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As an emerging kinetic damage weapon system, railgun has attracted much attention due to its remarkable advantages such as high initial speed, high kinetic energy, high shooting speed, high emission density, low cost, and antijamming. However, there are currently degradations of electromagnetic railgun launch performance and reliability, the limited service life as well, resulting from rail damage such as the transition erosion and grooving damage. Based on 24 consecutive shots, this paper presents the statistical analysis of B-dot probe data, aiming to show the working stability and reliability of the electromagnetic rail launch system when consecutive firing. On the basis of current data and B-dot probe data, the speed–displacement curve was obtained by simulation, through which it is easy to get the movement state of the armature in the launch track. Finally, by checking the disassembly of the launch rail, this paper analyses the damage states of launching rail after the 24 consecutive launch experiments. Through the above three aspects of research and analysis, this paper could be the reference for the further research and analysis on the performance and lifetime of railgun. [ABSTRACT FROM AUTHOR]

Self-integrating Rogowski coil has been widely used for measurements of pulsed currents from nanosecond timescale to microsecond timescale in pulsed power systems. Appropriate designs of coil’s structure are vital to high-frequency response. This paper proposed a new structure of Rogowski coil so as to provide a better response to fast pulsed current. Four Rogowski coils with different structures were tested in three different platforms. Experimental results showed that the hybrid Printed Circuit Board Rogowski coil had the best performance in this paper, which could respond to square waves with fronts of $\sim 2$ ns and had a sensitivity of 0.585 V/kA. The designed maximal peak current was 100 kA. [ABSTRACT FROM PUBLISHER]

This paper describes the design strategy for a new Marx generator, based on SiC metal–oxide–semiconductor field-effect transistors (MOSFETs), proposed for Kicker magnet applications. As a starting point, the possible replacement of a thyratron tube associated with an existing kicker system, at CERN, is considered. The specifications of the output pulse are: 40-kV, 3.2-kA, 3- $\mu \text{s}$ flat top duration, 30-ns rise- and fall-time, and 1-Hz repetition rate. A theoretical study for a Marx generator topology, using 50 stages, each 800-V stage comprising 24 SiC MOSFETs in parallel, each MOSFET conducting approximately 140-A pulses is considered. In addition, a four-stage prototype has been evaluated, with almost full current and 3 kV, based on the proposed design, in order to assess the technological advantages of such a system and limitations for the scale up. First tests using parallel SiC MOSFETs are described and results discussed in light of the proposed topology and the physical structure of the assembly. [ABSTRACT FROM AUTHOR]

In this paper, we report on the propagation behavior of the atmospheric-pressure and brush-shaped He/O2 plasma plumes generated by a specially designed plasma device. The measurements show that the frequency of applied voltage $(f)$ and the O2 fraction and flow rate of the feed gas significantly affect the discharge propagation of the atmospheric-pressure plasma plume in ambient air. The uniformity of the brush-shaped plasma plume is greatly improved at a relatively high $f$ or He/O2 flow rate. Addition of a trace amount of O2 into the He gas can also contribute to the formation of uniform and brush-shaped plasma plumes in ambient air. This paper confirms that the plasma device composed of well-aligned and micrometer-thick fibers can be utilized to generate large-scale plasma plumes for potential applications. The propagation of the He/O2 plasma plume in ambient air results from the applied electric field across the small gas spacing of a barrier discharge electrode configuration, where the He atoms are easily ionized or excited for generating the brush-shaped plasma. [ABSTRACT FROM PUBLISHER]

The results of an experimental study of the generation of runaway electrons (REs) during the formation of a negative streamer in an 8.5-mm-long point-to-plane gap filled with air are presented. Negative nanosecond voltage pulses (18 kV, $\tau _{0.5}\approx 10$ ns, and $\tau _{0.2-0.9} \approx 4$ ns) were applied across the gap. In this paper, we attempted to determine when REs are generated relative to the appearance of the streamer. In our previous studies of a positive streamer, we have shown that the formation of the streamer is accompanied by a dynamic displacement current (DDC) caused by the redistribution of electric field strength in the gap. This current can be easily measured with a collector placed behind a grounded grid electrode. The collector is typically used to measure the current of REs at negative polarity. In this paper, we were able to measure together and separately the DDC caused by a negative streamer and the RE beam current. This allowed us to accurately determine the moment of generation of REs. [ABSTRACT FROM AUTHOR]

Electron-caused electromagnetic pulse (ECEMP) is susceptible to occur into constitutive dielectrics of satellites during their mission due to natural space ionizing environment. This paper reports the numerical and experimental characterizations of the electromagnetic fields subsequently generated by the electrostatic discharges (ESDs) from the analysis of the resonant cavity modes and the replacement currents. ESDs are produced when the polytetrafluoroethylene (PTFE or Teflon) samples are irradiated by a 6-MeV electron beam generated by the linear accelerator (LINAC) facility. The measured electromagnetic fields and currents are reproduced by a parametric analysis based on the 3-D Maxwell solution. Such a reproduction of the measured currents and magnetic fields allowed us to quantify the temporal and spectral characteristics of the ESD. It is shown that ESD is produced by bulk currents in the dielectric composed by a fast contribution (rise time lower than 100 ps) and a slower one (of about 200-ns duration). [ABSTRACT FROM AUTHOR]

In this paper, launch experiments are performed to investigate the effect of current and speed on current melt erosion with a 20-mm caliber lab-scale railgun. Armatures are kept in bore by using payload separated method to keep recovered armatures intact. Launch experiments with different current magnitudes are conducted, while speed is limited within 150 m/s by heavy payloads. Launch experiments are conducted at different speeds at the same current magnitude. The desired speed was achieved by adjusting the mass of payload for each test. Erosion results with increasing current and speed are summarized. Location of peak erosion depth and erosion amounts under the effect of current and speed are analyzed based on current simulation and profile measurement. The current melt erosion starts at the side edge near the midpoint of the armature in the longitudinal axis direction. Then, this erosion spreads longitudinally forward to the leading edge along the sides and transversely to midline of armature surface under the influence of current but moves toward to trailing edge under the influence of speed. Higher current and speed will facilitate the corresponding erosion propagation. The location of the peak erosion depth appears to be stable in space for the increasing current magnitude, which is consistent with stationary current simulation at upslope current stage, but gradually moves toward to the trailing edge as speed increases. This may because location of peak current density moves toward to the trailing edge due to the velocity skin effect. Measurement results of mass loss indicate that the amount of material eroded increases substantially with current, and less so with speed. Furthermore, the propagation trend of current melt erosion is discussed. [ABSTRACT FROM AUTHOR]

