一种耦合外部电路的脉冲感应推力器磁流体力学数值仿真模型

为了深入研究脉冲感应推力器的工作原理,预测其推进性能,建立了一种耦合外部电路的磁流体力学模型,实现了对加速通道内等离子体二维流场结构演化过程及驱动电路放电过程的同步耦合求解.模拟计算所得美国MK-1推力器加速通道内的等离子体瞬态参数分布及推力器比冲、效率等性能参数均与实验数据一致;计算结果成功复现了推力器的工作物理图景.借助这一新模型,实现了对电路-等离子体双向耦合作用的定量分析,分析结果表明:耦合等离子体导致驱动电路等效电阻增大,电感减小;激励线圈与等离子体之间的互感随等离子体整体远离线圈表面而逐渐减小.     

Superconductivity and Fermi Surface Anisotropy in Transition Metal Dichalcogenide NbTe_2

Transition metal dichalcogenides, featuring layered structures, have aroused enormous interest as a platform for novel physical phenomena and a wide range of potential applications. Among them, special interest has been placed upon WTe_2 and MoTe_2, which exhibit non-trivial topology both in single layer and bulk as well as pressure induced or enhanced superconductivity. We study another distorted IT material NbTe_2 through systematic electrical transport measurements. Intrinsic superconductivity with onset transition temperature(T_c~(onset)) up to 0.72 K is detected where the upper critical field(H_c) shows unconventional quasi-linear behavior,indicating spin-orbit coupling induced p-wave paring. Furthermore, a general model is proposed to fit the angledependent magnetoresistance, which reveals the Fermi surface anisotropy of NbTe_2. Finally, non-saturating linear magnetoresistance up to 50 T is observed and attributed to the quantum limit transport.     

基于多纵模拍频测量光纤色散

利用激光多纵模拍频频率与谐振腔色散系数的关系实现光纤的色散测量.测量系统采用可调光纤Fabry-Perot滤波器与光环行器构成窄带波长可调反射镜,作为光纤激光器的后腔镜,以光纤Sagnac干涉器作为前腔镜.将待测光纤置于谐振腔内,用频谱分析仪测量激光器拍频频率随激光输出波长的变化,得到待测光纤的色散系数.用该系统分别测量了色散补偿光纤和标准单模光纤的色散系数,实验结果表明该方法能够满足通信光纤的色散测量要求.该系统测量速度快、成本低、结构简单,具有良好的应用前景.     

基于分光光度计的食用油折射率实验研究

为获取不同食用油的光学色散特异性,须研究其折射率随波长变化特征.忽略光的散射影响后,建立了一种用于分光光度计的新双层载玻片模型,用此载玻片分别盛载菜籽油、芝麻油、餐厨废弃油、掺伪菜籽油、掺伪芝麻油,实验获取380~1500 nm的透射光谱,进而研究了5种油品的折射率随波长变化特征.研究结果表明5种油品的折射率随波长的变化特性较相似,在1210 nm、1400 nm波长处均出现折射率特征峰;各油品在其特征峰处的折射率有着显著的区别,5种油品在1210 nm波长处的折射率分别为1.512、1.472、1.456、1.576、1.612.此研究证实了新双层载玻片模型是可行的,共同折射率特征值与共同特征光谱标志着不同油品存在诸多关联性成分,5种油品在1210 nm波长处的折射率特征值,可以作为油品鉴别的有效指标.     

激光烧蚀聚甲醛的热-化学耦合模型及其验证

针对激光辐照聚甲醛的烧蚀现象,建立了一种包含升温、相变、热解及热解产物飞散等过程的热-化学耦合模型.采用无规热解模型描述聚甲醛升温后的热解过程,给出了不同热解率下热解产物的组成.利用基团贡献法计算烧蚀产物组分的热力学性质,并按照混合法则确定烧蚀产物混合物的名义标准沸点和临界温度.当烧蚀产物温度低于临界温度时,以液态蒸发机理表征热解产物的烧蚀,用Knudsen层关系式计算烧蚀质量;反之热解产物飞散由气体动力学机理控制,采用间断守恒关系及Jouguet条件描述烧蚀进程.本模型可给出激光辐照下聚甲醛的烧蚀质量、烧蚀温度、烧蚀产物组成和不同机理的烧蚀比率.与实验结果对比表明,当激光能量密度小于30 J/cm2时本模型能准确地描述烧蚀过程.     

Phase equilibrium of Cd_(1-x)Zn_xS alloys studied by first-principles calculations and Monte Carlo simulations

The first-principles calculations based on density functional theory combined with cluster expansion techniques and Monte Carlo(MC) simulations were used to study the phase diagrams of both wurtzite(WZ) and zinc-blende(ZB)Cd_(1-x)Zn_xS alloys.All formation energies are positive for WZ and ZB Cd_(1-x)Zn_xS alloys,which means that the Cd_(1-x)Zn_xS alloys are unstable and have a tendency to phase separation.For WZ and ZB Cd_(1-x)Zn_xS alloys,the consolute temperatures are 655 K and 604 K,respectively,and they both have an asymmetric miscibility gap.We obtained the spatial distributions of Cd and Zn atoms in WZ and ZB Cd_(0.5)Zn_(0.5)S alloys at different temperatures by MC simulations.We found that both WZ and ZB phases of Cd_(0.5)Zn_(0.5)S alloy exhibit phase segregation of Cd and Zn atoms at low temperature,which is consistent with the phase diagrams.     

基于激光拍频实现啁啾光纤光栅色散的测量

以啁啾光纤光栅为例,研究了激光拍频的产生机制,并建立对啁啾光纤光栅色散的测量模型.详细阐述了系统结构和测量原理,并对测量结果和理论值进行了分析与比较,结果一致性较好.在频谱分析仪分辨率为2.5kHz的情况下,色散测量准确度可以达到0.1ps,啁啾光纤光栅色散的实际测量也证实了该系统的可行性,系统相对简单,测量准确度高,可为色散测量提供参考.     

磁场对螺旋波等离子体波和能量吸收影响的数值研究

本文考察在径向电子数密度呈抛物形分布的情况下,外加稳恒磁场,射频通过螺旋波天线在等离子体中激发电磁波的传播性质.采用线性扰动波假设,数值求解Maxwell方程组,得到80—800 G(1 G=10-4T)磁场条件下等离子体中径向电、磁场强度及能量沉积密度的分布情形.计算结果表明,磁场增大(80→800G)时,螺旋波受到的阻尼较小,可深入等离子体传播;Trivelpiece-Gould(TG)波受到的阻尼增大,在等离子体-真空边界处衰减增强;整体的能量吸收向边界集中.磁感应强度小于100 G时,TG波可深入主等离子体区传播,等离子体径向能量吸收相对均匀.     

A radial non-uniform helicon equilibrium discharge model

Helicon discharges have attracted great attention in the electric propulsion community in recent years. To acquire the equilibrium properties, a self-consistent model is developed, which combines the helicon/Trivelpiece-Gould （TG） waves- plasma interaction mechanism and the plasma flow theory under the confinement of the magnetic field. The calculations reproduce the central peak density phenomenon observed in the experiments. The results show that when operating in the wave coupling mode, high magnetic field strength B0 results in the deviation of the central density versus B0 from the linear relationship, while the density rise becomes flatter as the radiofrequency （rf） input power Prf grows, and the electron temperature Te radial profile is mainly determined by the characteristic of the rf energy deposition. The model could provide suggestions in choosing the B0 and Prf for medium power helicon thrusters.