聚变强磁场下真空测量电离规结构及阴极灯丝优化研究

基于强磁场环境中托卡马克装置偏滤器中性粒子压力快速测量,使用普通热阴极电离计,难以实现托卡马克偏滤器实验运行的原位精确测量.文章针对普通热阴极电离计的结构特点,首先探究了强磁场下,阴极发射电子的运动轨迹受磁场约束对规管灵敏度的影响.应用有限元方法,计算分析了阴极灯丝受电动力以及热应力和电动力耦合作用下发生形变的规律,得到阴极灯丝应力、总变形量和轴向变形量数据以及阴极灯丝的热力性能不受加热电流变化影响的结论.提出可在强磁场下稳定工作的规管结构设计方案,得到阴极灯丝优化结果,为聚变装置强磁场下真空测量快规的优化设计提供参考.     

A Study on Thermal Response of Nanoparticles in External Magnetic Field

Journal of Superconductivity and Novel Magnetism - Hyperthermia has become an important area of research for cancer treatment throughout the world. Choosing appropriate magnetic nanoparticles for...     

Fluctuation Hall Conductivity Beyond Linear Response in Layered Superconductors Under a Magnetic Field

We calculate fluctuation Hall conductivity of a strongly type-II superconductor in strong electric fields by using the time dependent Ginzburg–Landau approach. Thermal fluctuations, represented by the Langevin white noise, are assumed to be strong enough to melt the Abrikosov vortex lattice created by the magnetic field into a moving vortex liquid. The layered structure of the superconductor is accounted for by means of the Lawrence–Doniach model. The nonlinear interaction term in dynamics is treated within self-consistent Gaussian approximation and we go beyond the often used lowest Landau level approximation to treat arbitrary magnetic fields. The results are compared to experimental data on high-T _c superconductor YBa₂Cu₃O_7?δ .     

Magnetic Response of Ferromagnet-Superconductor-Ferromagnet (Gd/Nb/Gd) Trilayer

Magnetic measurements on Gd(30 nm)/Nb(70 nm)/Gd(30 nm) trilayer were performed with the field applied parallel to the plane of the film. Ferromagnetic transition was observed at temperature of about 285 K and the superconducting transition was suppressed to 6 K. A novel finding of the study is the observation of rearrangement of ferromagnetic domains in magnetic Gd layers induced by the traversal of the trilayer through the superconducting state in the adjoining Nb layer.     

Noise Characteristics of the Optical Response of Ferrofluids to a Magnetic Field

Technical Physics Letters - The noise generated by different ferrofluid samples when probed by the fiber-optic method has been investigated. It is shown that switching on a magnetic field...     

Magnetic Field Dependence of CDW Phases in (Per)2M(mnt)2 (M = Pt, Au)

Recently the authors discovered that the suppression of the charge density wave (CDW) ground states by high magnetic fields in the organic conductor series (Per)₂M(mnt)₂ is followed by additional high field, CDW-like phases. The purpose of this paper is to review these compounds and to consider the relevant parameters of the materials that describe the manner in which the CDW ground state may undergo new field induced changes above the Pauli limit.     

Magnetic susceptibility measurements in PrBe13

The temperature dependent complex magnetic susceptibility of the Van Vleck paramagnet PrBe ₁₃ has been measured at temperatures below 20 mK in zero magnetic field. We observe an antiferromagnetic Curie-Weiss behaviour of the nuclear spin susceptibility with a Weiss temperature = -2.2 mK.     

Quantum (Nano-Scale) Limit in a Parallel Magnetic Field in Layered Q1D Conductors

We show that electron wave functions in a quasi-one-dimensional (Q1D) layered conductor in a parallel magnetic field are always localized on conducting layers. Wave functions and electron spectrum in a quantum limit, where the “sizes” of quasi-classical electron orbits are of the order of nanoscale distances between the layers, are determined. Possible applications of our results to physical properties of Q1D materials in their superconducting and metallic phases are discussed.     

Simulation of Giant Magnetic Impedance (GMI) Effect in Co-based Amorphous Ribbons with Demagnetizing Field

Considering the role of demagnetizing field, based on linear Maxwell’s equations and the Landau-Lifshitz equation, the expressions of permeability and impedance were obtained using the improved theoretical model in this article. A numerical simulation was conducted using Matlab, and the results of calculations were well matched with the experimental results, indicating the importance of the demagnetizing field and that it should not be ignored. Utilizing the equivalence relation between the shape of the samples and the demagnetization factor which determined the value of the demagnetizing field, the influence of the aspect ratio of the samples on giant magnetic impedance (GMI) effect was researched. The calculations showed that the most significant GMI effect was obtained when the aspect ratio of samples was about 44. In addition, the optimal frequency to obtain the most significant GMI effect of the given sample was calculated. These researches may provide theoretical guidance for the development and use of a GMI sensor.     