The rail life is an important factor that influences the rail-type electromagnetic launch (EML) engineering. This paper gives an introduction about the structure of the rail-type EML system, makes an analysis of some indirect or direct factors that affect the rail life, and points out the sectional characteristics of the rail life. By optimizing the armature-rail structural design and material matching and taking measures to control the discharge waveform of pulse current, it is possible to prevent the rail surface from being damaged. However, the mechanical fatigue caused by multiple launches and the plastic deformation under thermal stress will result in a decrease in performance of the rail. [ABSTRACT FROM AUTHOR]

When the pressure and temperature of a fluid exceed a critical point, the fluid enters into the supercritical (SC) region. In this region, the physical properties are believed to be in favor of a good current interruption medium. This paper focuses on the arc voltage characteristics of nitrogen arcs burning inside cylindrical tubes at different filling pressures: 1, 20, 40, and 80 bar, thus covering the SC region. Two different tube materials have been used in the experiments, alumina and polytetrafluoroethylene. Arc voltages are measured for arcs burning inside tubes of 2, 4, 8, and 15 mm inner diameters. In addition, free-burning arcs have been investigated at the same filling pressures. The arc current was 150 A at 350 Hz throughout the study. The arc voltage is found to increase with decreasing inner diameter of the tube at atmospheric pressure. At higher filling pressures (i.e., 20, 40, and 80 bar), however, such a simple relationship is not observed. The arc temperature and radius have been calculated based on the “simple theory of free-burning arcs” and the “two-zone ablation arc model.” The calculated arc radius decreases with increasing gas pressure. Furthermore, due to increased absorption of radiation at high filling pressures, ablation is found less significant for ultrahigh-pressure nitrogen arcs compared to atmospheric pressure arcs. This is in line with the observations from optical micrographs of the inner surfaces of the tubes exposed to arcs at different filling pressures. [ABSTRACT FROM AUTHOR]

Pulsed microdischarges produced by dielectric barrier discharges (DBDs) in a submillimeter gap were investigated under 200 cycles of sinusoidal ac voltage at 5 kHz in this paper. The impulsive current in the external circuit was accurately measured by an oscilloscope with a bandwidth of 2.5 GHz and a maximum sampling rate of 40 GS/s to calculate the filamentary current in the discharge gap. The amplitude, pulse duration, and transferred charge of a single filamentary current and the microdischarge energy acquired over the 200 voltage cycles were statistically analyzed for different discharge gaps and gas pressures. The microdischarge parameters and ozone generation efficiencies for different conditions were compared. The ozone production efficiency was found to increase with increasing pressure from 1 to 2 bar absolute, and the gap length from 0.2 to 0.5 mm. The maximum ozone production efficiency achieved in the paper was 217 g/kWh, with a gap length of 0.5 mm, an absolute pressure of 2.0 bar, and an applied voltage of 5.5 kV at 5 kHz. [ABSTRACT FROM AUTHOR]

The objective of this paper is to determine the influences of the transverse magnetic field (TMF) and the axial magnetic field (AMF) on prestrike inrush current arc behaviors in vacuum interrupters (VIs) during capacitive making processes. Two types of cup-type VI contacts were used: TMF contacts and AMF contacts. The contact diameter of the VIs was 48 mm. The insulating envelopes of the VIs were transparent, and there was no metal vapor shield inside the VIs, which were arranged for the observation of the prestrike arcs. The inrush current arc behaviors were recorded by a high-speed charge-coupled device video camera. The experimental results revealed that the VIs of cup-type AMF contact showed a higher dielectric strength than those of cup-type TMF contact during the making operations of inrush current. In addition, the arcs in VIs of cup-type TMF contact tended to be intense arcs that caused serious welding than those of VIs of cup-type AMF contact. Moreover, the cup-type AMF contact effectively reduced the prestrike arc erosion on the contact surfaces than those of TMF contact during the prestrike process of inrush current. [ABSTRACT FROM AUTHOR]

Tokamak devices such as ITER, EAST, and HL-2M have been designed and constructed (or under construction) to challenge the magnetic-confined nuclear fusion technology for the sustainable energy problem of human beings. The magnet system of the tokamak devices is mainly composed with poloidal field (PF) coils, toroidal field (TF) coils, and central solenoid coils. Among them, the PF coils play a key role in adjusting the confining magnetic field for the control of the fusion plasma. In order to avoid the plasma disruption, it is necessary to know the correlation of the magnetic field in a vacuum vessel (VV) with the current in PF coils and to predict the current distribution of PF coils which can generate a required configuration of confining magnetic field. In this paper, taking the HL-2M tokamak device as an example, an inverse analysis scheme to predict and identify the perturbation of current in PF coils from the target magnetic field signals in the VV was proposed. First, based on the Biot–Savart law, a forward code to calculate the magnetic field due to PF coil currents and TF coil currents was developed. Second, an inversion code to predict and identify current distribution in PF coils from the target magnetic field was developed based on the conjugate gradient optimization method and the singular value decomposition method. The validity of the proposed inversion scheme and the corresponding numerical codes was investigated by reconstructing PF coil current distributions from several groups of perturbed magnetic fields. In addition, the effect of the measurement points and the measurement noises on the reconstruction results was also discussed. Finally, a simplified experiment on a coil system was conducted to verify the validity and efficiency of the proposed forward and inversion analysis code. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose a new method to quantitatively determine the arcing rotation characteristics of the constricted vacuum arc driven by the transverse magnetic field (TMF). This method is based on a split-anode TMF contacts’ system, including a split-anode TMF and a spiral TMF cathode. Experiments were carried out in a demountable vacuum chamber. Both contacts had a diameter of 60 mm. The anode surface was divided into four areas: one central area and three symmetrically peripheral annular areas. The currents of the four split-anode areas were measured using four Rogowski coils situated outside the vacuum chamber. The observed arc behavior was recorded by a high-speed charge-coupled device video camera. This experiment proposes a new method to quantitatively determine the arcing rotation velocity of the TMF vacuum arcs by the current waveforms of the four split-anode areas. After some comparison to the new method, the rotation velocity of the TMF vacuum arcs estimated in the traditional method by the arc photographs seems underestimated. The experimental results indicate that the constricted vacuum arc driven by the TMF should be higher than 471 m/s with the arc current of 16-kA rms. The results also reveal the corresponding anode current distribution characteristics under the TMF in different arc stages during the arcing period. [ABSTRACT FROM AUTHOR]

