Breakdown Time Delay Research Articles

A novel micro-capillary discharge plasma jet triggered gas switch.

To reduce the working coefficient and jitter of the three-electrode gas switch used in linear transformer drivers, a novel trigger method that uses a nanosecond pulse in cooperation with the microplasma jet generated by capillary discharge was developed. A microplasma jet was generated by the nanosecond trigger pulse and injected into the follow-up breakdown gap of the gas switch to decrease the working coefficient. The influence of capillary parameters on the development of the microplasma jet was simulated. The results showed that the microplasma jet significantly reduced the breakdown delay time, jitter, and working coefficient. Increasing the capillary length and decreasing the diameter results in better triggered breakdown performance. Furthermore, the gas switch triggered by a positive pulse exhibits a lower breakdown delay and jitter. Combined with the intensified charge coupled device's shooting results, it can be concluded that the microplasma jet has a distinct influence on streamer formation, which is important for improving the working performance of the gas switch.

Characteristics of electric breakdown in repeated frequency pulse with microcavity effect

The electric breakdown characteristics in microcavity structure under repeated frequency pulse (RFP) were studied, and the physical mechanism was investigated quantitatively based on the full statistical distribution of breakdown time delay obtained in step rectangular pulse (SRP). Experimentally, microcavity heights of 300, 800, and 2000 μm were used. In RFP, the occurrence of breakdown becomes probabilistic when the time delay t d and pulse width t PW satisfy the condition t s-min < t PW < t s-max. The breakdown probability increases with pulse width, and the probability distributions are roughly exponential and Gaussian at pulse frequencies of 3 and 1000 Hz, respectively. We found the results are attributed to the similar distributions of time delay in RFP and SRP with similar afterglow time and pulse voltage, and the equal distributions of breakdown probability (with pulse width) and cumulative probability of t d in RFP. The microcavity effect will decrease the breakdown probability under given pulse width and voltage. Additionally, it is found that in RFP the increase of pulse width from 1 to 1000 μ s will decrease the threshold voltages at 0% and 100% breakdown probabilities, and the threshold voltage difference will decrease simultaneously to around 0, which results in the transition of breakdown feature from probability to certainty. This phenomenon is due to that the reduction of pulse voltage will increase the time delay significantly and meanwhile the variation rate of time delay with pulse voltage Δt d/ΔU w decreases sharply. The microcavity effect will cause the increase of threshold breakdown voltages at a given pulse width and frequency. Finally, it is found that in RFP the breakdown voltage will decrease with the rise of pulse frequency from 10° to 104 Hz, which is consistent with the variation of time delay with afterglow time (from 10−1 to 103 ms) in the memory curve measured in SRP under similar afterglow time. Overall, the microcavity effect will enhance the adsorption of charged and excited species by dielectric walls during afterglow period and enlarge the time delay in the following pulse breakdown, and then influence the RFP breakdown characteristics.

Experimental investigation and theoretical analysis of the breakdown time delay and jitter of multi-gap gas switch gaps.

The gas gap of a multi-gap gas switch can be classified as trigger and self-breakdown gaps based on the breakdown condition. A two-gap gas switch consisting of a trigger gap and a self-breakdown gap is developed to independently study the breakdown characteristics of these two types of switch gaps. Trigger experiments for the switch are conducted under various trigger voltage rise rates and different working coefficients. The experimental results indicate that the trigger gap has significantly more jitter than the self-breakdown gap, and the overall performance of the gas switch is determined primarily by the trigger gap. A novel pre-ionization structure with disks is implemented into the two-gap gas switch, considerably decreasing the breakdown delay of the trigger gap and reducing the jitter to a quarter or even less compared to that without pre-ionization. A calculation model of the breakdown time delay for the trigger gap is provided based on the foundational development of the avalanche. The probability distribution of the time required for the initial electron generation is derived in the absence of pre-ionization. The calculated breakdown time delay agrees well with the experimental results in cases with and without pre-ionization under most trigger settings. The method and principle of calculating the breakdown time delay can analyze the collapse of a gas gap with different electrode configurations (quasi-uniform or uniform electrical fields) and various gas media under a nanosecond pulse voltage.

