Hard x-rays generated by bremsstrahlung from low-energy electrons have a wide distribution of emission angles, which inherently limits radiation utilization efficiency. This study proposes a Compton-scattering-based augmentation technique that increases utilization efficiency by partially scattering laterally escaping photons into the detection region and reducing their average energy. The augmentation characteristics of various Compton scattering layer (CSL) materials and geometries were analyzed theoretically, validated numerically, and used to establish a practical selection method for CSL design. A graphite CSL tailored for a cylindrical virtual-cathode reflex triode array was developed and experimentally tested. The experimental data show a 13.9% increase in radiation utilization efficiency-consistent with the 13.5% predicted by simulation-and a 28.4% increase in uniform-dose area.

Diode is one of the most important elements in the excimer laser, which is used to generate and accelerate electron beams to pump laser. Traditional large-area electron beam diodes for excimer laser pumping rely on guiding magnetic fields to confine the electron beam, which increases system volume and complexity and limits modularization. This paper presents and validates a magnetic-field-free modular array diode. Driven by modular pulsed power units and employing strip-shaped array cathodes, the diode is designed by combining field-enhanced space-charge-limited flow theory with particle-in-cell simulations. This approach optimizes the matching between the cathode width and the anode hibachi aperture to minimize beam interception on the grid and achieve impedance matching of ∼50 Ω with the driver. At an accelerating voltage of 150 kV, experiments demonstrate an electron beam energy deposition efficiency of 38.2% and a beam transport efficiency of 39.5%, with deviations of less than 10% from Monte Carlo simulations. This method provides a universal framework for designing efficient and compact electron beam diodes under magnetically unconfined or weakly confined conditions, paving a promising path toward advanced high-power excimer lasers for inertial confinement fusion.

The cylindrical virtual cathode reflex triode (CVCRT) is a new type of pulsed hard x-ray load characterized by high radiation conversion efficiency and a simple structure. When connected in series or parallel as an array, it can generate a high-fluence, large-area, uniform hard x-ray field. Numerical simulation is an important technical approach for the design and regulation of the radiation field of CVCRT arrays. However, due to the multitude of involved physical processes and the complex electromagnetic, particle, and radiation environments, the original simulations of radiation field intensity exhibit significant discrepancies compared to experimental results. This study presents modifications to the original simulation method: a phased modeling approach for the array load operation was adopted, incorporating the influence of cathode plasma expansion on the impedance load characteristics. Electron energy loss verification was performed across different models, and the spatial superposition method for the radiation field was refined. Consequently, a new simulation methodology for the radiation field of CVCRT arrays was established. Compared with experimental data, the mean relative error for the simulated photon fluence was 7.0%, and the simulation accuracy of the radiation field intensity was significantly enhanced compared to the original simulation method. This improved simulation method provides a more accurate basis for the design of CVCRT array-type loads.

We have designed, assembled, and tested a 4-MA, 60-ns fast linear transformer driver (LTD), which is the first operating generator featuring multiple LTD modules connected in parallel. The LTD-based accelerator comprises six modules in parallel, each of which has ten-stage cavities stacked in series. The six LTD modules are connected to a water tank of diameter 6 m via a 3-m-long impedance-matched deionized water-insulated coaxial transmission line. In the water tank, the electrical pulses are transmitted down by six horizontal tri-plate transmission lines. A 2.1-m-diameter two-level vacuum insulator stack is utilized to separate the deionized water region from the vacuum region. In the vacuum, the currents are further transported downstream by a two-level magnetically insulated transmission-line and then converged through four post-hole convolutes. Plasma radiation loads or bremsstrahlung electron beam diodes serve as loads that are expected to generate intense soft X rays or warm X rays. The machine is 3.2 m in height and 22 m in outer diameter, including support systems such as a high-voltage charge supply, magnetic core reset system, trigger system, and support platform for inner stalk installation and maintenance. A total of 1440 individual ±100-kV multi-gap spark switches and 2880 individual 100-kV capacitors are employed in the accelerator. A total of 12 fiber-optic laser-controlled trigger generators combining photoconductive and traditional gas spark switch technologies are used to realize the synchronous discharge of the more than 1000 gas switches. At an LTD charge voltage of ±85 kV, the accelerator stores an initial energy of about 300 kJ and is expected to deliver a current of 3–5 MA into various loads. To date, the LTD facility has shot into a thick-walled aluminum liner load and a reflex triode load. With a thick-walled aluminum liner of inductance 1.81 nH, a current with peak up to 4.1 MA and rise time (10%–90%) of about 60 ns has been achieved. The current transport efficiency from the insulator stack to the liner load approaches 100% during peak times. The LTD accelerator has been used to drive reflex triode loads generating warm X rays with high energy fluence and large radiation area. It has been demonstrated that this LTD is a promising and high-efficiency prime pulsed power source suitable for use in constructing the next generation of large-scale accelerators with currents of tens of megaamperes.

