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.

Abstract To investigate the light radiation process of metal wire electric explosion under various working conditions, a synchronous testing system was established using high-speed cameras, photocell tubes and other instruments to study the ultra-fine tantalum wire electric explosion process. The light radiation characteristics of tantalum wire electric explosion were analyzed under different input voltage, quantity, and length conditions. Results indicate that increasing the input voltage from 15kV to 21kV leads to an increase in relative light intensity emitted by the tantalum wire at measurement point 4 from 0.13V to 3.62V with an extension of luminescence process from 4.23ms to 8.42ms and the light saturation time decreases from 150 µs to 20.85 µs; Increasing the number of tantalum wires does not significantly affect luminescence time or saturation time but decreases light intensity at measuring point 4 when increased from two to twelve; When the length of tantalum wire increases from 54.5cm to 68cm, the light intensity generated during the explosion process decreases, the luminescence process changes from 307µs to 921µs, and the light saturation time extends from 23.52µs to 40µs. These experimental findings provide robust data support for further exploration into synchronous detonation technology for light-initiated explosive.

Numerical model for calculating convective gains and absolute thresholds of stimulated Raman scattering (SRS) in inhomogeneous plasmas is constructed based on the Fourier-space method. The model is valid for arbitrary density profiles and scattering geometries, including both backscattering and side scattering. It is shown that 90 deg side scatter has a lower absolute threshold than other scattering geometries. Backscatter, on the other hand, has a relatively large absolute threshold under conventional direct-drive ignition conditions. For a parabolic density profile, the absolute threshold of backscatter decreases dramatically at the peak of parabola, but is still much larger than that of side scatter. We also discuss the absolute thresholds of side scatter under different density profiles, showing not big differences with the linear density profile as well as the analytic formulas. Convective gains, however, are sensitive to the density profiles and collisional damping. The k-space numerical model is verified via analytic formulas and real-space envelope model, and it offers us new perspective on the scattering angles compared with previous models for SRS.

A transmission line circuit model was conducted to compare the performances of the two-level 2.5 Ω magnetically insulated transmission lines (MITLs) system of a 5-MA linear-transformer-driver (LTD) accelerator for two kinds of typical loads, including bremsstrahlung electron beam diodes and Z-pinch loads. Both the electron current loss in the pulse front during the magnetic insulation setup process and the electron flow distribution in the magnetic insulation steady state were analyzed. When the accelerator drives an electron beam diode load with impedance of 1.20 Ω (a single level), the duration of the magnetic insulation setup is about 12 ns, the current loss is about 130 kA in a single MITL level, the maximum electron flow current is about 50 kA in the end of MITL, and its amplitude decreases gradually after the steady magnetic insulation is established. When the accelerator drives a Z-pinch load with length of 1.5 cm, radius of 1.2 cm, and mass of 0.3 mg/cm, the duration of the magnetic insulation setup is almost zero, the maximum electron flow current in the end of MITL can reach about 55 kA (a single level), and the waveform of the electron flow resembles a saddle shape, which reaches the peak at the pinch stagnation time.

电爆炸等离子体的光辐射特性对探究非理想等离子体性质及含能材料点火技术具有重要意义.在过去几十年,国内外学者对电爆炸物理与效应开展了广泛研究,明确了等离子体及可见光辐射效应的典型特征规律.近年来,随着电爆炸技术在国防、能源和材料领域的逐步应用,人们开始关注电爆炸等离子体光辐射现象中更多的物理细节,以期实现电爆炸负载光辐射效应的有效调控.本文简要回顾了电爆炸负载及其光辐射效应的研究历程,并介绍了相关实验手段及技术原理.从动力学角度系统介绍了电爆炸等离子体及光辐射的时空演化行为,从光谱学角度分析了放电不同阶段的辐射光谱特性,建立了电爆炸关键过程和光辐射物理机制的对应性,归纳了放电模式、金属材质、介质类型对负载光辐射特性的影响.最后,探讨了基于强光辐射效应的电爆炸技术的发展趋势.

