Hard-anodized aluminum has been demonstrated to improve the with stand voltage of vacuum gaps and is widely used in grading rings and flares of insulator stacks in pulsed power facilities. However, these coating films are prone to defects that can lead to failure. Understanding of the influence of coating parameters on pulsed vacuum breakdown characteristics has been limited. The effects of the thickness, porosity, and surface roughness of hard-anodized aluminum coating on a vacuum breakdown field are investigated in this study. Experiments were performed under a pulsed voltage with a full width at half maximum (FWHM) of 70 ns. The experimental results reveal that the breakdown field increases as the surface roughness of the coating decreases. As the coating thickness increases from 20 to 70 & micro;m, the breakdown field increases from 1040 +/- 362 to 1439 +/- 38 kV/cm. The results indicated that thicker films, shallower micrometer-scale pores, smoother surfaces, and reduced porosity are the key factors for enhancing the breakdown field in vacuum gaps. The findings of this study can enable practical engineering applications and improve the performance of pulsed power facilities.

The vacuum power flow section, which consists of insulator stacks and magnetically insulated transmission lines (MITLs), is a core component of the 4-MA linear transformer driver (LTD). Precise monitoring of vacuum power flow is essential for assessing the operational status and performance of the facility. The layout and design of the D-dot and B-dot probes are presented. A compact pulsed source, capable of generating voltage pulses with amplitudes of tens of kilovolts and current pulses with amplitudes of --- 10 kA, has been developed for probe calibration. The probes are in-situ calibrated level by level with the pulsed source positioned at the load region to ensure uniform current distribution and reliable calibration results. The sensitivity variations of the probes at different azimuthal positions are less than 5%. All the calibrated probes exhibit high consistency in measuring the vacuum power flow of the accelerator.

Load current multipliers (LCMs) were anticipated to enhance the energy and current coupling efficiency from the pulsed power drivers to low-impedance loads without significant modifications to pulsed power drivers. An LCM was designed and tested on a ten-stage linear transformer driver (LTD) module. The experimental results indicated that the short-circuit current of the LTD module was increased from 512 to 866 kA with the implementation of the LCM, indicating a current multiplication gain of 1.69, was obtained. The relationship of the LCM current multiplication coefficient depending on the load inductance, post-hole convolute parameters, and LTD output power was investigated, showing that the LCM current multiplication coefficient was dominated by the load inductance. When the LTD-LCM system was used to drive planar wire array loads, a current multiplication gain of 1.25 was achieved.

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.

Z-pinches can be used as a soft X-ray source to investigate the radiation coupling of planetary materials such as Fe and Al and the response of the sample to stress waves. In these experiments, the energy fluence on the sample must be measured, and a novel measurement presented in this article is just designed to determine the energy fluence incident on the target. The measurement system consists of a pinhole array and a nickel foil bolometer, while the pinhole array is used to attenuate the X-ray flux in an achromatic manner. Compared with the traditional means, this method is a direct measurement of the energy fluence, while the traditional way is deducing the fluence value based on the premise of an inverse-square radial dependence along a line-of-sight distance. Furthermore, this new method allows reduction of the X-ray intensity to avoid saturation problems while avoiding the spectral dependency of thin-film filters. This achromatically filtered bolometer has been installed on the Qiangguang-I facility to monitor the energy fluence on the target located 5 cm from the Z-pinch source, the diameters of samples are usually 1 cm or so, and the corresponding solid angles are 0.01 pi . The experimental results show that the pinhole array is feasible to be used as an attenuator. Furthermore, it can mitigate the nonuniformity of the radiation flux on the target when the Z-pinch X-ray source is distorted by magnetohydrodynamics (MHD) instability. The measured data on Qiangguang-I show that the energy fluence incident on the test object obeys the inverse-square law when the distance is bigger than 5 cm.