In this paper, a new type of Rogowski digital integrator signal processing system has been developed for the dc test platform which located in the Institute of Plasma Physics. This signal processing system is mainly composed of the dual-coil subtraction structure and the digital signal filtering processing method that comb filter combined with high-pass filter (HPF) and low-pass filter (LPF). Trigger noise comes from the converter; it can be coupled to the integrator through distributive capacitance between dc bus bar and Rogowski coil; it will affect the integrator seriously; for example, the amplifier in integrator will be saturation, and the integrator cannot work, burrs lying in integration result. The dual-coil subtraction structure can attenuate the trigger noise significantly from hardware perspective and is convenient for the integrator to take a high gain without saturation. The comb filter combined with HPF and LPF can attenuate the trigger noise further and smooth the integration result. The experiment indicates that the approach proposed in this paper can reduce the impact of trigger noise on the integrator and improve the measurement accuracy. [ABSTRACT FROM AUTHOR]

The test about simple central difference average (CDA) + MIK ( $\text{M}_{ik}$ mutual inductance between ith and kth component) quench detection method implemented a total of about 100 charging runs on EAST in the past two years, aiming at verifying this new method whether to apply it to ITER CS coils or not. This project is supported by the ITER Organization. To obtain this target, the whole instrumentation hardware have been developed and installed on EAST and used to generate experimental data. Considering the whole new CS coils connection configuration and the possible risk for EAST device, the typical achievement is to accomplish successfully plasma scenarios (the longest shot of plasma current around 250 kA and pulse 3 s) by using a simple CDA + MIK quench detection method on EAST for the first time. Moreover, the numerical quench detection model has been designed, and the numerical signals are in good agreement with experimental data. Recent experimental results showed that CDA + MIK technology is applicable to the ITER CS coils as a backup method but the sensitivity of this system should be improved greatly in order to meet experiment requirements for ITER operation in the future. This paper introduces the test program, typical achieved operation, and the results of preliminary analysis. [ABSTRACT FROM AUTHOR]

Secondary electron emission has an important role on the triggering of the multipactor effect; therefore, its study and characterization are essential in radio-frequency waveguide applications. In this paper, we propose a theoretical model, based on equivalent circuit models, to properly understand charging and discharging processes that occur in dielectric samples under electron irradiation for secondary electron emission characterization. Experimental results obtained for Pt, Si, GaS, and Teflon samples are presented to verify the accuracy of the proposed model. Good agreement between theory and experiments has been found. [ABSTRACT FROM AUTHOR]

In this paper, a compact circuit topology is presented for pulsed power generation with a semiconductor opening switch (SOS). Such circuits require the generation of a fast forward current through the diode, followed by a reverse current that activates the recovery process. In general, magnetic switches are used to switch the diode current from forward to reverse. Therefore, adjustment of the output voltage of an SOS pulser is difficult. This paper introduces a circuit that allows an adjustable output voltage of the pulser. A solution is realized with a premagnetizing circuit on the primary winding of a pulse transformer (PT), so that a third winding is not needed. The primary capacitor voltage can now be varied while maintaining proper saturation of the PT. [ABSTRACT FROM PUBLISHER]

Due to the impact of arcing on high-purity surfaces and bound residual gases, current interruption operations may influence the internal pressure in vacuum interrupters (VIs). In this paper, we investigate the temporal development of internal pressure in VIs immediately after a current interruption operation, both intrusively using a vacuum gauge and nonintrusively using the magnetron method. By means of an experimental test setup that consists of a vacuum test system to vary the internal pressure in punctured, nonvented VIs with active getter elements, we performed experimental test series under variation of internal pressure and arcing time. The experimental results indicate that arcing during the interruption operation predominantly causes a significant decrease in the internal pressure of up to several orders of magnitude, depending on the arcing time and the initial pressure before the current interruption operation. Based on a test series with passivated getter elements, we found that active getter elements have only a minor influence on the observed pressure decrease. With regard to a condition assessment of vacuum circuit breakers, we discuss the impact of the observed pressure reduction effect on the possibility of predicting the remaining service life of installed VIs. [ABSTRACT FROM PUBLISHER]

Measuring the armature speed in bore and the rail current is very important in doing a further research for the launcher design. The B-dot probe method we often used has limited number of probes and its mathematical fitting curve has no actual physical meanings. Therefore, the current waveform’s shape information was used to improve the B-dot probe method’s result. The combined method could give an armature’s velocity at an arbitrary position, and the current waveform could also be calculated out at the same time. Although the combined method was suitable for the measurement, the transient situation limited the accuracy of the results. According to the transient current, the inductance gradient and the distance between rails and a probe are changing during the launching process. In this paper, this two varied parameters that influence the combined method are discussed. The experimental data shows that the improvement of the combined method is more reliable and suitable. [ABSTRACT FROM PUBLISHER]

The dielectric recovery process is a crucial stage of current interruption in a vacuum circuit breaker (VCB). The postarc current is an important macroscopic electric characteristic of the dielectric recovery process, which has caused many concerns in the past few decades. In this paper, the postarc currents of VCBs with different types of contacts, such as butt contacts, axial magnetic field contacts, and transverse magnetic field contacts with different materials are measured with a high-resolution current-zero diagnostic system. Besides, the appearance of vacuum arcs is recorded using a high-speed camera in the experiments. The relationship between the arc memory effect and the postarc current is analyzed. What is more, the influence of the instability of the vacuum arc shape on the dispersion of postarc current is also studied. [ABSTRACT FROM AUTHOR]