Hindering breakdown in a long discharge tube by visible spectrum light illumination

The effect of irradiation with visible spectrum light on breakdown in discharge tubes 75–80 cm long and 1.5 cm in inner diameter in rare gases at a pressure of ∼1 Torr was studied. A ramp voltage of variable slope in the range of ∼10–1–105 kV s−1 was applied to the tube anode. The tube was illuminated by radiation from fluorescent lamps operating in a continuous mode, as well as by LEDs or a laser diode operating in a pulsed mode. The breakdown voltage and the pre-breakdown ionization wave (IW) velocity were measured. Illumination led to a change in the breakdown potential. The sign of this change depended on the anode voltage rise rate dU/dt. At dU/dt > 102–103 kV s−1, the breakdown voltage decreased. A similar effect was observed earlier and was explained by the appearance of electrons in the discharge gap under the light action, as a result of which the breakdown delay time decreased. This, in turn, caused a decrease in the breakdown voltage. At dU/dt < 101–102 kV s−1, on the contrary, the breakdown potential increased; at dU/dt ∼ 0.1 kV s−1, this increase could reach 5–6 times. The dependence of the observed effect on the radiation intensity, its wavelength, and the illuminated area position on the tube surface is studied. The pre-breakdown IW behaved in an unusual way under these conditions: its velocity and the signal amplitude recorded by the capacitive probe increased when moving from the high-voltage anode to the cathode. It is assumed that the observed features are caused by the desorption of weakly bound electrons from the tube wall surface under the action of irradiation. These electrons create a current that charges the wall near the anode. Since the first stage of discharge ignition is the initial breakdown between the anode and the tube wall, the anode potential for such a breakdown should increase, which means an increase in the breakdown voltage. Additional experiments with the initiation of a preliminary IW by a pulse applied to the cathode, confirmed the existence of a charge on the wall near the anode.

The effect of initial electrons generation approaches on nanosecond pulsed breakdown characteristics.

In this paper, the effects of initial electrons generation approaches on nanosecond pulsed breakdown characteristics are analyzed. Based on the numerical simulations with a 3D PIC-MCC model, the impacts of field-enhancement factor and initial electron concentration on nanosecond pulsed breakdown characteristics are investigated. Three types of switches are designed and subjected to testing under pulse voltages with rise times of 40, 70, and 120ns, respectively. The results can be summarized as follows. First, the field-enhancement factor and initial electron concentration have significant influences on the development of the discharge channel. Second, the cathode-grooved self-triggered switch exhibits lower breakdown time delay jitter than the hemispherical self-breakdown switch at low pressure, while the differences in jitter between the two switches become negligible at high pressure. Third, the cathode-grooved self-triggered switch shows a lower breakdown time delay jitter compared to the pre-ionization self-triggered switch for pulse voltages with rise times of 40 and 70ns. Conversely, this trend reverses for pulse voltage with a rise time of 120ns. Finally, the breakdown time delay jitter for both the cathode-grooved self-triggered switch and the pre-ionization self-triggered switch has been reduced, and both switches are suitable for different operating requirements and conditions.

COMMERCIAL VOLTAGE INDICATOR AS A GAMMA RADIATION DETECTOR.

The paper analyses the possibility of commercial neon indicator lamp at low pressure application as a gamma radiation detector. The diode is most often used as an indicator in electrical switchers. The analysis was performed on the basis of experimental electrical breakdown time delay data as a function of relaxation time, applied voltage and gamma ray air kerma rate. It has been shown that the indicator can be used as a detector for relaxation time greater than 70ms. During this time period, a complete recombination/de-excitation of the particles formed during previous breakdown and subsequent self-sustaining discharge, which can further initiate next breakdown, takes place. It was also shown that gamma radiation leads to a significant reduction in electrical breakdown time delay for applied voltages close to indicator breakdown voltage. Based on the behavior of the dependence of the mean value of the electrical breakdown time delay on the gamma ray air kerma rate, it was shown that the indicator can be used very efficiently as a detector up to air kerma rate of $\textsf{2.3}\cdot \textsf{10}^{-\textsf{5}}$Gy/h, when the electrical breakdown time delay is measured for applied voltage 10% higher than the breakdown voltage.

Investigation of the Dielectric Properties of the Insulating Gas of Commercial Gas-Filled Surge Arresters

Based on the experimental results of dynamic breakdown voltage and electrical breakdown time delay, the dielectric properties of insulating gas commercial gas-filled surge arresters were analyzed. Data for dynamic breakdown voltage obtained by the method of stepwise increase of voltage whose rise rates ranged from 1 to 10 V/s. It is shown that these values of voltage rise rate do not have a significant effect on the value of dynamic breakdown voltage. In order to monitor the processes caused by electrical breakdown on the dielectric properties of insulating gas of these components the electrical breakdown time delay was a measure for different values of relaxation time and applied voltage. It has been shown that the presence of positive ions, which are formed during breakdown and subsequent self-sustaining discharge with recombination time of about 1 ms, has a significant effect on the reduction the dielectric resistance of insulating gas. It has also been shown that the applied voltage whose values are close to DC-spark over-voltage has a significant effect on the delay response of these components.

