Two dynamics modes in planar wire array Z pinch implosion

Two dynamics modes,named short ablation mode and long ablation mode,are observed in implosion experiments of planar wire array Z pinch on ’QiangGuang-I’ facility utilizing an optical streak camera.The long ablation mode has a lagged trajectory compared with the short ablation mode.For shot 10035 in a short ablation mode,the initial time of K-shell radiation is consistent with the interaction time for ablation plasma arriving at the centre of wire array,while for shot 10038 in long ablation mode,the initial time of K-shell radiation is about 10 ns earlier.In the two modes,the partial ablation plasma could traverse the wire array plane and then collide in the centre to form a dense plasma column with a diameter of 2.2 mm for shot 10035 and 1.5 mm for shot 10038.     

A Novel Model of Interaural Time Difference Based on Spatial Fourier Analysis

Based on the spatial Fourier analysis, a statistical model of the individualized interaural time difference （ITD） is derived from the head-related transfer function database for a Chinese subject. The model reflects the spatial left-right symmetry and front-back asymmetry of lTD. Moreover, by using three anatomical parameters of head and pinna, the model is able to predict individualized ITD in the horizontal plane. Performance of the four subjects outside the database demonstrates that the mean of the total error is less than 20 μs, while the lateral performance is inferior to that at other directions.     

Velocity estimation of an airplane through a single satellite image

The motion information of a moving target can be recorded in a single image by a push-broom satellite.A push-broom satellite image is composed of many image lines sensed at different time instants.A method to estimate the velocity of a flying airplane from a single image based on the imagery model of the linear push-broom sensor is proposed.Some key points on the high-resolution image of the plane are chosen to determine the velocity（speed and direction）.The performance of the method is tested and verified by experiments using a WorldView-1 image.     

Tuning Out-of-Plane Spin Polarization Using in-Plane Magnetic Fields in a Quasi-One-Dimensional Quantum Wire Embedded in （110） Plane

We investigate theoretically the combination effect of an in-plane magnetic field and spin-orbit interactions （SOIs） on the spin and charge transport property of a quasi-one-dimensional quantum wire embedded in the （110） crystallographic plane. We find that the oscillations of the conductance induced by the SOIs become more significant and different for the spin-up and spin-down electrons in the presence of the in-plane magnetic field. The conductance exhibits a significant anisotropic behavior and electrons exhibit out-of-plane spin polarization which can be tuned by an in-plane magnetic field. These features offer us an efficient way to control SOI-induced spin transport using in-plane magnetic fields.     

Effect of Time Delay on Binary Signal Detection via a Bistable System

The effect of time delay on binary signal detection via a bistable system in the presence of white or colored Gaussian noise is investigated. By defining the bit error rate based on the solution of the approximated Fokker- Planck equation, the detector performance is investigated theoretically and is verified by Monte Carlo simulation. It is shown that, when the system parameter or noise intensity is optimally chosen, the increasing time delay generally improves the system performance. It is also shown that it is more difficult to accurately predict the system performance with a larger time delay and correlation time. This may inspire more thorough investigations in cooperative effects of a nonlinear system and time delay on signal processing.     

Hofstadter＇s Butterfly and Phase Transition of Checkerboard Superconducting Network in a Magnetic Field

We study the magnetic effect of the checkerboard superconducting wire network. Based on the de Gennes- Alexader theory, we obtain difference equations for superconducting order parameter in the wire network. Through solving these difference equations, we obtain the eigenvalues, linked to the coherence length, as a function of magnetic field. The diagram of eigenvalues shows a fractal structure, being so-called Hofstadter＇s butterfly. We also calculate and discuss the dependence of the transition temperature of the checkerboard superconducting wire network on the applied magnetic field, which is related to up-edge of the Hofstadter＇s butterfly spectrum.     

Design and optimization of resistive anode for a two-dimensional imaging GEM detector

A resistive anode for two-dimensional imaging detectors,which consists of a series of high resistivity pads surrounded by low resistivity strips,can provide good spatial resolution while reducing the number of electronics channels required.The optimization of this kind of anode has been studied by both numerical simulations and experimental tests.It is found that to obtain good detector performance,the resistance ratio of the pads to the strips should be larger than 5,the nonuniformity of the pad surface resistivity should be less than 20%,a smaller pad width leads to a smaller spatial resolution,and when the pad width is 6 mm,the spatial resolution(σ) can reach about 105μm.Based on the study results,a 2-D GEM detector prototype with optimized resistive anode is constructed and a good imaging performance is achieved.     