A novel double-type contact system with still-spaced contacts was proposed to offer a better arc control and a electric field shielding effect to the eroded inner contacts, especially during the capacitive interrupting process. The experimental double-type contact system consisted of the inner moving transverse magnetic field (TMF) contacts and the outer still-spaced axial magnetic field (AMF) contacts, which was called as TMF–AMF contacts. The objective of this paper is to determine the transformation characteristics of high-current vacuum arcs with still-spaced contacts under TMF–AMF combined magnetic fields. The experimental investigation includes the vacuum arcing behaviors, the arc voltage, and the arc current transformation characteristics. The arc current in the tests varied over a range from 0 to 30 kA at 50 Hz. The contacts material was CuCr25 (25% Cr). A high-speed charge-coupled device video camera was used to record the vacuum arc appearance. The experiments indicate that the vacuum arc current can transform successfully from the inner TMF contacts to the outer still-spaced AMF contacts for the novel TMF–AMF double-type contacts. The partial arc current flowed through the outer still-spaced contacts was mainly at the latter half of the vacuum arc duration and less than 50% of the total arc current. The value and polarity of the arc current also play a significant role in the arc current transformation characteristics of the TMF–AMF contacts with still-spaced contacts. Moreover, with the vacuum arc expanding to the still-spaced contacts, the variation of the Lorentz force of the arc column would weaken the rotation of the arc column and strengthen the transformation characteristics of the vacuum arc column to the still-space AMF contacts significantly. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers are well established in the distribution levels of the electrical power grids. To maximize the short-circuit interruption performance, an radial magnetic field (RMF)-contact design forces the arc from a fault current to rotate. The performance of the RMF-contact designs is usually evaluated in a model vacuum chamber with viewing ports that allows observing arc rotation with the help of high-speed cameras. These setups differ significantly from lifetime sealed vacuum bottles in geometry (and thus volume) and due to the fact that the main metallic vapor shield cannot be present. This, in turn, can affect the arc rotation behavior. In order to overcome these shortcomings, a new diagnostic tool has been developed to analyze the arcing behavior in standard lifetime sealed vacuum interrupters. Optical methods are not possible here, since the view is blocked by the opaque ceramics and the metallic vapor shield. For this reason, a Hall-sensor-based measuring system is applied, in which the variation in the magnetic field from the arc position is observed by multiple sensors. This paper presents the comparison of arc motion in lifetime sealed vacuum interrupters with different bottle geometries. For this purpose, investigations with identical spiral-shaped RMF contacts inside different vacuum bottle designs with differing vacuum volumes are performed. Also, for comparison, an interrupter with contrate cup contacts was investigated. Similarities and differences between the corresponding arc motion behaviors are discussed. [ABSTRACT FROM AUTHOR]

Wireless intraspacecraft communication technology is being developed for signal transfer on space missions to save weight and simplify the design. One consideration for this new technology is its interaction with space environment-induced electrostatic discharges (ESDs). The short time scales of spacecraft ESD events result in broad frequency band signals that can interact with high-frequency wireless antennas. These interactions present a source of signal noise. However, they also present a possibility of in-flight wireless ESD monitoring. We present laboratory measurements of arcing on common spacecraft insulators using commercially available single-band 2.4-GHz and dual-band 2.4-/5.8-GHz Wi-Fi antennas. These wireless detections are shown to coincide with direct simultaneous measurements of discharge event currents. The amplitudes of the wireless signals are shown to provide a measure of the relative magnitude of the arcs, although the narrow frequency ranges of Wi-Fi antennas make absolute measures of the discharge intensity impractical. The wireless signals are shown to provide very accurate nanosecond timing of ESD events, which presents the potential of identifying arc location on a spacecraft with the use of time-of-flight detection from multiple antennas. [ABSTRACT FROM AUTHOR]

In this paper, we studied the process of vacuum surface flashover of several polymeric materials initiated by 80-kV, 15-ns pulses with peak discharge current 3 kA. We measured breakdown propagation speed, energy input to the discharge, full ion charge and directional pattern of the plasma flow, the full energy of the particle flow, propellant mass loss, and thrust for polytetrafluorethylene (PTFE), polyethylene (PE), and polymethyl metacrylate (PMMA). In the case of PTFE, we obtained the maximum absolute values of thrust ($4.7~\mu \text{N}\cdot \text{s}$) and the full energy (66 mJ). The values of average mass velocity for all materials lie in the range of 3–7 km/s; values of the average velocity of ions lie in the range of 60–85 km/s. Directional patterns of charge and mass are similar and have distinct symmetry in equatorial and meridional planes. We estimated the temperature of the dielectric surface within a model of energy transfer from the discharge channel to the surface due to thermal conductivity. We showed that at this power level ($\sim 10^{7}$ W) and short duration of high-current stage of the discharge ($\sim 10^{-8}$ s), the propellant is consumed mainly during the stage of plasma channel formation. [ABSTRACT FROM AUTHOR]

Field emission cathodes made from single bulk carbon nanotube (CNT) fibers have demonstrated high emission currents and long lifetimes. This paper investigates the goal of achieving even higher current levels from field emission array (FEA) cathodes comprised of multiple CNT fibers arranged in various array configurations. Arrays were fabricated with 25- $\mu \text{m}$ -diameter CNT fibers in 2-fiber ($1 \times 2$), 4-fiber ($2 \times 2$), and 25-fiber ($5 \times 5$) configurations, and their field emission properties were measured. The $1 \times 2$ and $2 \times 2$ FEA cathodes achieved the maximum current values that scaled to greater than 2 mA per emitter. The $5 \times 5$ FEA cathode achieved a high maximum current value of 22 mA and exhibited stable emission for 10 h at ~9 mA at an applied field strength of 0.11 V/ $\mu \text{m}$. The Fowler–Nordheim theory was used to calculate the effective field enhancement factor ($\beta _{\mathrm {eff}}$) values for all of the arrays. Electrostatic simulations were performed using COMSOL Multiphysics modeling software to model the field enhancement of a perfectly uniform $5 \times 5$ array. The $\beta _{\mathrm {eff}}$ value for the total array was compared to the individual $\beta $ values at the fiber tips predicted by a surface potential model that predicted the field amplification of all 25 CNT fibers in the array. [ABSTRACT FROM AUTHOR]