The effects of pulse voltage rise time on the nanosecond pulsed breakdown of nitrogen spark switch at atmospheric pressure with 3D PIC-MCC model

In this paper, the effects of pulse voltage rise time on the nanosecond pulsed breakdown of the nitrogen spark switch at atmospheric pressure are analyzed. Based on the assumption of initial electrons generation due to the field emission, the simulations are performed using a three-dimensional particle-in-cell, Monte Carlo-collision model for the pulse voltage with a rise time of 40, 60, and 100 ns, respectively. The breakdown experiments of the nitrogen spark switch are carried out for three different rise times. The results obtained are as follows. First, the nanosecond pulsed breakdown of the switch includes the formation and fast propagation of the streamer, which depend on the multiplication of the electron avalanche, and the intense ionization due to photoelectrons and energetic electrons, respectively. Second, with the rise time of pulse voltage increasing, the generation of runaway electrons becomes more difficult and the streamer branches, which are mainly caused by photoionization and captured energetic electrons, become more obvious. Finally, the breakdown time delay of the switch becomes shorter and the breakdown voltage becomes higher at the same pressure for the decreasing rise time of pulse voltage, which is consistent with the measurement results.

Simulation of the statistical and formative time delay of Townsend‐mechanism‐governed breakdown in argon at low pressure

AbstractUnderstanding the breakdown process is important both from fundamental and practical perspectives. One of the most important quantities that characterize the breakdown is the breakdown time delay. In this article, numerical models for self‐consistent simulation of the statistical and formative time delay of the electric breakdown in argon at low pressure have been proposed. The first model, based on the Monte Carlo simulation of the electron avalanche development, is used to simulate the statistical time delay. The model is designed for low‐pressure breakdowns when the Townsend mechanism is dominant. The electric breakdown is then governed by ion‐induced secondary electron emission from the cathode. In that case, the statistical time delay to breakdown is determined by tracking the waiting time of emission of the primary electron that initiates the electron avalanche and the number of ions produced in it. On the other hand, the formative time delay is determined by simulating the electric current waveform using the fluid model. To test whether the proposed models can be used for discharges operating under various conditions, the voltage dependence is simulated for both the statistical and the formative time delay. The results of the simulations show good agreement with the experimental results and theoretical models.

Investigation of the Influence of Technological Operating Conditions of Electric Discharge Installations on the Pre-Breakdown Characteristics of an Electric Discharge

This work deals with the influence of the parameters of the working fluid (hydrostatic pressure, temperature, electrical conductivity) and the geometry of the electrode system (the length of the interelectrode gap and the uninsulated part of the anode) on the pre-breakdown characteristics of an electric discharge in a liquid aqueous electrolyte (breakdown voltage and breakdown delay time) and the minimum charging voltage, which provides a stable high-voltage breakdown of the interelectrode gap. Studies have shown that an increase in the hydrostatic pressure leads to an increase in most of the studied characteristics. At the same time, an increase in the specific electrical conductivity and temperature was observed to lead to their decrease. At the same time, it was suggested that the effect of temperature on the pre-breakdown characteristics is associated with a change in the specific electrical conductivity of the working fluid during its heating. The data obtained showed no effect of the length of the interelectrode gap on the breakdown voltage and its breakdown delay time, as well as the minimum charging voltage. The results of the experimental studies made it possible to develop a criterion for determining the charging voltage, which provides a stable high-voltage breakdown of the water interelectrode gap. Its experimental verification has shown that it can be applied to the design of electric discharge equipment and to the choice of technological modes of operation in the specified range of parameters.

Influence of low dose rate gamma radiation on breakdown voltage and electrical breakdown time delay of working gas Geiger-Muller chamber

This paper presents the experimental data on the dynamic breakdown voltage and electrical breakdown time delay of commercial Geiger-Muller chamber manufactured by PHILIPS. The distributions of these data were determined. Static breakdown voltage was estimated based on the mean value of dynamic breakdown voltage as the function of voltage increase rate, for the cases when gamma radiation was not presented and in its presence. In order to separate the mechanisms that predominantly influence the initiation of breakdown for different values of relaxation time, the dependences of mean value of electrical breakdown time delay as the function of relaxation time was analyzed. It has been shown that during the relaxation times up to 3 ms positive ions plays a dominant role in initiating the breakdown while for relaxation times from 3 ms to 30 s initiation of the breakdown is caused by electrically neutral active particles. The effect of gamma radiation on electrical breakdown time delay was observed for relaxation time greater than 7 s.

