A neutron camera system for MAST

A prototype neutron camera has been developed and installed at MAST as part of a feasibility study for a multichord neutron camera system with the aim to measure the spatial and time resolved 2.45 MeV neutron emissivity profile. Liquid scintillators coupled to a fast digitizer are used for neutron/gamma ray digital pulse shape discrimination. The preliminary results obtained clearly show the capability of this diagnostic to measure neutron emissivity profiles with sufficient time resolution to study the effect of fast ion loss and redistribution due to magnetohydrodynamic activity. A minimum time resolution of 2 ms has been achieved with a modest 1.5 MW of neutral beam injection heating with a measured neutron count rate of a few 100 kHz.     

Diagnostics for ion beam driven high energy density physics experiments

Intense beams of heavy ions are capable of heating volumetric samples of matter to high energy density. Experiments are performed on the resulting warm dense matter (WDM) at the NDCX-I ion beam accelerator. The 0.3 MeV, 30 mA K(+) beam from NDCX-I heats foil targets by combined longitudinal and transverse neutralized drift compression of the ion beam. Both the compressed and uncompressed parts of the NDCX-I beam heat targets. The exotic state of matter (WDM) in these experiments requires specialized diagnostic techniques. We have developed a target chamber and fielded target diagnostics including a fast multichannel optical pyrometer, optical streak camera, laser Doppler-shift interferometer (Velocity Interferometer System for Any Reflector), beam transmission diagnostics, and high-speed gated cameras. We also present plans and opportunities for diagnostic development and a new target chamber for NDCX-II.     

Development of a simultaneous Hugoniot and temperature measurement for preheated-metal shock experiments: melting temperatures of Ta at pressures of 100 GPa

Equations of state of metals are important issues in earth science and planetary science. A major limitation of them is the lack of experimental data for determining pressure-volume and temperature of shocked metal simultaneously. By measuring them in a single experiment, a major source of systematic error is eliminated in determining from which shock pressure release pressure originates. Hence, a non-contact fast optical method was developed and demonstrated to simultaneously measure a Hugoniot pressure-volume (P(H)-V(H)) point and interfacial temperature T(R) on the release of Hugoniot pressure (P(R)) for preheated metals up to 1000 K. Experimental details in our investigation are (i) a Ni-Cr resistance coil field placed around the metal specimen to generate a controllable and stable heating source, (ii) a fiber-optic probe with an optical lens coupling system and optical pyrometer with ns time resolution to carry out non-contact fast optical measurements for determining P(H)-V(H) and T(R). The shock response of preheated tantalum (Ta) at 773 K was investigated in our work. Measured data for shock velocity versus particle velocity at an initial state of room temperature was in agreement with previous shock compression results, while the measured shock data between 248 and 307 GPa initially heated to 773 K were below the Hugoniot evaluation from its off-Hugoniot states. Obtained interfacial temperatures on release of Hugoniot pressures (100-170 GPa) were in agreement with shock-melting points at initial ambient condition and ab initio calculations of melting curve. It indicates a good consistency for shock melting data of Ta at different initial temperatures. Our combined diagnostics for Hugoniot and temperature provides an important approach for studying EOS and the temperature effect of shocked metals. In particular, our measured melting temperatures of Ta address the current controversy about the difference by more than a factor of 2 between the melting temperatures measured under shock and those measured in a laser-heated diamond anvil cell at ～100 GPa.     

Measurement technology for material emissivity under high temperature dynamic heating conditions

The thermal dissipation of radiation is main heat shield mechanism for non-ablative thermal protection materials on hypersonic vehicles withstanding high temperature dynamic heating cycle during endo-atmospheric ascent, cruise and reentry. Therefore, it is necessary to know the thermal radiative properties of the material under the simulated high temperature dynamic heating conditions on the ground. The emissivity depends on the surface state and its temperature. A new simultaneous measurement technology of emissivity and varying surface temperature is proposed under high temperature dynamic heating conditions. This new technology solved synchronous measurement problems by utilizing spectral signal of Fourier transform infrared (FTIR) spectroscopy. The calibration of different temperature ranges, the background disturbances, the influences on temperature measurement by wavelength range and its corresponding fluctuations of measurement signal, were thoroughly investigated. The measured results of steel and graphite as reference materials proved the effectiveness of this simultaneous measurement technology and showed great potential in engineering applications under high temperature dynamic heating conditions.     