Measuring the solid armature’s in-bore motion state using B-dot probes is significant for studying the electromagnetic emission. The common method uses B-dot probes to acquire the discrete time points when the armature passes by them. These points can be interpolated into a curve of the armature’s displacement. However, considering the rapid current changes, the points contain an error. What is worse, it is difficult to recover the armature’s whole process motion by limited discrete points. In this paper, by deeply digging out the information contained in induced electromotive force curve of B-dot probes, a novel measurement method is proposed, which we can recover solid armature’s in-bore whole process motion without any interpolation. At the beginning, considering the current skin and velocity skin effects, a precise 3-D model is built. By analyzing the effect of the current changing rate, the discrete precise time points when the armature passes by them are getting. Then, through the mathematical transformation and applying Newton’s second law, a novel method to acquire velocity curve, displacement curve, and acceleration curve of armature’s in-bore motion in the whole launch process is put forward. Finally, the simulation model of 9-m rail gun with 18 B-dot probes is built. Simulation shows that the proposed method can obtain precise armature’s in-bore motion state in the whole electromagnetic emission process and can deduce in-bore force curve of the armature, which is significant for fault diagnosis of launcher. [ABSTRACT FROM AUTHOR]

The effects of the position of the current probe on electrical measurements as well as those of typical materials on the current of a He plasma jet during the interaction of the plasma jet with surface materials were investigated using a dielectric barrier discharge reactor, in which the two electrodes were isolated from ambient air by electrical insulating oil. Here, we demonstrate accurate discharge power measurement obtained by positioning the current probe between the two electrodes rather than on the ground wire. The emission current of the plasma jet increased sharply upon the interaction with a ground-connected metal surface, because in this case, the surface functioned as a second ground electrode. Similarly, important is that the average velocity of a plasma bullet can be estimated from the phase shift of the current waveforms at different positions. The phase shift can be monitored by an oscilloscope using a cursor tool during the plasma discharge process. The average velocity of the plasma bullets in this paper ranged from 56 to 266 km/s. [ABSTRACT FROM AUTHOR]

This paper shows the correlation of the characteristic Ne soft X-ray (SXR) signal pulse with computed dynamics of the plasma focus using doped neon in Ne (97.5%)/Kr (2.5%) admixtures. The Lee model code is coupled with a specifically designed correlation excel template. The results show that typically, the characteristic Ne SXR pulse signal starts after the start of the reflected shock (RS) and before the beginning of the pinch. Specifically, in the illustrated shot, the RS phase starts at $3.375~\mu \text{s}$ while the pinch phase starts at $3.384~\mu \text{s}$. The characteristic Ne SXR signal pulse starts at $3.377~\mu \text{s}$ , which is 2 ns after the start of the RS and 7 ns before the pinch starts. There is a consistent trend of Ne SXR correlation with the computed dynamics in the Ne doped with Kr admixtures up to a doping level of 2.5%. [ABSTRACT FROM AUTHOR]

To realize the broadest potential of nonthermal atmospheric-pressure plasma (APP) technology, there is a need to develop low-cost, compact devices that can be used for portable applications. One of the greatest impediments to this is the power supplies and/or electronics needed to generate breakdown at atmospheric pressure. Piezoelectric transformers (PTs) are solid-state transformers that can produce large gains in voltage, which along with their modest size, makes them attractive candidates for use in plasma production. In this paper, we use a low-voltage power supply in line with a PT to produce an APP jet (APPJ). While operating at the resonance frequency of the PT (88 kHz), plasma jets were generated with input voltages as low as 10 V. The electrical and optical characteristics of the piezoelectric-driven jet were compared to an APPJ produced with a high-voltage sine wave of comparable operating frequency. Both APPJs were examined in helium and argon for a variety of different flow rates and operating voltages. In argon, the length of the jets was nearly identical for all operating parameters but produced different discharge currents. In helium, the discharge currents were similar but the lengths of the jet differed. Optical emission spectroscopy showed similar chemical composition between the two jets for both feed gases. Together, the results suggest that the piezoelectric material has an influence beyond simply amplifying voltage but can be successfully integrated to meet the requirements needed for plasma production. [ABSTRACT FROM AUTHOR]

In this paper, a high-dynamic and high-precise optical current measurement system based on the Faraday effect is presented. First, the sensor concept is presented and different sensor constructions are analyzed. Then, a measurement system based on a rare-earth iron garnet film is investigated. The measurement system uses multiple signal processing channels to increase the signal-to-noise ratio. Furthermore, the measurement range exceeds a rotation of 180° and therefore requires a counting mechanism to count the number of rotations. Finally, the precision of the presented system is analyzed. The precision is determined to be 4.9 ppm at a rotation range of 3300°. [ABSTRACT FROM PUBLISHER]

The unexpected arcs generated in a railgun bore are one of the major issues affecting emission efficiency. To study the impact of such arcs, a series of experiments with the same launch parameters has been conducted. B-dot probes positioned along the length of the launcher provide data for detecting arc formation phenomena and for measuring the armature velocity. In this paper, two sets of typical signals are discussed. The first set of signals is normal, whereas the other is abnormal in terms of the existence of an arc in the bore during launch. The time interval during which the arc generated and the state of the arc are determined from the magnetic induction curves by integrating the B-dot probe signals. Using a fitting analysis, the displacements and velocities of the armatures are obtained, and the energy distribution of each shot is computed. The results indicate that the generation of an arc in the bore causes a hash launch environment and greatly reduces the emission efficiency. [ABSTRACT FROM AUTHOR]

Chinese fusion engineering test reactor (CFETR) is under conceptual design to bridge gaps between ITER and DEMO. CFETR is envisioned to produce a 200 MW (200 MW in phase I and will be increased to 1-GW level) fusion power with tritium breeding ratio >1 and a duty cycle time of approximately 0.3–0.5. This paper is to present the status in the conceptual design of CFETR diagnostic system. Based on the experience obtained in the development of ITER diagnostics and combined with CFETR special requirements, progress of CFETR diagnostic system has been described. They mainly includes: 1) the conditions and constraints in CFETR environment and 2) one set of proposed measurements and candidate diagnostic techniques for CFETR phase I. The possible needed R&D activities for future work are under review. Two R&D examples under progress will be introduced. [ABSTRACT FROM AUTHOR]