The cylindrical virtual cathode reflex triode is a new type of pulsed hard X-ray load, which has the advantages of simple structure, high radiation conversion efficiency, and simplicity in seriesparallel operation. This paper presents a method to reduce the impedance of the triode using a multiring cathode. The average electric field on the ring-cathode emission surface is enhanced due to edge effect, and the beam intensity is greatly increased in proportion to the square of the electric field strength. Multi-ring cathode is used to enlarge the emission area. Therefore, the reflex triode can work at lower impedance and generate a stronger beam under the same anode-cathode gap. In addition, the electric field enhancement of the cathode reduces the cathode emission stabilization time and enhances the operation stability of the triode. The effects of parameters such as ring width and ring gap on the triode impedance are simulated and studied. The cathode emission stabilization time and the X-ray conversion efficiency are compared. The design basis of cathode structure parameters and the impedance control method of the cylindrical virtual cathode reflex triode are given according to the simulations.

The bremsstrahlung cylindrical virtual cathode reflex triode (CVCRT) array is a new type of pulsed warm X-rays load. In this article, we established the CVCRT particle model and simulated and analyzed the working process and the influence of structural parameters on impedance. The results show that the impedance of the CVCRT depends on the structure of electrode and the thickness of anode conversion target. The theoretical impedance calibration relation was given, and the impedance simulation results of particle simulation agree well with the theoretical solution. Based on the Monte Carlo (MC) code, the radiation model of the CVCRT was established, and the influence rule of anode conversion target on X-ray parameters was studied. Results show that the anode thickness is the main factor affecting X-ray intensity. Under the voltage of 300 kV, the optimum thickness of the anode is about $10~\mu \text{m}$ . The influence of array arrangement on the spatial distribution of radiation field was calculated. The CVCRT array can superpose the X-rays in the effective radiation region and improve the efficiency of X-ray utilization, and the intensity of X-rays is about 1.9 times higher than that of the cylindrical reflex triode (CRT) under the identical driving conditions.

A cylindrical reflex triode was designed and directly driven by a four-stage linear transformer driver to generate high intensity pulsed warm x rays. We developed a numerical model of the cylindrical reflex triode and simulated and studied the experimental electron distribution and the radiation characteristics. The working voltage of the cylindrical reflex triode is 220 kV, and the current is about 600 kA. Under the voltage pulse with a rise time of 100 ns, the electron beam spot is uniform, and the duration of the gap without short circuit reaches 200 ns. The x-ray dose is 385 rad (Si), with an irradiation area of 615 cm2 and a uniformity of less than 2:1. The radiation field distribution is basically consistent with the simulation results. Compared with the two-stage series diode on the Flash-II accelerator, the x-ray conversion efficiency of the cylindrical reflex triode is increased about 1.6 times.

介绍了利用串级二极管产生高强度脉冲硬X射线的方法及其辐射场参数.以"闪光二号"加速器为平台,通过适应性改造,产生快前沿电压脉冲;研制了两级阻抗1 Ω串级二极管,通过串联分压降低二极管端电压、各级二极管电子束独立打靶在空间叠加形成高强度均匀辐射场.解决了悬浮电极绝缘支撑、二极管阴极均匀发射等技术难题,实现了串级二极管的稳定工作.在总电压约700 kV、电流约310 kA条件下,X射线平均能量87 keV,500 cm2上的平均能注量36 mJ/cm2,剂量均匀性(最大值比最小值)达到2:1.

介绍了基于吸收法的脉冲硬X射线能谱测量的基本原理及设计思路,完成了探测器及吸收片的选型,设计了射线准直系统,研究了散射对测量的影响,以12路PIN探测器阵列及铜、铝吸收片为测量核心部件研制了脉冲硬X射线能谱测量系统.实验测量了真空环境下"闪光二号"加速器串级二极管产生的脉冲硬X射线强度,获得了不同衰减程度的实验波形,通过解谱获得了脉冲硬X射线的能谱,光子最高能量约600 keV,平均能量约89.1 keV,与理论计算的结果比较符合.