利用信号拼接提高调频连续波激光测距系统的分辨力

提出了一种对等频率间隔的采样信号进行拼接来提高调频连续波激光测距系统的测距分辨力的方法。研究了调频连续波激光测距的原理,设计搭建了基于一种双干涉系统的光纤调频连续波激光测距系统。利用辅助干涉系统产生的时钟信号对测量干涉系统的信号进行等光频间隔的采样,然后对采样信号进行拼接。使用LabVIEW设计了信号错误检测处理、采样和拼接的信号处理系统。利用该测距系统进行了实验验证,结果显示,将等光频间隔的采样信号进行拼接的方法可以突破激光器扫描范围的限制,减少光源非线性的影响,从而提高系统的测距分辨力。得到结果表明,在测量距离为8.7m时,该系统的测距分辨力可达70μm,30组测量结果的重复性标准差为35μm。     

方酸衍生物的三阶非线性光学特性

采用波长为800 nm、脉宽为50 fs的激光系统,运用双光束前向简并四波混频技术(DFWM)研究了两种方酸衍生物的三阶非线性光学特性,并探讨了它们的非线性形成机制。实验测得所研究的两种方酸衍生物的分子超极化率γ值均为~10^-31 esu,其非线性光学响应时间小于激光脉宽(50 fs)。因而,所研究的方酸衍生物有较大的三阶非线性光学性质和较快的光学响应,在光学器件中具有潜在的应用价值。     

A radiation foil bolometer for measuring the energy losses of fast Z-pinches

A radiation foil bolometer intended for measuring radiation-energy fluxes and plasma flows in high-power pulsed plasma X-ray sources is studied. In the bolometer, the radiation or ion-flow energy is absorbed by a 13-μm-thick niobium foil preliminarily heated to T ≈ 1900 K by a quasi-constant current lasting 2 s. Radiation from the foil was fed through an 8-m-long light guide to a semiconductor photodetector. The sensitivity of the instrument obtained from the results of calibrations is 0.56 J/V cm². The time resolution of this technique (∼2.5 μs) is determined by the foil heating time. In experiments with megaampere Z-pinches, the time resolution attained allows detection of the radiation energy independently of the energy of expanding plasma flows. In this case, the photoelectric effect from X-rays and the conductivity of expanding plasma do not affect the operation of the radiation bolometer. The working capacity of the bolometer was demonstrated at the Angara-5-1 facility in experiments with high-current Z-pinches with a radiation output energy of 50–100 kJ/pulse. The measurements performed have shown that the energy flux density of plasma expanding in the direction perpendicular to the pinch axis is at most 5% of the energy flux density of soft X-rays.     

Development of an improved method for investigating the frictional properties of lubricants under transient EHD conditions