Flash x-ray radiography is an important diagnostic in hydrodynamic experiments to provide fluoroscopic imaging of fast-moving dense targets. In order to obtain multiple images of an object at different times in an experiment, a flash x-ray accelerator is required to output multiple pulses. For the induction voltage adder (IVA) multi-pulse accelerator, it is important to study the effect of the cathode plasma generated by the front pulse in magnetically insulated transmission lines (MITLs) on the transmission of the subsequent pulses. In this paper, a coaxial MITL experimental platform based on the "QiangGuang-I" accelerator is established to study the dissipation characteristics of the cathode plasma, and its working condition is similar to that of MITLs in typical IVA accelerators. In the experiment, a stable magnetic insulation is formed in the coaxial MITL, and the current loss along the line can be ignored. The microwave interferometer is used to measure the evolution of cathode plasma density over time for hundreds of microseconds after the pulse disappears. The measurement results of microwave interference show that the line-averaged density of the plasma in the anode-cathode gap is above 1 x 10(18) m(-3), and the time for the plasma density to decrease to 1 x 10(16) m(-3) is about 600 mu s. The expansion velocity of the plasma after a pulse is much lower than that during the pulse. In addition, the dissipation characteristics of the cathode plasma with different electrical parameters of the pulses are compared and analyzed.

A series of current transport experiments of a conical magnetically insulated transmission line (MITL) and a single post-hole convolute (PHC) had been done on a 12-stage linear transformer driver (LTD). The LTD produced a current with a rise time of about 120 ns and a peak varying from 0.5 to 0.8 MA depending on the terminated connection loads. The conical MITL was designed with a constant gap distance of 8 mm, which was equivalent to the MITL segments that are close to the PHC locations in the multi-level conical MITL in tens of megaampere current drivers. A single PHC was also designed to operate at conditions close to those fielded on tens of MA current drivers such as the Z machine. The experiment results indicated that there was almost no current loss along the constant-gap MITL before the peak current even the MITL figure of merit, i.e., E/cB varied from 0.1 to 1. However, the time when current trails appeared gradually advanced. The effects of the geometric sizes on the current transport efficiency of a single PHC were studied. It was indicated that the current transport efficiency of the single PHC was considerable high while the gap distance is larger than 6 mm. Whereas the PHC current loss was increased to about 30% when the gap is 3 mm. The dynamic impedance of the single PHC was obtained. During the pulse, as the plasma diffused, the convolute shunt impedance rapidly decreased, which was consistent with the known mechanism.

For a hybrid X-pinch load assembled in parallel with the return-current rods, the impedance of the hybrid X-pinch load is important for current division between the load and the current rods. In this paper, the experimental results of the investigation of the impedance of a hybrid X-pinch load on the Qiangguang facility (1.5 MA, 100 ns) were reported. The current of the X-pinch load was measured using a serial nickel foil resistor, and the voltage was measured using a two-stage resistive divider. The inductance of the X-pinch load was obtained by comparing the differential signal of the current with the voltage waveform, and it is about 4.7 nH, which is nearly equal to the calculated total inductance of the metal wire and the two X-pinch electrodes. The resistance of the X-pinch was determined by subtracting a part of the inductance from the measured voltage, and the following results were obtained. At the start of the current, the resistance of the X-pinch increases quickly from the metallic resistance of 0.16 Ω at room temperature for a 2-mm-length 30-μm-diameter Mo wire to 0.8 Ω in about 10 ns, and then, it falls fast to nearly zero, which suggests that the electrically exploding phase of the metal wire ends and the high conductive plasma is formed. As the current continues to flow through the Mo wire, the resistance increases once again from nearly zero to about 0.4 Ω at the moment when the X-pinch begins to burst x-ray radiation, which reflected that the micro-pinch dynamical process occurs and a hot and tight plasma zone is formed. Assuming that the tight plasma zone is 300 μm long with a 10 µm diameter and the temperature of the plasma is ∼1 keV, we can obtain that the resistance of the tight X-pinch spot is about 0.6 Ω, which is close to the value of 0.4 Ω obtained in the experiments.

Wire arrays are the typical loads which have been widely used in z-pinch research studies. When a large pulsed power accelerator is designed, the electrical parameters of the z-pinch loads including the inductance and the resistance (or the equivalent resistance) must be considered. In this paper, the inductance and the resistance of the single planar wire arrays were introduced from the experiments carried out on a Qiangguang accelerator (1.5 MA, 100 ns). The lumped-element circuit model of the wire array was established using the PSPICE software, and the model was verified by comparing the simulation results with the experimental results. The influence of the electrical parameters on the accelerator’s driving current is investigated. It shows that the inductance affects the rising edge and the peak value of the current, while the resistance mainly affects the current waveform after the stagnation of the wire array pinch load. The inductance model based on the zero-dimensional equation is compared with the inductance model based on the experimental data, and the result shows that the two different inductance models give almost the same pinch current. It can be concluded that the zero-dimensional model is valid in circuit simulation to investigate the peak current of the designed z-pinch accelerator.