环形阴极是一种结构场增强型阴极,能有效提高电子发射性能,广泛应用于脉冲硬X射线负载、强流电子束装置及高功率微波系统中,对其宏观场增强效应计算研究具有重要意义.本文采用电荷等效法和镜像法相结合的方法,建立阴阳极间隙空间电场的理论计算模型,获得阴极表面电场分布及其宏观场增强因子,并拟合给出宏观场增强因子的经验估算公式.计算结果表明,当阴阳极间隙与阴极环宽之比(d/w)<5,环形阴极宏观场增强因子与d/w呈良好的线性关系,理论计算结果与Ansoft软件模拟结果基本一致.

Pulsed high-energy fluence X-ray source is based on the "Flash II" accelerator. It can be used to carry out effect vulnerability and sensitivity test of unit level system generated electromagnetic pulse (SGEMP). The energy fluence of pulsed hard X-ray is a main parameter of the equipment beam. At present, theoretical calculation method is widely used. Energy fluence can be calculated according to the dose, energy spectrum and energy absorption coefficient of each energy segment. The principle measuring energy fluence of pulsed hard X-ray by total absorption method is introduced. The photoelectric cell with lutetium silicate (LSO) scintillator is selected as a core component of the detection system, and the measurement system is developed. It is composed of scintillation detector, LSO scintillator, dimmer film, photon collimator, visible light shielding material, power supply and signal collecting system. The conversion coefficient between the incident photon energy and the waveform parameter is calibrated by a standard X-ray source. The energy fluence measurement experiment is carried out with the high-energy beam source of the "Flash II" accelerator as an experimental platform. In order to meet the requirements of the effect test experiments, the series diode structure is used in the accelerator for forming a high strength and large area uniform X-ray source. In the experiment, the LiF TLD is located in the front of the phototube and used to monitor the dose. According to the measured waveform, the actual energy of the incident photons is calculated. Combined with the receiving area of incident photons, the energy fluence of pulsed hard X-ray is calculated. The average measured value is 35.9 mJ/cm(2) in 5 consecutive experiments. Energy fluence calculated from the measured dose and energy spectrum is 39.8 mJ/cm(2). The results of the two methods are compared. It can be found that the experimental result is about 9.8% smaller than the theoretical value. The reasons are as follows. According to the law of exponential decay of rays in matter, in fact, the scintillator cannot absorb all the rays, and some of the rays can penetrate through, the energy of these rays cannot be detected, and thus giving rise to small experimental value. Due to the limited energy point of quasi-monoenergetic source, the sensitivity under the mean photon energy is taken as the sensitivity of the detector, and therefore there is a certain degree of uncertainty. The successful application of the measurement technology provides a good experimental method for the following similar research, and can also provide a reference for X-ray intensity analysis.

An electrical wire explosion is a complicated process consisting of several physical phenomena such as acoustic, optical, mechanical, electromagnetic, and thermal phenomena. The shock wave from such an explosion not only has a wide range of practical applications but it also plays an important role in analyzing the process of the explosion itself. In this paper, we propose an empirical approach to estimate the pressure and energy of the shock wave in an underwater electrical wire explosion. First, the discharge process is divided into several typical phases, and the deposited electrical energy, power, and time interval between adjacent phases are calculated. Then, the shock wave peak pressure is measured and the total mechanical energy is calculated, respectively. Finally, a multiparameter fitting method is adopted to deduce an empirical formula for peak pressure and shock wave energy, and the formula was the exponential function of the deposited electrical energy, power, and the discharge time interval. In this way, the shock wave pressure and energy are quickly and reliably estimated for given discharge parameters. As for 155 shots of the discharge experiment, the average relative error and the standard deviation of peak pressure are 8.45% and 5.47%, respectively, and those of the shock wave energy of are 12.2% and 11%, respectively. This empirical approach would be very useful in pulsed power device design and in the parameters involved in electrical wire matching.