In the design and evaluation of mechanical system performance it is important to know the frictional qualities of the lubricant. Without correct numerical treatment of the lubricant during simulations of large systems, e.g., drive trains in trucks and buses, the results will, to a large extent, be inaccurate. However, obtaining detailed information places demands on the test equipment as the events are both transient and highly loaded. Under quasi‐static conditions, forces are measured with force transducers, but in elasto‐hydrodynamically lubricated conjunctions, where pressures are so high that the surrounding surfaces deform elastically, this cannot be done without permanently damaging the equipment. The conceptual design of the test equipment must therefore incorporate the measuring process in transient conditions (loading‐unloading times of 200–500 μs) being performed in real time, and allow extreme pressures of up to 3 GPa without component destruction. One way to obtain accurate friction data successfully is to apply a concentrated force pulse to a non‐instrumented surface and to measure the response from that pulse elsewhere. The development of a measurement technique, the Lulea ball and bar apparatus, which utilises wave propagation theory, is presented in this paper. An oblique impact on a robust end plate on a rod was used to generate both non‐dispersive compression waves and dispersive flexural waves. The normal force created by the axial wave was measured using strain gauges, while the transverse force was derived from the fast Fourier transforms of two lateral acceleration histories, using dynamic beam theory. The relation between the normal and tangential force histories showed the frictional properties at the impact as a function of time. A variety of lubricants was also studied at Hertzian pressures of up to 2.5 GPa, and the development of the method and results are presented. Experiments indicate that different lubricants exhibit different frictional properties and that the resolution in the test equipment is sufficient to indicate this.     

桌面97单元自适应光学系统性能测试

构建了一套桌面自适应光学系统性能测试系统,用以验证97单元自适应光学系统的校正能力。该测试系统主要由光源、快速控制反射镜、变形镜、Shack-Hartmann波前传感器、高速波前处理器、扰动相位屏等部件组成,分别利用干涉仪和Shack-Hartmann波前传感器的数据控制变形镜进行光路的展平校正,得到了系统的静态校正精度。然后,测试了精密跟踪系统的校正能力。最后,利用扰动相位屏模拟不同的大气扰动条件,以成像相机图像的斯特列尔比(SR)为指标,在不同目标亮度下测试了自适应光学系统的动态校正能力。测试结果显示:该97单元自适应光学系统的静态波像差校正精度的RMS接近λ/20;两种控制模式下精密跟踪系统的误差抑制带宽分别达到了15 Hz和39 Hz;系统在强湍流情况下,动态校正后的成像分辨率基本优于3倍衍射极限。由此表明,97单元自适应光学系统能够有效地校正像差,提高成像分辨率。     

Far field resolution beyond the Abbe limit using photodiffraction

In this paper we show how a tightly focused pump beam can be used to alter the local refractive index of the sample. This local variation acts as a scattering site, which enables resolution exceeding that of a conventional scanning microscope to be obtained in the far field. The improvement in resolution depends on a number of factors which are discussed in the paper, including the optical configuration (confocal or non-confocal), the thermal properties of the sample, the 'strength' of the object and the duration of the heating pulse. Experimental results confirming the theoretical predictions are presented; these demonstrate more than 25% improvement in edge response compared with a conventional scanning system.     

An automated tracking system to measure the dynamic properties of vesicles in living cells

Recent technological improvements have made it possible to examine the dynamics of individual vesicles at a very high temporal and spatial resolution. Quantification of the dynamic properties of secretory vesicles is labor-intensive and therefore it is crucial to develop software to automate the process of analyzing vesicle dynamics. Dual-threshold and binary image conversion were applied to enhance images and define the areas of objects of interest that were to be tracked. The movements, changes in fluorescence intensity, and changes in the area of each tracked object were measured using a new software system named the Protein Tracking system (PTrack). Simulations revealed that the system accurately recognized tracked objects and measured their dynamic properties. Comparison of the results from tracking real time-lapsed images manually with those automatically obtained using PTrack revealed similar patterns for changes in fluorescence intensity and a high accuracy (<89%). According to tracking results, PTrack can distinguish different vesicular organelles that are similar in shape, based on their unique dynamic properties. In conclusion, the novel tracking system, PTrack, should facilitate automated quantification of the dynamic properties of vesicles that are important when classifying vesicular protein locations.     