The physical image of the confined electrical explosion in the source region is depicted. Metallic plasma/vapor dynamics and its fragmentation effect (on a confining structure) under μs-timescale are diagnosed via high-speed photography, electrophysical, and spectral measurements. When adding a 1-mm-thick Teflon tube outside the exploding wire, the growth of spatial heterogeneity via electro-thermal instability is largely compressed, and the deposited energy almost doubled from about 85 to 150 J. During the short period after breakdown, considerable energy depositing into the confined space, e.g., 100 J for 0.1 cm3, drives the fast inflation and burst of the 0.5 g confining tube to ∼500 m/s (kinetic energy of ∼62.5 J). Intense plasma jet eruption with a supersonic speed >1.5 km/s and induced shock waves of 2–3 km/s are observed from cracks of the inflated tube. In addition, the erupted plasma jets gradually evolve Rayleigh–Taylor instability and finally cause turbulent mixing with the ambient medium. This mechanism is very likely to explain the plasma cavity evolution in underwater explosion. Interestingly, although the confining effect of water is stronger than a Teflon tube, the latter has a better response to the high-rate impulse loading and absorbs more deposited energy by deformation, phase transition, and acceleration.

In recent years, capillary discharge plasma has been popular in propulsion, fusion and other fields, and is usually regarded as a high heat flux source for material research. Metal wires are often selected as the ignition for capillary discharge because of the low ignition time dispersion. Focused on the phenomenon of radiation ablation, experiments were carried out to determine the evolution of metallic plasma jets and the mechanism of aluminum foil ablation. It was found that the placement of aluminum foil at the nozzle had little influence on capillary discharge, but more regular boundaries could be observed. The mechanism of aluminum foil burning and burning through was studied in terms of the radiation heat wave conduction, corresponding to “propagation” and “burn through” modes respectively.

利用金属丝电爆炸等离子体辐射强脉冲闪光驱动光敏炸药起爆，是开展强脉冲X射线热-力学效应研究的理想模拟加载方法之一，其关键问题是超长金属丝电爆炸的轴向光辐射均匀性。基于数字图像处理技术，建立了金属丝电爆炸等离子体光辐射均匀性定量化表征方法，分析了金属丝电爆炸沉积能量、金属丝材质和金属丝线质量密度分布等参数对其光辐射均匀性的影响规律。研究结果表明：沉积能量是影响金属丝电爆炸过程中光辐射均匀性的主要影响因素之一，在高脉冲功率源储能下，金属丝加载脉冲电流幅值高、上升时间快，其快速地沉积能量和欧姆加热过程有效提高了光辐射均匀性；其次，在欧姆加热阶段，难熔金属丝比易熔金属丝在电爆炸过程中更易获得均匀的轴向光辐射；最后，金属丝的线质量密度分布也会影响其光辐射均匀性，在质量密度不均匀处易形成较早的局部电爆炸，并产生强闪光点发射。

A 5-MA-LTD-based, high current accelerator is modeled using transmission line code. And the machine performances are presented for driving short-circuit loads, $Z$ -pinch loads, and bremsstrahlung electron beam diodes. With simulation analysis, it is expected that the short-circuit load current can reach 4.7 MA in 100 ns with ±80 kV LTD charge voltage, and the peak of $Z$ -pinch load current when the machine is conducted with a 0.45 mg wire-array can be high as 4.2 MA, the peak kinetic energy is 49 kJ, and the energy coupling efficiency is estimated as 38%. The physical model of the reflex triode load which is typical electron beam diode is presented in detail. By incorporating the physics-based reflex triode model into a 3-D transient electromagnetic model, the field-circuit coupling simulation can be performed and the results are compared with the circuit model. The results from these two methods are in good agreement. The peak load current when the machine is configured with a $\sim 0.15~\Omega $ reflex triode load is ~2.8 MA. The energy coupling efficiency to the reflex triode load is 35.8%.

液体中金属丝电爆炸(丝爆)不同于介质电击穿过程,涉及复杂金属相变,可产生具有更高能量效率的冲击波,已在化石能源开发等领域取得成功应用,也凸显出在地质勘探、矿山与安全工程等领域的巨大应用潜力.文中回顾了电爆炸冲击波技术的发展历程,基础研究方面分别从丝爆物理过程与冲击波产生机理、测量诊断和评估方法、冲击波特性与影响因素进行阐述,并从理论与实验角度提出了现阶段面临的科学问题与技术难点;应用研究方面简述了液体中丝爆在石化能源开发、物性研究装置、纳米材料制备等方面的应用与工程实践,给出了当前电爆炸冲击波技术在应用中亟待解决的瓶颈问题和方向.最后,归纳提出了该技术的发展趋势和路线图.

