分类: 物理学 >> 核物理学 提交时间: 2024-03-10
摘要: Currently, three types of superconducting magnets are used in particle accelerators: cos2uptheta, CCT, and serpentine. However, all three coil configurations have complex spatial geometries, which make magnet manufacturing and strain-sensitive superconductor applications difficult. Compared with the three existing quadrupole coils, the racetrack quadrupole coil has a simple shape and manufacturing process, but there have been few theoretical studies. In this paper, the two-dimensional and three-dimensional analytical expressions for the magnetic field in coil-dominated racetrack superconducting quadrupole magnets are presented. The analytical expressions of the field harmonics and gradient are fully resolved and depend only on the geometric parameters of the coil and current density. Then, a genetic algorithm is applied to obtain a solution for the coil geometry parameters with field harmonics on the order of 10-4. Finally, considering the practical engineering needs of the accelerator interaction region, electromagnetic design examples of racetrack quadrupole magnets with high gradients, large apertures, and small apertures are described, and the application prospects of racetrack quadrupole coils are analyzed.
分类: 物理学 >> 核物理学 提交时间: 2023-12-15
摘要: Nondestructive and noninvasive neutron assays are essential applications of neutron techniques. Neutron resonance transmission analysis (NRTA) is a powerful nondestructive method for investigating the elemental composition of an object. The back-streaming neutron line (Back-n) is a newly built time-of-flight facility at the China Spallation Neutron Source (CSNS) that provides neutrons in the eV to 300 MeV range. A feasibility study of the NRTA method for nuclide identification was conducted at the CSNS Back-n via two test experiments. The results demonstrate that it is feasible to identify different elements and isotopes in samples using the NRTA method at Back-n. This study reveals its potential future applications.
分类: 光学 >> 显微镜 提交时间: 2023-11-15
摘要: Afull-field transmissionhardX-ray microscope (TXM) with 30nm resolution was designed and its prototype was constructed. The TXM relies on a compact, high stiffness, low heat dissipation and low vibration design philosophy and utilizes Fresnel Zone plate (FZP) as imaging optics. The design of the TXMwas introduced in detail, including the optical layout, the parameters of the FZP, the mechanical design of the TXM instrument. Preliminary imaging result with 52nm spatial resolution was achieved.
分类: 物理学 >> 核物理学 分类: 物理学 >> 地球物理学、天文学和天体物理学 提交时间: 2023-09-12
摘要: The neutron capture cross sections (${n, upgamma}$) of Bromine was performed with the time-of-flight (TOF) technique at the Back-n facility of the China Spallation Neutron Source (CSNS). Prompt $ upgamma$-rays originating from neutron-induced capture events were detected by four C${}_6$D${}_6$ detectors. The pulse height weighting technique (PHWT) and the double-bunch unfolding method based on the Bayesian theory were used in the data analysis. To obtain reliable measurement results, background deductions, normalization, and corrections were carefully considered. The multilevel R-matrix Bayesian code SAMMY was used to extract the resonance parameters in the resolved resonance region (RRR). The average cross sections in unresolved resonance region the was obtained from 10 to 400 keV. The experimental results were compared with the data of several evaluated libraries and previous experiments in the resolved and unresolved resonance region. The TALYS code was used to describe the average cross sections in the unresolved resonance region. Astrophysical Maxwell average cross sections (MACSs) of ${}^{79,81}$Br from $ kT $ = 5 to 100 keV was calculated over a sufficiently wide range of neutron energies. At a thermal energy of $kT=30$ keV, the MACS value for ${}^{79}$Br 638$ pm$64 mb is in good agreement with the KADoNiS recommended value. By contrast, the value of 293$ pm$29 mb for ${}^{81}$Br is substantially higher than those of the evaluated database and the KADoNiS recommended value.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2023-09-06
摘要: Theaim of this researchis to reconstruct the 3D X-ray refractive index gradient mapsbythe proposed vector Radon transform and its inverse, assuming that the small-angle deviation condition is met. Theoretical analysesshowthat the X-ray beam can be modeled as a streamline with continuous change of direction in a rowwhen measured in one grating period, which allowsthe extraction of the refraction angle signals.Experimental results show thatall the 2D refraction signals of different directions can be acquired by a standard circular scanning procedure, which is typically used in the X-ray differential phase-contrast computed tomography. Furthermore, the 3D refractive index gradient maps that contain the directional density changes, can also be accurately reconstructed.
分类: 物理学 >> 核物理学 提交时间: 2023-07-02
摘要: Significant evidence for a gravitational-wave background was reported by several pulsar-timing-array collaborations. By assuming that this signal is interpreted by the scalar-induced gravitational waves, we study physical implications of the observed signal for the nature of primordial curvature perturbations and primordial black holes. In particular, we explore the effects of primordial non-Gaussianity on the inferences of model parameters, and obtain the parameter region allowed by the observed signal, i.e., the primordial scalar spectral amplitude $A_S\sim10^{-2}-1$, the primordial non-Gaussian parameter $-10\lesssim f_{\mathrm{NL}} \lesssim 10$, and the mass of primordial black holes $m_{\mathrm{pbh}}\sim10^{-3}-0.1M_{\odot}$. We find that the non-Gaussianity suppressing the abundance of primordial black holes is preferred by the observed signal. We show that the anisotropies of scalar-induced gravitational waves are a powerful probe for measurements of the non-Gaussian parameter $f_{\mathrm{NL}}$, and conduct a complete analysis of the angular power spectrum in the nano-Hertz band. We expect that the Square Kilometre Array project has potentials to measure such anisotropies.
分类: 核科学技术 >> 核科学与技术 分类: 核科学技术 >> 粒子加速器 提交时间: 2023-06-20
摘要: With the development of high-performance photon sources which have extremely low emittance,autotuning magnet girders have drawn more and more attention, especially for diffraction-limited storagerings and free-electron lasers. The biggest challenge is to simultaneously obtain high stability and highflexibility. In this paper, an autotuning magnet-girder prototype has been designed and developed.Topological optimization, multipoint supports, and locking systems have been applied for magnet-girderdesign to improve the stability. The modal analysis accords with the vibration test well. The naturalfrequency of the magnet-girder assembly is deduced as high as 45.6 Hz, which demonstrates good stability.Ball-cam movers have been chosen as adjustment mechanisms, and a closed-loop control scheme has beenused to pursue high accuracy. The kinematic resolution is better than 1 m, and the accuracy is better than1 m within the adjusting range of #1;5 mm. Besides, it can eliminate most of the calibration, which cansave much manpower and time. The tests demonstrate that the magnet girder can be used for beam-basedgirder alignment with high stability and high accuracy.