A diamond-detector-based system for spectrometry of fast atoms on the JET tokamak

To study the evolution of the distribution function of fast ions with an ultimately high time resolution during both injection of neutrals and ion cyclotron plasma heating on the JET tokamak, we have developed a system for spectrometry of fast charge-exchange atoms, which consists of a spectrometric natural-diamond detector and a digital spectrometric channel. The main elements of the spectrometric system—the diamond detector, a noise-immune charge-sensitive preamplifier, and a fast analog-to-digital converter (ADC)—have been manufactured explicitly for use in spectrometry of fast charge-exchange atoms on the JET tokamak at high counting rates. The diamond detector that ensures the spectrometry of hydrogen atoms in the energy range 20–5000 keV is installed in the equatorial plane at an 18-m distance from the plasma axis at the end of the vacuum channel created for X-ray spectroscopy. A fast 14-bit ADC with 100-MHz sampling frequency and a 2-GB memory digitizes the preamplifier output signal. The developed digital spectrometric system can operate at a counting rate of up to ～10⁷ counts/s. Laboratory tests of the developed spectrometric system have shown that its energy resolution is no worse than the resolution of a similar analog system. In the experiments on the JET, the diamond digital spectrometric system ensures recording of the energy distributions of fast charge-exchange atoms with energies >40 keV.     

高分辨掠入射软X射线-真空紫外单色仪

介绍了用于束箔光谱实验中研制的一台高分辨掠入射软X射线-真空紫外单色仪基本原理及仪器组成,给出了仪器性能的测试及初步实验结果。     

红外高光谱干涉仪辐射定标误差敏感性因子的仿真分析

鉴于对高精度高时空分辨率大气探测资料日益增长的科研和业务需求,我国正大力发展星载红外高光谱探测系统。星载红外高光谱干涉仪光机结构复杂,仪器状态会显著影响其定标精度。本文通过理论分析和仿真实验,分别讨论了内黑体发射率、低温黑体发射率、内黑体与环境温度差、非线性系数以及直流电压演算等误差敏感性因子影响辐射定标精度的特征。分析表明定标辐射偏差的绝对值与内黑体/低温黑体发射率呈线性关系,且与内黑体与环境温度差、非线性系数、直流电压呈正相关;提高内黑体发射率和低温黑体发射率到0.985以上、控制内黑体与环境温度差在0.6 K左右、控制干涉仪的非线性效应系数低于0.04,这些方案均是实现0.1 K辐射定标精度的必要条件;辐射定标参数对定标辐射的影响特征结合地面真空实验的定标参数估计,可以迭代得到已测得和未知的定标参数的最优估计,从而提高定标精度。本文的研究结果对于红外高光谱干涉仪的参数设计以及辐射定标误差来源的识别和订正有着十分重要的意义。     

多通道门选通纳秒分幅相机

采用光学分幅技术和多通道门选通法研制了纳秒分幅相机。首次应用八棱锥将图像分为8幅,每幅图像有相等的光学能量并包含与原图像相同的光学信息,每个通道使用独立的带门选通的像增强器和CCD相机,自行开发的近贴门选通像增强器用于增强弱光图像。相机系统可一次获得8幅图像,分幅速率达到1×10⁸ frame/s,最短曝光时间和时间间隔为3 ns和10 ns并分别可调,可记录持续时间为百纳秒到几十微秒的发光现象,动态空间分辨率达到15 lp/mm。该相机已成功应用于电脉冲、等离子发光等现象的试验并获得了有意义的数据,可满足高速摄影机等设备具有高分幅速率,短曝光时间和适当间隔以及在曝光时间内固定时刻记录超快现象过程的要求。     

飞轮组件微振动对高分辨率光学卫星光轴的影响

为了研究高分辨率光学卫星星上飞轮的微振动对卫星成像质量的影响,分别建立了飞轮扰动模型和整星结构动力学模型。首先,对飞轮组件系统进行了地面扰动测试,对实测扰动数据的分析表明,飞轮组件在与转速相关的一阶频率50Hz处产生一次谐波,在190Hz与280Hz左右存在与转速无关的一系列峰值。然后,对整星进行了单位正弦激励,获得了光轴角位移响应,并对其与飞轮实测扰动数据进行了集成分析。分析结果表明:整星在50~80 Hz和230~280Hz的角位移响应有较多的谐振响应频率成分,沿光轴方向和垂直光轴方向整星光轴的角位移最大谐振响应幅值分别为2.718″、2.739″,在245Hz左右存在较多幅值为0.5″量级的谐波。分析显示飞轮组件微振动对高分辨率光学卫星成像质量影响较大,得到的结果可为整星系统的优化设计和隔振补偿措施提供参考依据。     

