用电光采样法测量相对论电子束团长度

介绍了电光采样法测量电子束束团长度的实验原理和装置,理论分析并模拟计算了被测电子束团库仑场分布、ZnTe晶体的电光效应与束团电场的关系,并利用琼斯矩阵法分析了探测光通过电光晶体时在束团电场作用下的偏振变化、测量信号与束团长度的关系等。分析表明:测量中应使束团库仑场垂直于ZnTe的［001］方向,探测光偏振方向与ZnTe晶体y″轴成45°或者135°夹角,1/4波片快轴与探测光偏振方向夹角应取45°,这时平衡探测器输出信号与束团库仑场Eb成正比。1/4波片的作用是将电光晶体的工作点从非线性段移到线性段,平衡探测的作用是简化信号与Eb的关系,并提高信噪比。为实际测量应用提供参考。     

微波耦合场测量圆环探头的接收特性

 为了准确测量腔体等封闭狭小空间内微弱耦合电磁场,对一般小型圆环同轴探头的连接端面进行斜面剖分优化处理。采用时域有限差分方法,模拟了在电磁脉冲平面波激励下,圆环斜面探头所感应电压的时域变化过程。通过数值模拟计算,对比分析了３种不同角度斜面圆环探头的电磁接收频率响应特性,得出带有15°斜面圆环探头的高频接收性能相应提高2~5 dB。开展直径40 mm圆环15°斜面探头的电磁接收测量实验,并与相应计算结果进行对比分析,其二者整体变化趋势基本吻合,从而验证了数值计算分析探头电磁接收特性结果的准确性。     

Bi2223/Ag高温超导带材在脉冲电流下电磁特性分析

对高温超导带材在脉冲电流下的电磁特性进行了实验与仿真研究。实验部分对不同频率过电流下的伏安特性进行了测量,仿真部分运用有限元方法分析了电流和磁场分布特点。结果表明:在超导丝中,电流会因为频率的升高而呈现集肤效应,频率越高电流越向带材边缘集中,但与常规导体所不同的是,由于超导体各向异性的特点,边缘的非平行自场使该区域临界电流下降,导致电流密度最大的地方不是在带材的边缘,而是趋向于分布在磁场较弱的带材中部。     

Dielectric loss and electromagnetic absorption performance study of 1T/2H-MoS2/Mo2S3 nanocomposites with different ratios

High dielectric loss materials have an important application in electromagnetic (EM) absorption fields. In this paper, the ternary nanocomposites: 1T/2H-MoS₂/Mo₂S₃ with heterogeneous interfaces are synthesized by hydrothermal method. XRD, XPS, FTIR, SEM, and TEM measurements are applied to study the structure, morphology, and composition. The frequency spectra of complex permittivity (ε_r-f) are measured in 2–18 GHz by vector network analyzer. The results show that the nanocomposites have higher dielectric loss angle tangents than the reported 2H-MoS₂ absorbers. Based on the ε_r-f spectra, the reflection loss-frequency curves ($RL-f$) are simulated at given thicknesses. An effective absorption bandwidth of 5.2 GHz (12.8–18 GHz) and a $RL$ peak of −29.49 dB are achieved in a thin thickness of 1.62 mm, which are comparable to the reported 2H-MoS₂ absorbers with complex composition, showing that the 1T/2H-MoS₂/Mo₂S₃ nanocomposites have great application potential as an EM wave absorber in the K_u band.     

Towards efficient electromagnetic interference shielding performance for polyethylene composites by structuring segregated carbon black/graphite networks

An electromagnetic interference (EMI) shielding composite based on ultrahigh molecular weight polyethylene (UHMWPE) loaded with economical graphite-carbon black (CB) hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% (15 wt%) yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers (e.g., carbon nanotubes and graphene nanosheets) based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB (1/3, W/W) hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in turn provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.     

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介绍了EAST装置上的384道(极向24道径向16道)的外差混频式电子回旋辐射成像诊断系统及其在EAST及其复杂的电磁环境中的运行情况。在低杂波电流驱动期间,高灵敏度的电子回旋辐射成像系统受到严重干扰以至于无法提供正确的实验数据。通过优化系统各模块的接地、外加多层铜网屏蔽等措施,使得ECEI系统屏蔽效能与改善之前相比提高了40dB,基本保障了EAST装置上电子回旋辐射成像诊断的正常工作。     

Nonlinear Dynamics of Circularly Polarized Laser Pulse Propagating in a Magnetized Plasma with q ‐Nonextensive Velocity Distributions

The nonlinear dynamics of a circularly polarized laser pulse propagating in magnetized plasma contains hot nonextensive q ‐distributed electrons and ions is studied theoretically. A nonlinear equation which describes the dynamics of the slowly varying amplitude electromagnetic wave is obtained using the relativistic two‐fluids model. Some nonlinear phenomena include modulational instability, self‐focusing, soliton formation, and longitudinal and transversal evolutions of laser pulse in nonextensive plasma medium are investigated. Results show that the nonextensivity of particles can substantially change the nonlinearity of medium. The external magnetic field enhances the modulation instability growth rate of right‐hand polarization wave but for the left‐hand polarization the growth rate decreases. The spot size of the laser pulse is strongly affected by the plasma nonextensivity. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

PEDOT-PSS/Co-Fe_3O_4/PVA电磁功能复合纤维结构与性能

将化学共沉淀法合成的Co掺杂的Fe_3O_4(Co-Fe_3O_4)磁性粒子和化学氧化法合成的聚苯乙烯磺酸钠(PSS)掺杂的聚(3,4-乙撑二氧噻吩)(PEDOT-PSS)与聚乙烯醇(PVA)混合制备复合纺丝原液,然后经过湿法纺丝得到具有电、磁性能的PEDOT-PSS/Co-Fe_3O_4/PVA复合纤维.通过SEM、FTIR、XRD、TG、VSM以及电导率和机械性能的测试研究了不同牵伸倍率对复合纤维的结构和性能的影响.结果表明,随着牵伸倍率的增加,复合纤维的结晶性能、热稳定性能和机械性能都有所提升,其电导率则成倍增加,而其饱和磁化强度(M_s)则变化不大,约为1.7 A·m~2/kg.当牵伸倍数为4倍时,复合纤维的电导率可达到2.3 S/cm.     

Coulomb excitation of 74Ge beam

⁷⁴Ge beam was Coulomb-excited on a ^natPb target. Ten E2 matrix elements including diagonal matrix elements for 5 low-lying states have been determined using the least-squares search code GOSIA. The expectation values of the rotational invariants 〈Q ²〉 and 〈cos3δ〉 show the small and triaxial deformation of the two lowest members of the ground-state band , while the 0₂ ⁺ and 2₂ ⁺ states are found to be almost spherical. Received: 31 August 2000 / Accepted: 4 December 2000     

低空核爆炸在源区产生的电磁脉冲的近似估计

本文推导了在低空核爆炸的条件下,瞬发γ光子在源区中产生的电流和电场的近似解析公式,从这些解析公式给出的计算结果可看出,电场的前沿、陡度、峰值数值和半宽度的大小主要取决于弹体释放的瞬发γ光子的强度和时间特性。