This paper presents a work that was aimed to develop methods along with test facilities for characterizing the arc/contact movement in low-voltage miniature circuit breaker which has a related current under 125 A, and to find its relation with the short-circuit current/voltage in the circuit. The method consists of: 1) the high-speed camera for obtaining the image of the arc or contact movement; 2) the data acquisition system that measures the current during the short-circuit break; and 3) the circuitry system that establishes the synchronization of the arc movement capturing and the current acquisition. In particular, two methods were developed for this purpose: one based on analog signal and the other based on digital signal. The experiment shows that the accuracy of the synchronization, dependent on the sampling rate of the high-speed camera, is about from tens of microseconds to hundreds of microseconds with both methods. The two methods have their own advantages and disadvantages, and they can be tailored to applications for the best performance. [ABSTRACT FROM AUTHOR]

This paper focuses on the vacuum arc commutating characteristic (VACC) between the parallel-connected vacuum arc and the shunt resistor, which is the base of the postarc current (PAC) measure. The test platform is established in the synthetic test circuit. The influence of the current magnitude, shunt resistor, arcing time and current frequency on time of the current commutation and the current in the moment of the completion transition is investigated. The mathematic description of the VACC is obtained, which is useful to parameter design of the PAC measure. The PAC of 10-kV vacuum circuit breakers is measured in synthetic test circuit. The photos of the vacuum arc and the waveform of the current commutation are gained to verify the success of the commutation. In conclusion, the VACC is gained and applied to measure the PAC. [ABSTRACT FROM PUBLISHER]

In the case of back-to-back capacitor banks switching, the inrush current arcs can locally melt the contact surfaces of vacuum interrupters (VIs) during the prestrike process. The contact materials significantly influence the behaviours of the inrush current prestrike arcs. The objective of this paper is to determine the influence of contact materials on prestrike arc behaviours of VIs during capacitive making processes. Six identical 12-kV VIs were used in the experiment after the proposed conditioning. The contact diameter of the VIs was 48 mm, and the insulating envelope was transparent. There were no metal vapour shields inside the VIs to enable the observation of the prestrike arcs. Two different contact materials (CuCr50/50 and CuW10/90) were used in the experiment. Test inrush currents were set to 5-, 10-, and 20-kA peak values, respectively. The inrush current arc features were recorded by a high-speed charge-coupled device video camera. It is discovered that the contact materials have a significant influence on the prestrike gaps. Moreover, the prestrike arcs in VIs with the CuW10/90 contact material tend to be more diffuse than those in VIs with the CuCr50/50 contact material. The results indicate the impact of different contact materials on the prestrike arc behaviours and reveal the contact erosion patterns for different materials. [ABSTRACT FROM PUBLISHER]

This paper proposes an efficient modeling and an identification method for dielectric barrier discharge (DBD) systems, based on input–output (current–voltage) experimental measurements. The DBD is modeled using an equivalent electric circuit associated with a differential equation that describes the dynamics of its conductance. This equation assumes a homogeneous behavior of the gas. This paper introduces a series of polynomial terms of the current of the gas into the conductance equation. These terms, after identification, are a very useful tool to analyze the physical mechanisms that take place in the gas. The identification process also returns the numerical values of other DBD parameters, such as associated capacitances and the breakdown voltage. In addition, an asymmetric model for the gas, which considers the direction of the current, is proposed to consider the possible geometrical dissimilarity between the two electrodes of the DBD setup. Experimental measurements taken on two different DBD applications are used for validating the proposed approach. [ABSTRACT FROM PUBLISHER]

The demand for greater flexibility and increased energy density in pulsed-power systems is moving highly interactive components closer together. The development of compact technologies for less complex and more robust system designs is critical. A key system component that can impact these goals is the trigger generator (TG). Inexpensive, compact, and fiber-optically controlled TGs that deliver trigger pulses with subnanosecond jitter have been created with photoconductive semiconductor switches (PCSSs). However, high-voltage (HV) GaAs PCSSs are typically pulsed charged for less than 100 \mu\s so that they can hold off 60–100 kV/cm without self-triggering into high-gain (lock-on) switching or initiating surface flashover. Since many new pulsed-power system designs are based on dc-charged HV switches, pulse charging the trigger system is an additional complication requiring space, HV switching components, and HV cables. A further improvement in PCSS-based TG is to move from pulsed to dc-charged PCSSs. This paper reports results from dc-charged GaAs PCSSs with 0.25–1.0 cm gaps, extending previously reported results on smaller devices at 3 kV to a new regime of 100 kV. To hold off high fields for longer periods and to extend GaAs PCSSs to dc applications, we have utilized neutron-irradiated GaAs (n-GaAs). Neutron irradiation in GaAs increases the defect density, shortens the carrier recombination time, and (for devices with large insulating regions) reduces the dark current, which improves the dc hold-off strength. PCSS contacts in this research were created using rapid thermal annealing (RTA) to produce high adhesion and low contact resistance. However, this can reduce the defect density near the contacts by annealing some of the n-induced defects. Hence, a range of RTA temperatures and neutron doses was studied to understand the tradeoff space for contact adhesion and dc hold-off. This paper presents results from I–V characterization and dc hold-off on irradiated and nonirradiated GaAs PCSSs. These PCSS devices were demonstrated to hold off fields of 39–61 kVDC/cm, respectively. Irradiation doses over a range of \3 \times \10^13 - \1 \times \10^15 (1 MeV Si equivalent) were explored in search of the optimal performance. Additionally, the impact of the fabrication processes on the benefits of irradiation is explored, and the observation of unusual low-frequency oscillations during GaAs I–V testing is discussed. [ABSTRACT FROM PUBLISHER]

This paper investigates the influence of the axial magnetic field (AMF) arc control on voltage distribution (VD) of double-break vacuum circuit breakers (VCBs) in order to gain balanced VD, and thus enhance the breaking capacity. The interaction of vacuum arc plasma, postarc current (PAC), and AMF is discussed. We conduct the breaking test of double-break VCBs with externally applied AMF of a different pulsewidth, magnitude, and a different moment. The PAC, postarc charge, and the VD are measured to analyze the relationship between the AMF arc control and the VD. The optimal AMF arc control and the relationship between the AMF magnitude and the unbalanced voltage ratio are gained when the grading capacitors were 400 pF. The experimental test showed that the proper AMF arc control can improve the unbalanced VD. The mechanism is that the proper AMF arc control can make the postarc charge small and stable, so the unbalanced postarc charge, which caused the unbalanced VD is limited. [ABSTRACT FROM AUTHOR]