A 4 MV flash x-ray radiographic machine based on induction voltage adders has been developed. The configuration and design of this machine are reviewed. A three-dimensional, fully electromagnetic model and a circuit simulation model are established to compare with the experiments. The simulation results are in overall agreement with the electrical measurements. The pulsed power performances and output fluctuations of this machine over successive shot sequences are demonstrated. Among the 54 shots, the average peak output voltage is $4.4\ifmmode\pm\else\textpm\fi{}0.3\text{ }\text{ }\mathrm{MV}$ ($1\text{\ensuremath{-}}\ensuremath{\sigma}$) and the average diode current is $81.6\ifmmode\pm\else\textpm\fi{}4.5\text{ }\text{ }\mathrm{kA}$ ($1\text{\ensuremath{-}}\ensuremath{\sigma}$). Four typical malfunction modes are identified shot by shot including the diode-impedance collapse, insulator flashover, core saturation, and drive mistiming. Some remarkable features from each fault mode are recognized. The first-to-last time spreads of the four drive pluses, ${t}_{\mathrm{spread}}$, are chosen to quantify the drive synchronization and the influences of the ${t}_{\mathrm{spread}}$ on the peak voltages and diode currents are summarized from the almost 100 shots since the machine was commissioned. It is found that, in order to achieve a voltage of up to 4 MV, ${t}_{\mathrm{spread}}$ should not exceed 25 ns, which is approximately twice the time for electromagnetic wave propagation from the first cavity to the last cavity in vacuum. In addition, the rise time and FWHM duration of output voltages varying with ${t}_{\mathrm{spread}}$ are given. The results indicate that the rise time changes little at the beginning but increases exponentially once the ${t}_{\mathrm{spread}}$ exceeds 30 ns. The FWHM duration nearly increases linearly with ${t}_{\mathrm{spread}}$.

Electrical explosion of wires (EEW) driven by pulse current can produce plasmas with high energy density, and is accompanied by electromagnetic pulses, strong shock waves, etc., therefore it is widely adopted in Z-pinch, electrothermal chemical weapons, oil and gas exploitation and other fields. Compared to pure metal, alloy has characteristics of the high resistivity, adjustable composition, and complex phase transitions. It has great potential in regulating parameters of EEW. This paper presents an experimental study on exploding Cu, Ni, and Cu-Ni alloy (constantan) wires in atmospheric air under a microsecond time-scale pulsed current. Through the diagnoses of electrical parameters and self-emission images, the discharge characteristics and spatial-temporal evolution of explosion products were obtained. Features of the alloy wire explosion in phase transition and plasma were acquired as well. Experiments revealed that in the early stage of EEW, the high resistivity of the alloy could improve the energy deposition efficiency, namely 52% for Cu, 74% for Ni, and 78% for Cu-Ni, while after the explosion, performance of the alloy wire was closer to that of the Ni wire. The initial expansion rate of the plasma channel reached 5 mm/μs level but then decayed. The expansion process of alloy wire endured longer, and the average resistivity went up slowly after the breakdown. Also, a correlation was found between plasma radiation and metal aerosol in spatial scale. Especially, the alloy aerosol has crossed striation features (10−1 mm), but it is more uniform than Cu aerosol generally.

快脉冲测量探头是大型脉冲功率装置安全稳定运行的基石,研究其标定技术对获取准确可靠的脉冲功率装置运行参数具有重要意义。为此通过分析不同快脉冲测量探头的实际应用环境,利用同轴线脉冲方波成形原理,提出了快脉冲测量探头的2种规范化标定方法:在线标定和离线标定,其中,在线标定方法适合于受分布参数影响较大的测量探头,如微分环和电容分压器等,而离线标定方法适合于受分布参数影响较小的测量探头,如Rogowski线圈和小电阻分流器等。2种标定方法均获得了响应时间为ns量级的矩形方波脉冲,且具有相同的放电回路和具有可溯源到国家标准的测量不确定度,分析了测量确定不确定度的合成方法。研究结果将对快脉冲测量探头的规范化标定具有重要参考价值。

The discharge channel development of microsecond electrical exploding tungsten in air was investigated. A microsecond pulsed current source was used to trigger the electrical explosion of tungsten wires with a length of 40 cm and a diameter of 0.3 mm. Charged with a 26 kV voltage, a 6 μF capacitor possessed a stored energy of 2028 J, which was not enough to vaporize the tungsten wire. We proposed two parameters, the total cross-sectional area and the granular border area, to quantitatively describe the discharge channel development. We also adopted an image processing method to study the entire discharge channel development throughout the wire explosion. Evident results suggested that the trend of the electrical explosion was layer by layer from the surface to the core, and the outward expanding speed of the channel was gradually decreasing. The results also demonstrated clear distinction between the discharge channel developments at upper and lower electrodes. During the electrical explosion, the granular border area increased in an approximate exponential way, while the total cross-sectional area increased linearly until 1.43 ms and then decreased, which was caused by hollow regions formed in the discharge channel.