X-ray observations of tungsten wire array Z-pinch implosions on QiangGuang-1 facility

Z-pinch experiments with two arrays consisting, respectively, of 32 4-μm- and 6-μm-diameter tungsten wires have been carried out on QiangGuang-1 facility with a current rising up to 1.5MA in 80ns. At early time of implosion, x-ray framing images show that the initial emission comes from the central part of arrays, and double clear emission rings, drifting to the anode and the cathode at 5×10⁶cm/s and 2.4×10⁷cm/s respectively, are often produced near the electrodes. Later, in a 4-μm-diameter tungsten wire array, filamentation caused by ohmic heating is prominent, and more than ten filaments have been observed. A radial inward shift of arrays starts at about 30\,ns earlier than the occurrence of the x-ray peak power for both kinds of arrays, and the shrinkage rate of emission region is as high as 1.7×10⁷cm/s in a 4-μm-diameter tungsten wire array, which is two times higher than that in a 6-μm one. Emission from precursor plasmas is observed in implosion of 6-μm-diameter tungsten wire arrays, but not in implosion of a 4-μm-diameter tungsten wire array. Whereas, in a 4-μm-diameter tungsten wire array, the soft x-ray emission shows the growth of m=1 instability in the plasma column, which is caused by current. The reasons for the discrepancy between implosions of 4-μm- and 6-μm-diameter tungsten wire arrays are explained.     

Simplified triangular ground plane cloak by oblique multilayer dielectrics

Based on the effective medium theory, the triangular ground plane cloak can be realized by thin layered systems. Two solutions of parameter setting of the layered cloak are suggested to demonstrate the invisibility performance of a hybrid incoming wave. The hybrid parameters are derived from the equivalent of both anisotropies of permittivity and permeability to the alternating layers. The performance of the designed layered cloak is validated by both TM and TE wave simulations with near-field distributions and average scattering power outflows on an observation semicircle. From the simulation results, the layered cloak with both hybrid parameters and improved hybrid parameters can reflect the incoming TM/TE waves in a specular direction, and the latter behaves with a better overall invisibility performance.     

A Novel Nano-Grating Structure of Polarizing Beam Splitters

A metal wire nanograting is fabricated and used as a polarizing beam splitter that reflects TE polarization and transmits TM polarization. The metal wire nanograting is based on a fully optimized design structure that consists of not only the core nanowire metal grid but also the substrate nanograting. The substrate nanograting is designed to provide better performance for both TM and TE polarizations. We fabricate metal-stripe gratings on a glass substrate using nanoimprint lithography and reactive ion etching process. A detailed investigation of the polarization effect at 1550 nm wavelength is carried out with the theoretical analysis and experimental results. The polarizing beam splitter has uniform performance with wide variations in the incident angle （±25） and has high efficiency for both the reflected and the transmitted beams.     

Interdiffusion of Al-Ni system enhanced by ultrasonic vibration at ambient temperature

At ambient temperature, Al–1%Si wire of 25 μm diameter was bonded successfully onto the Au/Ni/Cu pad by ultrasonic wedge bonding technology. Physical process of the bond formation and the interface joining essence were investigated. It is found that the wire was softened by ultrasonic vibration, at the same time, pressure was loaded on the wire and plastic flow was generated in the bonding wire, which promoted the diffusion for Ni into Al. Ultrasonic vibration enhanced the interdiffusion that resulted from the inner defects such as dislocations, vacancies, voids and so on, which ascribed to short circuit diffusion.     

抛光垫磨损非均匀性研究

抛光垫是化学机械抛光的重要组成部分,其磨损的非均匀性对被加工工件面型精度和抛光垫修整有重要影响。基于直线摆动式抛光方式,研究了抛光过程中抛光垫与工件的相对运动,建立了抛光垫磨损模型,分析了抛光工艺参数对抛光垫磨损及均匀性的影响。研究结果表明,工件与抛光垫的转速比为1.11,正弦偏心直线摆动形式,摆动幅度系数为2,摆动频率系数在0.1~0.2之间,抛光垫表面磨损更均匀,并根据抛光垫表面磨损特性优化了抛光垫形状。优化的抛光垫具有更好的面型保持性,延长了修整间隔,为抛光工艺设计提供理论指导。     

Experimental studies of micromegas detectors with different micro-meshes

The structure of micromegas (micro-mesh gaseous structure) detectors with different micro-meshes of stainless steel wire woven netting and Ni foil has been presented. The counting rates, energy resolution, gain, discharge probability and time resolution have been measured. Wider counter plateaus and gain for the developed detector were obtained. Excellent energy resolution of the micromegas detector, 17% (FWHM) based on Ni foil micro-mesh and 25% (FWHM) based on stainless steel wire woven netting micro-mesh, has been obtained for the 5.9 keV photon peak of the ⁵⁵Fe X-ray source in an Ar/CO₂(10%) gas mixture. The best time resolution at -620 V micro-mesh voltage and -870 V drift voltage is 14.8 ns for cosmic rays in an Ar/CO₂(10%) gas mixture. These results satisfy the basic demand of the micromegas detector preliminary design.     