The audible noise (AN) production mechanism caused by corona discharge in ultrahigh voltage transmission lines is less understood. The study on sound pressure characteristic is necessary to obtain the inherent relation between AN and corona discharge. In this paper, the experimental research on single-point direct current (dc) corona discharge was evolved and the time-domain sound pressure waveform was obtained using capacitor microphone. The experiment results show that the dc corona discharge comprises multiple subsequent discharge pulses. The discharge voltage and the electrode polarity have a direct effect on the rising time and pulsed width of the single current pulse. The waveform of sound pressure produced by single discharge is a bipolar microsecond pulse, which lags behind the current pulse in time domain. The time delay is propagation time of sound signal from the discharge spot to the measurement spot. Based on the corona discharge characteristic in dc voltage, the experiment platform for nanosecond pulsed discharge was built to obtain the relation between discharge parameter and sound parameter. The characteristics of sound pressure in different discharge conditions were analyzed. The study results indicate that the sound pressure produced by pulsed discharge is similar with that produced by corona discharge. The experiment platform for pulsed discharge can be used to research the AN production mechanism by dc corona discharge. [ABSTRACT FROM AUTHOR]

This paper details the experimental evaluation and simulation of a 4-kV n-type gate turn-OFF thyristor (GTO) designed for pulsed power applications. The primary criteria of evaluation are rate of current rise ( dI/dt ), turn-ON delay time ( T_{D}) , and resistance of the device during turn-ON transients [ R_{\mathrm{\scriptscriptstyle ON}}(t)$ ]. The device under test (DuT) is an n-type asymmetric-blocking GTO manufactured by Silicon Power (Part No. 14N40A10) with a rated dc blocking voltage of 4 kV. A test circuit was specifically designed to minimize stray inductance in order to capitalize on the dI/dt$ capabilities of the DuT. Experimental data collected from resistance measurements are used to develop a single-switch approximate model for use in simulation. The results of dI/dt$ experiments provide a profile of DuT dI/dt$ operation beyond rated values; specifically dI/dt were readily achieved. The turn-ON delay time of the DuT is also characterized and determined to be $\sim 225$ ns on average. [ABSTRACT FROM AUTHOR]

This paper demonstrates the practical application of the explosive magnetic generator (EMG) as a source of high-power pulses for mobile testing complex EMG (MTC EMG). Hereinafter, the name of explosion generator is used on a par with the name of helical explosion-magnetic generator. Laboratory sample was brought to a level of modern complex, which is able to solve the applied problems in the grid power systems. MTC EMG is able to reproduce the output currents, similar to lightning currents, so it can be used to simulate a pulse impact on the energy system. The report contains: a description of the basic physical and electrical solutions underlying the construction of the generator of lightning currents, output characteristics, and results of MTC EMG field testing. Optimization of schemes including the different impedances of EMG and inductive resistive load with the use of transformer coupling allowed the effective energy transfer from the EMG to the load. Pulse currents and voltages on the load and also the response of soil between ground loops under the action of lightning currents, generated by MTC EMG, were registered in the testing. Autonomous measuring instruments included in the complex were protected from electromagnetic interference. [ABSTRACT FROM AUTHOR]

Vacuum arc cathode spot theories are reviewed, beginning from the primary studies in second half of the 19th century up to the present. The evolution of the main ideas is presented, starting from those, which developed, for separate phenomena, up to systematic inclusive models. New spot type classifications are proposed based on observed characteristics, instead of the previous simple numbering. Different approaches were considered for generating plasma comprised of cathode material, based on cathode vaporization and local explosions. Models with closed systems of equations were developed. A kinetic model advantageously allows calculating the cathode potential drop. These closed models explain various phenomena and two base rules were derived: 1) impeded plasma flow enables cathode spot operation and 2) the heat loss in the cathode must be smaller than the energy input to the cathode spot. Based on these rules, mechanisms for the spot types were derived and observed spot behavior in transverse and oblique magnetic fields was described. [ABSTRACT FROM AUTHOR]

Atmospheric-pressure plasma jet (APPJ) array could effectively enlarge the treatment area for the requirement of application efficiency. The downstream uniformity of jet array is the determinant for the even processing effect. In this paper, a three-jet 1-D APPJ array with the electrode structure of needle–ring is constructed, and the position of needle electrode (high-voltage electrode) is adjusted to investigate the influence of electrode arrangement on the downstream uniformity of the 1-D APPJ array. The results show that the relative difference of the positions of the middle and side needle electrodes ${d}$ has great influence on the downstream uniformity. When the distances of the middle and side needle electrodes to the tube nozzles ${a}$ and ${b}$ are both fixed at 40 mm ($d= 0$ mm), the middle plume is suppressed. With increasing the distance of the side needle electrodes to the tube nozzles ${b}$ to make $d=1$ , 2, and 3 mm, the middle plume is prolonged and the lengths of all plumes are almost equal at $d=2$ mm. With the intensified charge-coupled device (ICCD) image measurement, it is found that the desirable synchronicity of bullets propagation is obtained at $d = 2$ mm. The electrical field distributions of different d are simulated, which can be seen that the high electric fields of the side jets can suppress the propagation of middle jet and at $d= 2$ mm, the three jets have similar maximum values of the electrical field strength along the direction of needle electrode resulting in similar plume lengths in the APPJ array. [ABSTRACT FROM AUTHOR]

A new time-domain impedance probe is presented in this paper. The new instrument is able to make measurements of absolute electron density and electron-neutral collision frequency in the ionosphere at temporal and spatial resolutions not previously attained. A single measurement is made in $100~\mu \text{s}$ , which yields an instantaneous spatial resolution of 0.1 m for sounding rocket experiments. A prototype of this instrument was integrated into the payload of a NASA Undergraduate Student Instrument Program sounding rocket launched out of Wallops Island on March 1, 2016. Here, we describe the instrument, and present the data obtained from the sounding rocket experiment. A 6-V amplitude Gaussian derivative excitation was applied to a dipole probe structure, and the current through the probe terminals measured with a balanced active bridge circuit. The time-domain current response was sampled at 5 MS/s, at 12-bit resolution. In the course of the flight, the instrument measured a highly nonlinear response of the plasma because of the large input voltage signal applied. The linear theory cannot explain this response, which obscured interpretation of the data. As a result, we used time- and frequency-domain trend analysis to obtain the variation of electron density over the upleg and downleg of the rocket trajectory. The obtained time and fast Fourier transform trends showed enhanced electron densities in the F layer, which confirmed that the instrument was able to measure the density variations during a significant portion of the flight. [ABSTRACT FROM AUTHOR]