Unconventional Field Dependence of Magnetoresistance of (TMTSF)2ClO4 Studied by 46-T Pulsed Magnetic Field System

A new TTP donor, Me-DH-TTP (2-methyl-5-(1,3-dithiolan-2-yliden)-1,3,4,6-tetrathiapentalene), was designed to realize a system with large on-site Coulomb repulsion as compared with the previously known bis-fused type TTP donors. Probably as a consequence, (Me-DH-TTP)₂AsF₆ exhibits semiconducting behavior from room temperature to liquid helium temperature. By increasing pressure, metallic behavior appears below 300 K, and with distinct metal-insulator (M-I) transition up to 2.2 GPa. This M-I transition suddenly disappears beyond 2.5 GPa, and metallic state is stabilized down to 2.6 K. We discuss the possibility of quantum critical point around 2.4 GPa.     

Soft Magnetic Properties of FeSiCr Cores in a Transverse Magnetic Field

Journal of Superconductivity and Novel Magnetism - In this paper, the magnetic properties of small-sized FeSiCr core under strong transverse magnetic field are studied. The test results show that a...     

Determining Magnetic Field Source Coordinates

The paper discusses determining the coordinates of a magnetic field source from measure predictions of the magnetic inductance vector obtained with four or five three-component magnetometric sensors.     

Layered Superconductors in an External Magnetic Field

Presence of localized magnetic moments and inhomogeneites leads to an unconventional behavior of the upper critical field for layered superconductors. In addition, one can observe a large diamagnetic moment at H H _c2 and in the normal resistive state.     

铝锡合金电磁搅拌中电磁场的模拟分析

Al-8Sn-2Si-2Pb-0.8Cu-0.2Cr铝合金是具有优越性能的复合轴瓦材料,但容易产生比重偏析,需要进行搅拌。通过对搅拌器的电磁场模拟计算,得到了最佳工艺参数,采用5组线圈,相位差为90°,频率为50Hz,电压为7V,计算结果与实验值很吻合,对科研具有指导作用。     

Comparison of Magnetic Field Analysis Methods Considering Magnetic Anisotropy

The magnetic field analysis results on grain-oriented silicon steel sheet and nongrain-oriented silicon steel sheet by the isotropic method, the two-axis isotropic method, the two-axis anisotropic method, the $varphi$ anisotropic method, and the $theta_{rm HB}$ anisotropic method, which are 2-D magnetic analysis methods, are compared. In analyzing the magnetic field in the isotropic material, the isotropic method is more appropriate than the two-axis isotropic method. For the anisotropic material in which the magnetic flux density is much less than saturation magnetic flux density, the two-axis anisotropic method is more preferable than the $varphi$ anisotropic method, because the result of the two-axis anisotropic method is similar to that of the $theta_{rm HB}$ anisotropic method. However, for the analysis in high magnetic flux density near the saturation magnetic flux density, the $varphi$ anisotropic method is more suitable than the two-axis anisotropic method.      

The Transport Properties of Li(1+x)Ti2O4 in High Magnetic Field

The spinel oxide superconductor LiTi₂O₄ shows intricate transport properties in both normal state and superconducting state. The Hall effect measurements exhibit an abrupt change in carrier density near T=170 K where the temperature derivative of resistivity changes sign from negative to positive on cooling. In addition, the sample shows significant positive magnetoresistance below 40 K, e.g., R(H)/R(H=0)3% at T=14 K and H=16 T. A most interesting feature is the magnetic field effect on the resistivity near the superconducting state. In addition to the field-induced broadening of R(T), there exhibits an anomalous upturn in R(T) near the superconducting regime when magnetic field is above 3T. The temperature T ₁ at which R(T) shows upturn linearly correlates with magnetic field H and can be expressed as T ₁/T _C(H=0)=1–0.04H for 3T<H<12T. The superconductivity is completely suppressed at field above 14T and the low temperature resistance behaves semiconductor-like.     

磁悬浮运动平台的磁场分析及优化设计

研制了一种新型磁悬浮平台,该平台定子采用无铁心式的克莱姆绕组,消除了固有齿槽效应,动子采用Halbach 磁阵列结构方式,由于平台输出推力与悬浮的稳定性主要与其气隙磁场的分布情况有直接关系,因此提高气隙磁场的正弦分布是改善其工作特性的难点和重点. 为了改善气隙磁场的分布问题,提出了一个优化磁场分布的目标函数,并采用步长加速法对平台磁场进行了优化设计,大大降低了磁场谐波分量,改善了气隙磁场分布状态. 将优化结果运用到实际的平台中,对该运动平台进行了阶跃响应实验,实验结果表明满足平台需要达到纳米级精度的要求.