The Z-pinch plasma radiation sources have recently provided the most powerful and energetic laboratory sources of multi-keV photons. The X-ray produced by Z-pinch plasma can be used to study the thermodynamic effect and the system-generated electromagnetic pulse effect, and to study the physical processes such as the conversion of X-ray deposition energy into internal energy and kinetic energy in the material. The impulse coupling mechanism and coupling coefficient of X-ray in different structure composites were obtained, the electromagnetic pulse effect of electronic components was studied experimentally, and the physical problems such as the non-linear interaction between strong pulse electron and electromagnetic field caused by X-ray photoelectric effect and Compton effect were analyzed. The parameters of X-ray for the study of thermodynamic effect of materials and electromagnetic pulse effect of electronic component system are presented, and the typical results of the study of radiation effect using Z-pinch plasma X-ray are introduced. The average energy produced by Z-pinch plasma is 0.21 keV, the average half-width is 36 ns and the average energy flux is 143 J cm(-2) on Qiangguang I accelerator. The measured coupling coefficient of injection impulse is 0.70 Pa s J(-1) cm(2). When the energy distribution of X-ray is 0.1-1.2 keV, the pulse width is 34-63 ns and the energy flux is 48-156 J cm(-2), the impulse coupling coefficient is 0.44-0.76 Pa s J(-1) cm(2) in Al material. The parameters such as energy spectrum, yield, irradiated area and uniformity of X-ray produced by Z-pinch load of different materials and structures driven by 30 MA current are given. The total output of characteristic X-ray of similar to 3 keV is about 607 kJ with an average energy fluence of 103 J cm(-2) at 20 cm and an irradiation area of 300 cm(2), the uniformity of energy fluence is 90%. In order to obtain harder X-ray, Mo, Ag, In, Sn, W wire array loads can be used to generate similar to 17, 22, 24, 25, 59.3 keV X-ray using non-thermal X-ray emission mechanism. In order to improve the efficiency of X-ray radiation of Z-pinch plasma, increase the yield of X-ray, some scientific questions that need further study have been put forward. In order to improve the efficiency of power coupling to load, it is necessary to study the mechanism of energy conversion from electromagnetic field to internal explosion kinetic energy in Z-pinch plasma. The causes of the instability of magnetic fluid dynamics and the theory of reducing the instability in internal explosion plasma should be analyzed. In order to improve the stability of Z-pinch plasma, it is important to study the interaction mechanism between thin shell-layer implosion plasma and magnetic field permeating into the wire array, and the influence of thermal spot and mass tugging in the process of implosion. The dynamics of implosion and axial inhomogeneity of radiation output, and the formation mechanism of "zippered" phenomenon and "snow harrow" stability should be studied. The energy conversion mechanism of Z-pinch plasma and the radiation mechanism of producing X-ray should be studied. In order to obtain harder X-rays, high Z atoms are stripped to H-like, He-like states, requiring higher voltages and higher currents to be fed into the load. The theory of producing K-shell X-ray by non-thermal excitation should be explored. In order to obtain more hot electrons, the technique of cathode slot, twisted wire array, plasma circuit breaker mechanism and local non-uniform magnetic field should be explored. The theory of increasing the ratio of K-shell radiation to low energy radiation should be studied by using the theory of local high temperature zone and microdiode. The technique for obtaining hard X-ray from the composite radiation of Z-pinch plasma should be studied.

基于快直线脉冲变压器（FLTD）平台开展了数十kA电流下Al单丝芯晕演化特性研究,实验发现丝过早发生电压击穿会减少丝芯的能量沉积,而晕等离子体的迅速发展将约束丝芯的进一步膨胀,降低丝芯膨胀速度。通过调整负载两端的初始电压、丝长及增加闪络开关等手段,抑制了Al丝的过早击穿,增加了早期能量沉积,获得了不同的丝芯物理状态（部分气化或完全气化）。Al丝的气化提高了丝芯膨胀速度,最高达11～14 km/s,晕等离子体发展缓慢,延缓了边界处不稳定性的出现,降低了后期m=0的发展速度。FLTD负极性输出时,Al丝沿轴向的极性效应更加明显,靠近阴极处丝芯膨胀慢,边界处晕等离子体密度高,不稳定性的发展速度快。