The speed plasma propagates across a charged solar panel after a primary arc is one of the most important, yet poorly known, quantities in determining Electrostatic Discharge (ESD) currents for spacecraft arcing events. A review of the literature over the last two decades reveals that measured propagation velocity varies by as much as an order of magnitude. To overcome this deficiency, a round-robin set of tests was initiated with partners from industry, academia, NASA and the U.S. Air Force. This paper will provide the most recent results from the Air Force Research Laboratory testing conducted at the Spacecraft Charging and Instrument Calibration Laboratory. [ABSTRACT FROM PUBLISHER]

The payload of the four Cluster spacecraft dedicated to multipoint measurements in the earth’s magnetosphere includes ion emitters that can emit currents up to a few tens of microamperes to partially compensate for the photoemission current originating at the spacecraft surfaces and thereby achieve a reduction in the spacecraft potential from values often as high as several tens of volts positive to values well below 10 V. This effect is highly desirable to improve on-board particle measurements, especially of electrons, by reducing the photoelectron flux into the sensors and by reducing the distortions of particle trajectories in the spacecraft sheath. On the other hand, a perfectly stable spacecraft potential precludes the utilization of the spacecraft as a plasma probe, including the useful technique to estimate ambient plasma density from the spacecraft potential. This paper shows that the small residual variations of the potential still allow the determination of ambient plasma density, albeit at reduced accuracy. We present an outline of the applied method with examples. In spring 2002, in the cusp region, the Cluster interspacecraft distances were well below 1000 km. For selected intervals, the potentials of controlled and uncontrolled spacecraft are compared, taking advantage of the fact that the ion emitters were not operating on all spacecraft. Special considerations regarding the secondary electron production and its effect on the controlled spacecraft potential were found to be necessary, and examples of this aspect are presented as well. Finally, the effect of the potential control on the double-probe electric field measurements is assessed. It is found that the normal sun-aligned offset of the electric field caused by the asymmetric spatial distribution of photoelectrons around the spacecraft can be affected by the potential control. Nonetheless, the information about plasma density is not lost when active spacecraft potential control (ASPOC) is applied. This is also relevant for future missions with ASPOC, particularly the NASA Magnetospheric Multiscale mission launched in March 2015. Regular intercalibration of controlled and uncontrolled potentials is nonetheless advisable to increase the reliability of the method. [ABSTRACT FROM PUBLISHER]

Muzzle velocity repeatability of electromagnetic railgun has been identified as a potential development issue for several years. The muzzle velocity is sensitive not only to initial parameters, such as charged voltage of capacitors, mass of armature, and starting position, but also to dynamic parameters, such as electric contact resistance and friction between the armature and rails. This paper analyzes the effects of initial and dynamic parameters on muzzle velocity. It is found that the most sensitive parameter is the charged voltage of capacitors. A series of two 20-shot bursts was performed with two sets of rails, respectively. The details of the experimental setup and velocity measurement are described. The maximum deviation of the muzzle velocity is 3.8% with 8.47-g armatures at a mean velocity of 1913 m/s in the first 20-shot burst, and 0.92% with 10.50-g armatures at a mean velocity of 2373 m/s in the second 20-shot burst. It indicates that the greater armature mass and larger contact area probably advance the repeatability of the railgun muzzle velocity. The effects of rail current and muzzle voltage on repeatability are discussed. The relations between repeatability of the muzzle velocity and the rail current and/or muzzle voltage are not obvious. [ABSTRACT FROM PUBLISHER]

1The transmission of measurement data from the projectile during launch would open up new possibilities for the research with electromagnetic railguns. At the French–German Research Institute of Saint-Louis, a small-caliber railgun projectile is equipped with a commercial off-the-shelf 433-MHz radio transmitter. This transmitter is connected to a microcontroller and a magnetic field sensor. The so equipped projectile is exposed to realistic railgun launch conditions and the transmitted signal is recorded in the laboratory. Here, we report on the implementation of this concept and the first results of the experiments performed with the complete setup.1

This is an extended version of this paper [1]. It is updated by the results of a recent experiment. [ABSTRACT FROM PUBLISHER]

There is considerable need for a mobile, reliable, efficient, and compact prime power supply for use in a host of directed energy applications. Recent improvements in the energy and power density of electrochemical lithium-ion batteries have made them a very viable option for these types of applications where fast and rep-rate operation is of interest. Despite the proven ability of lithium-ion batteries to source high currents, it is still unclear how they age when they are used to repeatedly source high-rate currents in a pulsed manner, as they must when used in a repetitive rate prime power supply. Similarly, it is unclear how elevated rate recharge affects the life of the battery. Research has been performed at University of Texas at Arlington in which high-power, 2.6 Ah lithium-ion batteries have been repeatedly discharged and recharged at high pulsed rates. This paper will discuss the potential of lithium-ion batteries for use in these applications and will present experimental results performed when two 2.6 Ah cells were both discharged at 28 A (10.8C) and recharged at 9 A (3.5C) to 2.5 and 2.0 V, respectively. [ABSTRACT FROM PUBLISHER]

An electromagnetic launcher with a 4.8-MJ pulsed power supply has been fabricated, and experimental tests were started. Through the experiments and calculations, the factors influencing the electrical properties and the performance of the launcher have been investigated. The pulse-forming inductors of the power supply and the rails of the launcher are made of massive conductors showing a prominent skin effect for a transient current. The circuit analysis using constant impedance values has a difficulty in the calculation of the correct voltages between the terminals of the conductors. In addition, the frictional force between the rails and the armature should be considered for a better estimation of the armature motion. To obtain the calculated solutions close to the measured ones, the diffusion of the magnetic flux or current was considered, and the history of the armature motion was reflected in the electrical modeling of the rails. These effects were implemented as voltage correction terms in the circuit equations with the help of the electromagnetic responses to a step-function current. In the equation of the armature motion, a reasonable form of the frictional force was modeled considering the velocity skin effect and the structural analysis. In this paper, the application of the voltage correction method into the rails of an electromagnetic launcher was introduced in detail, and the comparison of the results between the experiments and modified calculations for the constructed launcher system was described. [ABSTRACT FROM PUBLISHER]