Xenon-filled diode performance under influence of low doses of gamma radiation

This paper presents a detailed statistical analysis of experimental results of dynamic breakdown voltage and electrical breakdown time delay for xenon-filled diode. These quantities have a stochastic nature and they were measured in the cases when the xenon-filled diode was and was not exposed to a gamma radiation source, with exposure dose rate 7.7⋅10−12 C/(kg⋅s). The static breakdown voltage was estimated based on dynamic breakdown voltage as a function of voltage increase rate. The applicability of certain distributions to experimental dynamic breakdown voltage and electrical breakdown time delay data was also analyzed.

Analysis of soil impulse discharge characteristics based on optical‐electrical synchronous observation

The impulse performance of grounding electrodes highly depends on soil impulse discharge characteristics. The analysis of soil discharge dynamic process images is helpful to understand the impulse discharge mechanism of grounding electrodes. This paper designed an optical-electrical synchronous observation platform for simulate soil (SiO2 crystal) discharge, and discharge dynamic process images is obtained by high-speed camera. Through analysing breakdown delay time and thermal power before breakdown, it is found that soil impulse discharge is mainly an electrical breakdown process, and soil ionization intensity is positively correlated with the light intensity emitted by whole soil sample in breakdown channel development stage. The time from voltage application to the occurrence of ionization is defined as initial ionization delay time (IIDT). Using image processing technology, the change curve of optical image average grayscale value with time in the process of soil discharge is obtained, and a calculation method of IIDT is proposed by comparing the difference between average grayscale value curve and background image average grayscale value. Experiment results show that IIDT is negatively correlated with impulse voltage, particle size and water content, but not with salt content.

Controlling the breakdown delay time in pulsed gas discharge

In experiment and 2D3V PIC MCC simulations, the breakdown development in a pulsed discharge in helium is studied for U = 3.2 kV and 10 kV and P = 100 Torr. The breakdown process is found to have a stochastic nature, and the electron avalanche develops in different experimental and simulation runs with time delays ranging from 0.3 to 8 μs. Nevertheless our experiments demonstrate that the breakdown delay time distribution can be controlled with a change of the pulse discharge frequency. The simulation results show that the breakdown process can be distinguished in three stages with (a) the ionization by seed electrons, (b) the ions drift to the cathode and (c) the enhanced ionization within the cathode sheath by the electrons emitted from the cathode. The effects of variation of seed electron concentrations, voltage rise times, voltage amplitudes and ion–electron emission coefficients on the breakdown development in the pulsed gas discharge are reported.

Influence of Glow and Afterglow Times on the Discharge Current of Argon at Low Pressure

An experimental investigation of the variation of argon discharge current with a glow and afterglow time intervals of a square discharge voltage was carried out at low pressure (6-11 mbar). The discharge was created between two circular metal electrodes of diameter (7.5 cm), separated horizontally by a distance (10 cm) at the two ends of a Pyrex cylindrical tube. A composite of two Gaussian functions has been suggested to fit and explain the variation graphs clearly. It is shown that the necessary times of glow and afterglow needed to attain a maximum discharge current are (70 us) and (60 us), respectively. The discharge current is observed to drop to the lowest value when the two times are serially longer than (85 us) and (72 us). Furthermore, the difference between the two times required to obtain a maximum rate of change in the discharge current, or a maximum discharge current, is deduced to be comparable to the breakdown time delay of gases reported in the literature. These observations can be useful for the design of plasma devices requiring specialized engineering.

A calculation model for breakdown time delay and jitter of gas switches under hundred-nanosecond pulses and its application in a self-triggered pre-ionized switch

In this paper, a calculation model for the breakdown time delay and jitter of gas switches under hundred-nanosecond pulses is proposed and applied in a self-triggered pre-ionized switch. The effects of injection time of pre-ionization, pulse rise time, and the pre-ionization jitter are discussed and verified through experiments. It indicates that the pre-ionization should be injected when the electric field is high enough in the gap, injection after 80% peak-time can ensure its effectiveness. Then the statistical time delay jitter will be determined by the pre-ionization jitter, which is an intrinsic restriction of the self-triggered switch. However, when the changing rate of the pulsed electric field exceeds a certain value, the breakdown time delay jitter can be partly offset in the formative stage because the formative time delay has an exponential relationship with the electric field. Therefore, lower time jitter can be obtained under pulses with a shorter pulse rise time. In general, the results of the calculation model agree with the experimental results, and the experimental parameters which lead to a low jitter can also be used as a reference.