为了抑制丝阵Z箍缩中金属丝在电流早期电爆炸形成的芯晕结构,基于强光一号加速器,利用二级丝阵负载开展了Al丝阵早期物理状态的调控研究.通过陡化预脉冲和调整二级丝阵的参数,实现了负载Al丝的全部汽化,抑制了芯晕结构的产生,气态Al丝芯的平均直径约为1.80 mm,且沿轴向均匀分布,降低了丝阵消融引起的初始不稳定性.若丝长度和直径保持不变,反转型丝阵的关断时间主要取决于Al丝的丝数;反转型丝阵关断后,气态丝芯在主电流脉冲作用下迅速电离并开始内爆,磁瑞丽泰勒不稳定性迅速发展,内爆等离子体流沿轴向呈周期性调制分布,调制波长约为650μm.Al丝阵初始状态的改变,有效抑制了丝的消融过程,消除了先驱等离子体,在内爆后期降低了拖尾质量,提高了箍缩品质.

Z-pinch using a deuterium gas-puff load has been validated as a plasma neutron source on many accelerators such as Saturn, Z, Angara-5, and S-300. The experimental results on these accelerators show that the production of the neutron can be scaled as Yn∝Im4, where Yn is the yield and Im is the peak current of the accelerator, no matter what mechanism is eventually determined to be responsible for generating fusion neutrons. The neutron production on the Qiang-Guang I generator (1.5 MA, 100 ns) is analytically estimated that approximately 4 × 1010 D-D neutrons would be produced, among which the thermonuclear neutrons is only 7 × 107. The gas puff construction used on Qiang-Guang I is introduced, and the optimum line mass of the D2 gas is given. The results show that the optimum line mass is approximately 50 µg/cm for the driving current of Qiang-Guang I. The mass density distribution obtained with the classical ballistic-transport model demonstrates that the gas puff forms a hollow gas shell with the length of 2 cm. For D2 to produce a gas flow with the line mass of 50 µg/cm, the firing time of Qiang-Guang I changes to 250 µs and the absolute pressure of the chamber is increased to 4.2 atm.

In order to suppress the core-corona structure (namely, the dense wire core in atomic state surrounded by plasma with high temperature and low density), two-stage wire array experiments have been carried out on Qiangguang-1 generator (1.3 MA and similar to 80 ns). The results showed that the shutdown time of inverse array, which consists of a central cathode rod surrounded by wires, depended on wire number. The shutdown time was 40 ns after the start of main current, when two aluminum wires were placed in inverse array, which ensured that there was still enough time during main current for load array to implode and radiate X-rays. The vaporized wire cores expanded uniformly along the axis with a smooth boundary and the average wire diameter was 1.8-1.9 mm. The vaporized wire cores were ionized rapidly after the shutdown of inverse array. The perturbations of plasma instability were first observed at the boundary of vaporized core and developed rapidly after the start of implosion. The average wavelength of these perturbations was 600-650 mu m. The precursor plasma was barely observed on the array axis in optic images. The X-ray pulse output by vaporized wire array with mega-ampere current was first given. Considering the waveform of X-rays and main current, the pinch process of the vaporized load array tended to the quasi-shell implosion. Nevertheless, there were still some fractions of plasma being left down at the initial position to lead the second implosion for the rapid development of magneto-Rayleigh-Taylor instability in implosion, which resulted in the double peaks of X-rays. The suppression methods of the implosion instability will be further studied and explored in future.

为更深层次理解Z箍缩基本物理过程,认识单丝早期演化对丝阵后续内爆过程产生的影响,基于百千安直线脉冲变压器(FLTD)平台开展了不同材料(钨丝、镀膜钨丝和铝丝)单丝Z箍缩实验研究,实验获得了单丝演化过程的双分幅激光阴影和干涉图像.实验发现:初始直径相同(15 μm)的条件下,铝丝核的膨胀速度比钨丝核的快,在电流开始一段时间内,铝丝核沿轴向呈均匀膨胀,而钨丝核因电极效应沿轴向膨胀不均;镀膜钨丝(15 μm W+2 μm Polyimide)核的膨胀速度远大于钨丝核的,甚至高于铝丝核的,同时镀膜还降低了消融等离子体不稳定性的发展速度.