Development of a realistic photonic modeling for the evaluation of infrared reflections in the metallic environment of ITER

In nuclear fusion experiments, the plasma facing components are exposed to high heat fluxes and infrared (IR) imaging diagnostics are routinely used for surveying their surface temperature for preventing damages. However the future use of metallic components in the ITER tokamak adds complications in temperature estimation. Indeed, low and variable emissivity of the observed surface and the multiple reflections of the light coming from hot regions will have to be understood and then taken into account. In this paper, a realistic photonic modeling based on Monte Carlo ray-tracing codes is used to predict the global response of the complete IR survey system. This also includes the complex vessel geometry and the thermal and optical surface properties using the bidirectional reflectivity distribution function that models the photon-material interactions. The first results of this simulation applied to a reference torus are presented and are used as a benchmark to investigate the validity of the global model. Finally the most critical key model parameters in the reflected signals are identified and their contribution is discussed.     

A fast time-response bolometer for soft X-ray radiation energy measurements in a high-current Z-pinch

A high-sensitivity bolometer with a short time response to heating with external radiation has been developed. It is intended for measuring the integral parameters of soft X-ray radiation of liner plasma. The bolometer is adapted to the conditions of explosion experiments with an increased level of electromagnetic pickups at facilities that are based on magnetic-explosion generators with megaampere currents. The bolometer has a metal casing for improving the noise immunity of measurements. A 2-μm-thick nickel foil is used as the material for the resistive element of the working substance of the bolometer. The choice of the material and the geometrical dimensions of the bolometer working elements were analyzed. The ultimate thermal load on the bolometer was determined. A technique for calibrating the working elements using a pulse current was developed. The working capacity, good noise immunity, and a high sensitivity of the bolometer were demonstrated in experiments. The dynamic range in measurements of the surface energy density of X rays is 0.03–0.3 J/cm².     

用于位相缺陷检测的反射式剪切点衍射干涉仪

为了实现光学元件位相缺陷的大视场、高分辨率、瞬态检测,设计了一种基于无镜成像算法的反射式剪切点衍射干涉仪。该干涉仪通过在参考光与测试光之间引入横向错位量,形成高密度线性载频,利用快速傅里叶变换算法从单幅干涉图中提取待测波面信息,实现缺陷的瞬态测量。利用无镜成像算法抑制了缺陷的衍射效应,总结了有效的缺陷类型辨别方法。实验检测了强激光系统中的一块光学平晶,验证了所提缺陷类型判据的正确性。此外,采用反射式剪切点衍射干涉仪对一块激光毁伤的光学平板进行检测,测试结果与Veeco NT9100白光干涉仪测量结果相比,相对误差为2.1%。结果表明,该干涉仪能够有效应用于检测大口径光学元件的位相缺陷。     

A radiographic facility for the 70-GeV proton accelerator of the institute for high energy physics

A radiographic facility for the 70-GeV proton a ccelerator of the Institute for High Energy Physics is described. The available infrastructure in the initial straight part of the injection channel is used in the facility. The 100-mm-diameter lenses of the injection line ar e intended for transportation of the proton beam from the U-70 accelerator to the accelerating—storage complex. The facility has been designed only for an energy of 50 GeVwith a viewfield of 60 mm and used for imaging of samples with an optical density of >300 g/cm² in the presence of some losses in the line. The optical resolution of the facility is 0.25 mm. A set of experiments aimed at multiframe recording of fast processes were conducted on the facility in 2004-2008. Small-sized explosion-proof chambers, as well as the measuring system for monitoring the state of the chamber and environment, were used in the dynamic experiments.