Novel pad structures for the improvement of wire bonding strength in DXD panel

New pad structures are suggested to improve the wire bonding strength in the TFT panels suitable for the flat panel X-ray detector application. Several candidates of bonding pad structure are tested and one of them is chosen which shows the strongest and the most stable bonding with aluminum wire. Some morphological consideration was adopted to the surface of AlNd (Nd 2 at.%) pads whose thickness are 4000 Å. To avoid the defect of signal lines such as hillocks due to increased thickness of AlNd, we selectively increased the thickness of AlNd on the bonding area only.     

Experimental studies of micromegas detectors with different micro-meshes

The structure of micromegas (micro-mesh gaseous structure) detectors with different micro-meshes of stainless steel wire woven netting and Ni foil has been presented. The counting rates, energy resolution, gain, discharge probability and time resolution have been measured. Wider counter plateaus and gain for the developed detector were obtained. Excellent energy resolution of the micromegas detector, 17% (FWHM) based on Ni foil micro-mesh and 25% (FWHM) based on stainless steel wire woven netting micro-mesh, has been obtained for the 5.9 keV photon peak of the 55Fe X-ray source in an Ar/CO2(10%) gas mixture. The best time resolution at -620 V micro-mesh voltage and -870 V drift voltage is 14.8 ns for cosmic rays in an Ar/CO2 (10%) gas mixture. These results satisfy the basic demand of the micromegas detector preliminary design.     

Studies on the drift properties and spatial resolution using a microMEGAS-equipped time projection chamber

R&D studies on the performance as well as on the gas properties of the microMEGAS-based time projection chamber with standard readout were carried out in June 2005 using 4 GeV/c pion beam in a magnetic field from 0 to 1 T at the proton synchrotron beam line at KEK, Japan. Analysis of the electron drift velocity, diffusion constant and point resolution of padrow measurement for MicroMEGAS TPC filled with 95% argon and 5% isobutane gas are presented. The underlying physical mechanism which determines the optimal TPC performance are briefly discussed. Preliminary measurements of gas properties and spatial resolution in close agreement with the analytical calculation and MAGBOLTZ simulation are summarized and presented in this paper.      

Development of a portable and fast wire tension measurement system for MWPC construction

In a multi-wire proportional chamber detector(MWPC), the anode and signal wires must maintain suitable tension, which is very important for the detector's stable and accurate performance. As a result, wire tension control and measurement is essential in MWPC construction. A high pressure3 He MWPC detector is to be used as the thermal neutron detector of the multi-functional reflectometer at China Spallation Neutron Source, and in the construction of the detector, we have developed a wire tension measurement system. This system is accurate,portable and time-saving. With it, the wire tension on an anode wire plane has been tested. The measurement results show that the wire tension control techniques used in detector manufacture are reliable.     

平面丝阵负载Z箍缩内爆动力学一维图像诊断

利用可见光条纹相机对单排和双排平面丝阵内爆动力学过程诊断中的初步实验结果,并对其进行了分析. 实验结果表明,单排平面丝阵相邻单丝等离子体之间并不是发生完全非弹性碰撞,部分等离子体会越过丝阵平面在中心形成先驱等离子体柱;双排平面丝阵中流过外部丝的电流要比内部丝大,烧蚀过程占整个内爆时间约65%,且只有部分质量参与了内爆过程. 关键词： 条纹相机 平面丝阵 Z箍缩 内爆动力学     

Design of a neutron-TPC prototype and its performance evaluation based on an alpha-particle test

A neutron-TPC(n TPC)is being developed for use as a fast neutron spectrometer in the fields of nuclear physics,nuclear reactor operation monitoring,and thermo-nuclear fusion plasma diagnostics.An n TPC prototype based on a GEM-TPC(Time Projection Chamber with Gas Electron Multiplier amplification)has been assembled and tested using argon-hydrocarbon mixture as the working gas.By measuring the energy deposition of the recoil proton in the sensitive volume and the angle of the proton track,the incident neutron energy can be deduced.A Monte Carlo simulation was carried out to analyze the parameters affecting the energy resolution of the n TPC,and gave an optimized resolution under ideal conditions.An alpha particle experiment was performed to verify its feasibility,and to characterize its performance,including energy resolution and spatial resolution.Based on the experimental measurement and analysis,the energy resolution(FWHM)of the n TPC prototype is predicted to be better than 3.2%for 5 Me V incident neutrons,meeting the performance requirement(FWHM5%)for the n TPC prototype.     

Z箍缩等离子体高分辨X辐射谱诊断

 为了获取丝阵Z箍缩等离子体高能谱分辨的X辐射图像,建立了云母球面弯晶X光摄谱仪,根据色散平面内球面弯晶诊断空间分布X光源的几何模型分析了摄谱仪的能谱分辨,计算结果与光线追迹方法得到的结果吻合。当探测器位于罗兰圆上时,系统具备最优能谱分辨。在“强光一号”装置上,利用该摄谱仪诊断了镀镁铝丝阵负载Z箍缩等离子体的X辐射图像,结果表明,该球面弯晶摄谱仪的能谱分辨率高于1 000。