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.

在高压放电装置以及脉冲气体激光器领域中,电极面型所决定的极间电场直接影响装置性能.选取球头、平球头、Chang、Bruce四种面型的电极,使用有限元分析法对四种面型电极电场在三维空间内进行数值计算,找出各个电极二维截面电场强度最大偏差的位置,给修改造型提供依据.设置电极半径13mm,间距在7～10mm之间变化,分别构建四种电极曲面,设置两电极电势差为30kV,计算得到四种面型的d-f曲线,确定不同间距下最佳面型电极,对工程实践提供指导.在平球头与Bruce电极中心设置10μm半球凸起凹陷,测定烧蚀喷溅对于间隙电场畸变率的影响.

金属丝在快脉冲电流驱动下,受到欧姆焦耳加热作用发生电爆炸现象,并呈现出复杂的物理和化学效应,已广泛应用于工农业生产、新材料制备和核聚变等方面。文中综述了金属丝电爆炸现象的研究历史和应用情况,分析了金属丝在不同电流作用下的物理现象和规律,提出了一种金属丝电爆炸现象的分类方法,即以金属丝注入能量快慢的不同,将金属丝电爆炸现象分为欠热电爆炸和过热电爆炸现象,在过热电爆炸现象中,根据产生的电爆炸等离子体温度的不同,分为高温等离子体和低温等离子体,该类低温等离子体在不同的介质环境中具有不同的应用特点;分析了金属丝电爆炸现象的研究现状,即金属丝电爆炸等离子体的参数诊断方法以及相关数值模拟方法,讨论了金属丝电爆炸现象研究的难点、热点问题和下一步发展方向。

Based on high pulsed power technology, electrical explosion is increasingly utilized to generate shock waves with high pressure. To further magnify the shock wave pressure, we have proposed a novel technique by using energetic materials ignited by the plasma of microsecond wire explosion. Organic derivatives of nitramide, termed nitroamines, are widely used as powerful and relatively insensitive explosives. In this paper, we investigated the shockwave characteristics of nitramine (RDX and HMX) powders ignited by exploding copper wire (diameter 0.3 mm and length 60 mm). With charge voltage of 24 kV and powder mass about 6.0 g, the most evident experimental results suggested that the RDX load possessed higher peak pressure of 11.38 MPa and larger areal impulse of 503.02 MPa $\cdot \mu \text{s}$ , comparing with the shock wave of HMX load (7.22 MPa and 371.28 MPa $\cdot \mu \text{s}$ ). Moreover, the RDX load also had greater ascent rate of pressure, which was nearly twofold of that of the HMX load. Finally, a simple multi-factor ignition mechanism for nitramine powder under microsecond exploding wire plasma was proposed and discussed.

Based on high pulsed-power technology, electrical explosion is increasingly utilized to generate shock waves (SWs) with high pressure and short duration. To further magnify the SWs, we have proposed a novel technique by using energetic material (EM) loads. In this paper, we investigated the SW characteristics of ammonium nitrate (AN) powders ignited by the plasma of different kinds of refractory wire explosion. Evident results suggested that compared with $\Phi ~0.5$ -mm wires, $\Phi ~0.2$ -mm molybdenum and tantalum wires were able to finish vaporization, undergo the breakdown and eventually produce stronger SWs. After introducing the AN powders, the peak pressure of SW was scarcely enhanced, while the duration was significantly increased. Moreover, it was implied that various factors would affect the SW characteristics, including the EM charge density, the diameter, and material of metal wire. Finally, a simple plasma ignition mechanism based on multifactors was proposed.

To investigate the feasibility of applying the light-initiated explosive,silver acetylide-silver nitrate (SASN),as an effective simulation of a cold X-ray blow-off event,we carried out experimental researches on the detonation property of SASN ignited by a light flash.First we presented the basic and sensitivity character-istics of SASN,and then based on the analysis of its light-initiated mechanisms,we succeeded in igniting a large area of SASN sprayed layer by a light flash with high voltage,and conducted tests on the detonation characteristics of SASN sprayed layer initiated by light.The results indicate that SASN is a relatively safe agent of light-sensitive explosive with a relatively low detonation velocity of sprayed layer capable of providing low impulsive loads.The test results confirmed that the specific impulse of explosion from SASN is almost linear to the areal density of sprayed layer under the conditions of low-level density.