针对“强光一号”加速器Z箍缩负载产生的总能量约40 kJ软X射线功率密度测量问题,提出了利用针孔阵列对距离负载中心较近处试验面的功率密度进行衰减的物理方案,分析了针孔成像原理,设计了针孔阵列,计算了阵列衰减因数.分析计算结果表明,设计的针孔阵列可有效对软X射线功率密度进行衰减,衰减因数为4×10-6.同时,该针孔阵列可对由磁流体力学不稳定性引起的Z箍缩软X射线辐射源成像光强不均匀现象起到匀化作用,从而使利用该针孔阵列对试验面功率密度进行测量具备了可行性.

Experiments about single wire exploding were carried out on the fast linear transformer driver(FLTD),which pro-vides a current of about 100 ns rising time and about 100 kA maximum amplitude.Laser probe and visible framing camera have been set up for plasma diagnostics.In addition,visible detector PIN and XRD were used to measure the characteristic of radiation for single wire exploding.A series of images for single tungsten wire(1 5 μm W)and coated tungsten wire (1 5 μm W+2 μm Poly-imide)exploding experiments have been obtained,which show the evolution of wire ablating and the instability development of ab-lated plasma.The results show that wire coating will add more energy to the wire at the initial phase,hence improve the charac-teristics of wire exploding .

The design of high-current density magnetically insulated transmission line (MITL) is a difficult problem of current large-scale Z-pinch device. In particular, a thorough understanding of the MITL electrode surface evolution process under high current density is lacking. On the "QiangGuang-I" accelerator, the load area possesses a low inductance short-circuit structure with a diameter of 2.85 mm at the cathode, and three reflux columns with a diameter of 3 mm and uniformly distributed circumference at the anode. The length of the high density MITL area is 20 mm. A laser interferometer is used to assess and analyze the state of the MITL cathode and anode gap, and their evolution process under high current density. Experimental results indicate that evident current loss is not observed in the current density area at pulse leading edge, and peak when the surface current density reaches MA/cm. Analysis on electrode surface working conditions indicates that when the current leading edge is at 71.5% of the peak, the total evaporation of MITL cathode structure can be realized by energy deposition caused by ohmic heating. The electrode state changes, and diffusion conditions are reflected in the laser interferometer image. The MITL cathode area mainly exists in metal vapor form. The metal vapor density in the cathode central region is higher than the upper limit of laser penetration density (similar to 4 x 10(21)/cm(3)), with an expansion velocity of similar to 0.96 km/s. The metal vapor density in the electrode outer area may lead to evident distortion of fringes, and its expansion velocity is faster than that in the center area (1.53 km/s). (C) 2016 AIP Publishing LLC.

A kind of fast shutter for protecting the diagnosis devices in Z pinch experiments is introduced in this paper. The shutter is composed of a pulling rod, a magnetic core, and a solenoid. Different from the traditional coils which were used at the voltage of 220 V, the solenoid we used must endure the high voltage of 5-10 kV and the deformation which maybe caused by the 5-10 T intense magnetic field. A creative configuration for the solenoid is developed including the winding guide, insulating sleeve, and stainless-steel sleeve. The experimental results show that the configuration of the solenoid is effective. The velocity of the valve is nearly 19 m/s and the time jitter of the shutdown is within 75 μs.

The experimental results of the insulated-standard hybrid wire array Z pinches carried out on “QiangGuang-I” facility at Northwest Institute of Nuclear Technology were presented and discussed. The surface insulating can impose a significant influence on the dynamics and radiation characteristics of the hybrid wire array Z pinches, especially on the early stage (t/timp < 0.6). The expansion of insulated wires at the ablation stage is suppressed, while the streams stripped from the insulated wires move faster than that from the standard wires. The foot radiation of X-ray is enhanced by increment of the number of insulated wires, 19.6 GW, 33.6 GW, and 68.6 GW for shots 14037S, 14028H, and 14039I, respectively. The surface insulation also introduces nonhomogeneity along the single wire—the streams move much faster near the electrodes. The colliding boundary of the hybrid wire array Z pinches is bias to the insulated side approximately 0.6 mm.