This paper presents a method for moderate pulsed X rays produced by a series diode, which can be driven by high voltage pulse to generate intense large-area uniform sub-100-keV X rays. A two stage series diode was designed for Flash-II accelerator and experimentally investigated. A compact support system of floating converter/cathode was invented, the extra cathode is floating electrically and mechanically, by withdrawing three support pins several milliseconds before a diode electrical pulse. A double ring cathode was developed to improve the surface electric field and emission stability. The cathode radii and diode separation gap were optimized to enhance the uniformity of X rays and coincidence of the two diode voltages based on the simulation and theoretical calculation. The experimental results show that the two stage series diode can work stably under 700 kV and 300 kA, the average energy of X rays is 86 keV, and the dose is about 296 rad(Si) over 615 cm2 area with uniformity 2:1 at 5 cm from the last converter. Compared with the single diode, the average X rays' energy reduces from 132 keV to 88 keV, and the proportion of sub-100-keV photons increases from 39% to 69%.

研制了一台200 kV/200 kA脉冲源,脉冲源由初级储能单元、水介质整形与传输单元、气体开关和负载组成.通过优化设计由2Ω到1Ω的水介质变阻抗线、高压气体主开关和陡化开关,使得脉冲功率源在匹配负载下产生输出电压200 kV、电流200 kA、前沿40 ns、脉宽40 ns的高压脉冲.在此脉冲源平台上已开展了低阻抗1Ω二极管发射特性研究,并且将在高压气体开关、同步触发、二极管等离子体发射诊断等方面发挥作用.

This paper presents the approximate analytic solutions of current density for annulus and circle cathodes. The current densities of annulus and circle cathodes are derived approximately from first principles, which are in agreement with simulation results. The large scaling laws can predict current densities of high current vacuum diodes including annulus and circle cathodes in practical applications. In order to discuss the relationship between current density and electric field on cathode surface, the existing analytical solutions of currents for concentric cylinder and sphere diodes are fitted from existing solutions relating with electric field enhancement factors. It is found that the space-charge-limited current density for the cathode with electric-field enhanced geometry can be written in a general form of J = g(βE)2J0, where J0 is the classical (1D) Child-Langmuir current density, βE is the electric field enhancement factor, and g is the geometrical correction factor depending on the cathode geometry.

采用高纯石墨环状阴极和有机玻璃绝缘子,研制了一套低阻抗大面积二极管系统.使用理论计算和数值模拟方法对二极管进行优化设计,在保证绝缘要求的同时,尽量优化二极管轴向长度和内外筒距离以减小二极管的回路电感.实验结果表明,优化后的二极管能在200 kV左右的电压上稳定工作,绝缘结构未发生击穿现象;实验中最高输出电压为213 kV,电流为221 kA,特性阻抗约为1 Ω,电流密度为8 kA/cm2,脉宽(FWHM)为50 ns.

介绍了利用串级二极管产生大面积脉冲硬X射线的基本原理,建立了串级二极管的等效电路模型,分析了二极管串联工作过程,通过模拟计算给出了串级二极管工作过程的影响因素.串级二极管分压过程分为电容分压、阻抗和容抗分压、真空击穿后动态平衡及阻抗分压四个阶段,二极管电容和真空击穿电压是影响二极管串联初始阶段分压的主要因素,二极管的阻抗变化过程和二极管间隙的击穿时间差决定二极管分压的一致性.

针对系统电磁脉冲效应研究需求,项目组对“闪光二号”加速器进行了适应性改造,以便于产生脉冲硬X射线.主要采用二次成形的水线结构,重点进行了水开关设计,并完成了实验调试.装置输出电压650 kV～1.3 MV稳定可调,脉冲宽度60 ns,前沿由改造前的80 ns缩短至改造后的30 ns,在国内首次成功驱动串级二极管,产生前沿29 ns、射线宽度约53 ns的脉冲硬X射线.

Cathode plasma of high current electron beam diode is an important research on high power microwave and strong pulsed radio accelerator. It is a reliable method to study cathode plasma by diagnosing the cathode plasma parameters with non-contact spectroscopy measurement system. The present paper introduced the work principle, system composition and performance of the nanosecond (ns) time-resolved spectroscopy diagnosis system. Furthermore, it introduced the implementing method and the temporal relation of lower jitter synchronous trigger system. Simultaneously, the authors designed electromagnetic and radio shield room to protect the diagnosis system due to the high electromagnetic and high X-ray and γ-ray radiation, which seriously interferes with the system. Time-resolved spectroscopy experiment on brass (H62) cathode shows that, the element and matter composition of cathode plasma is clearly increase with the increase in the diode pulsed voltage and current magnitude. The spectroscopy diagnosis system could be of up to 10 ns time resolve capability. It's least is 2 ns. Synchronous trigger system's jitter is less than 4 ns. The spectroscopy diagnosis system will open a new way to study the cathode emission mechanism in depth.