, and $\Delta m^2_{21}$, respectively, using ten years of JUNO data. It would be unique and helpful to probe the details of both solar physics and neutrino physics. In addition, when combined with SNO, the world-best precision of 3% is expected for the $^8$B neutrino flux measurement.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Photonic spin Hall effect is a manifestation of spin-orbit interaction of light and can be measured by a transverse shift \lambda of photons with opposite spins. The precise measurement of transverse shifts can enable many spin-related applications, such as precise metrology and optical sensing. However, this transverse shift is generally small (i.e. \delta /\lambda {10}^{2}) have severe limitations, particularly its occurrence only over a narrow angular cone (with a width of \Delta \theta {70}^{\circ} by exploiting the interface between free space and uniaxial epsilon-near-zero media. The underlying mechanism is ascribed to the almost-perfect polarization splitting between s and p polarized waves at the designed interface. Remarkably, this almost-perfect polarization splitting does not resort to the interference effect and is insensitive to the incident angle, which then gives rise to the wide-angle giant photonic spin Hall effect.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Ziyang Yuan
Hongxia Wang
Zhiwei Li
Tao Wang
Hui Wang
Xinchao Huang
Tianjun Li
Ziru Ma
Linfan Zhu
Wei Xu
Yujun Zhang
Yu Chen
Ryo Masuda
Yoshitaka Yoda
Jianmin Yuan
Adriana Pálffy
Xiangjin Kong
摘要： Light-matter interaction is exploited in spectroscopic techniques to access information about molecular, atomic or nuclear constituents of the sample of interest. While scattered light carries both amplitude and phase information of the electromagnetic field, most of the time the latter is lost in intensity measurements. However, often the phase information is paramount to reconstruct the desired information of the target, as it is well known from coherent x-ray imaging. Here we introduce a new phase retrieval algorithm which allows us to reconstruct the field phase information from two-dimensional time- and energy-resolved spectra. We apply this method to the particular case of x-ray scattering off M\"ossbauer nuclei at a synchrotron radiation source. Knowledge of the phase allows also for an excellent reconstruction of the energy spectra from experimental data, which could not be achieved with this resolution otherwise. Our approach provides an efficient novel data analysis tool which will benefit x-ray quantum optics and M\"ossbauer spectroscopy with synchrotron radiation alike.
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