A low-jitter self-triggered spark-discharge pre-ionization switch: primary research on its breakdown characteristics and working mechanisms

MV pulsed switch plays a key role as the transfer switch in large electromagnetic pulse simulators. To broaden the range of self-triggering time, a novel spark-discharge pre-ionization switch, in which the main gap electric field is superposed at the trigger gap to let the electrons in its spark channel also become initial electrons, is proposed and tested. The design idea is: as electrons in the spark channel of the trigger gap always exist after its breakdown, the injection time of pre-ionization should have a more negligible effect on reducing the switch jitter. The experiment results under pulses with a rise time of ∼100 ns support the above assumptions. When the operating voltage is from ∼300 to ∼800 kV and the self-triggering time is ∼45% to ∼75% of the peak time, the breakdown time delay jitter is less than 2 ns, and the breakdown voltage jitter is smaller than 1.25%. Under specific self-triggering time, the breakdown time delay jitter is less than 1.5 ns, and the breakdown voltage jitter is smaller than 0.8%.

The effects of air flow on the nanosecond pulsed pin-to-pin discharge dynamics in atmosphere-pressure air

Investigation of the breakdown phase of a nanosecond pulsed pin-to-pin discharge in air at atmosphere pressure with different gas flow rates is carried out. The experimental results show that the air flow leads to increase in the breakdown delay time. The effect of air flow rate on the current growth rates and streamer channel appearance at the beginning of breakdown is observed, which indicates that the redistribution and decrease in the densities of reactive species produced by previous discharges are playing the main role in the discharge delay time. When 15 standard liters per minute (slm) air flow is used and pulse frequency is 1 kHz, the discharge current reaches a peak of about 0.5 A, then it decreases to 0.4 A and lasts for about 70 ns, and then the discharge current starts to increase rapidly at a rate of &amp;gt;0.1 A/ns. For pulse frequency of 8 kHz or nitrogen as working gas, the discharge current increases monotonically. Besides, the difference of the gas temperature for the cases of 0 and 15 slm is measured, and the result indicates that the difference of the gas temperature should not be the main contributor to the difference of the breakdown delay time. Detailed analysis shows that the appearance of the first current peak is due to the fast detachment of O2−. Finally, simulation results show that the ionization rate for the case of 15 slm is also more significantly delayed than the case of 0 slm, which is consistent with the measured discharge current waveform.

Lightning Impulse Long Delay Breakdown of Centimeter Vacuum Gaps

This paper presents an experimental investigation into the breakdown voltage fall time tf of lightning voltage breakdown of 2-4 centimeter vacuum gaps having a long breakdown delay time td(>30 μs). The results show that the average 50% breakdown voltage fall time t50 decreases with increasing vacuum gap. It is considered that the lightning impulse breakdown of the centimeter vacuum gaps with a long breakdown delay time may be initiated by the interaction between the cathode thermal processes and the micro-particles phenomena. The increase of the electrode diameter and the decrease of the electrode radius of curvature may contribute to the decrease of the breakdown voltage fall time.

Study on the characteristics of helium plasma jet by pulsed micro-hollow cathode discharge

In this paper, the helium plasma jet generated by micro-hollow cathode discharge (MHCD) was studied. The MHCD was driven by a square-wave pulsed power source, and the characteristics of discharge and plasma jet were measured experimentally. The influences of the gas flow rate on the MHCD and the plasma jet were investigated. And the propagation mechanisms of the plasma jet were analyzed. The results show that within 100–1000 sccm of the gas flow rate, the breakdown delay time of the MHCD increases with the helium flow increasing. It is considered that the gas flow affects the density of seed electrons and thus the breakdown delay time. With the helium flow rate increasing, the whole plasma jet length increases firstly and then decreases. A detailed investigation shows that during one discharge pulse, two distinguishable propagation processes of the plasma jet are observed. It is found that the jet of the first stage is formed during the rising edge of the current pulse, while the other is generated after the discharge current becomes stable. The propagation velocity of jet in the first stage is on the order of several km s−1, which is similar to that of the discharge evolution obtained by simulation. And the propagation speed of the jet in the second stage is on the order of several hundred m s−1, which is close to the velocity of gas flow. The spatial–temporal distributions of light emission show that high-energy electrons can only be observed during the jet propagation in the first stage, and low-energy electrons can be detected in both the first and second stages. The results show that the electric field plays an important role on the jet propagation in the first stage, and the jet propagation during the second stage is mainly promoted by the thermal gas expansion.