Rise Time Of Voltage Pulse Research Articles

Design of a High Speed Electro-optic Q-switch Circuit for Aerospace Applications

In order to meet the requirements of high amplitude and high speed of electro-optic Q-switch voltage, a high speed electro-optic Q-switch circuit for aerospace applications is designed. According to the principle of Marx generator, the circuit uses a high speed driving chip to drive the switching transistor to conduct. The charge of the primary energy storage capacitor of the pulse transformer is quickly released, and the secondary induced voltage drives the switches of the Marx generator to open quickly and synchronously. By utilizing the fast and synchronous opening of MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), cascaded discharge is carried out on the energy storage capacitors of the 8th order Marx generator circuit, thereby outputting high voltage pulse signal. The experimental results show that the Marx generator has maximum boost output range of 4000V and high voltage pulse rise time of less than 30ns. Compared to traditional pulse transformer control methods, the Q-switch voltage rise time is reduced by nearly 40ns. The internal components of circuit meet the requirements of multiple indicators such as anti-irradiation space environment, and have the characteristic of short output high voltage rise time, which can provide high speed and high voltage driving pulses for the electro-optic Q-switch crystal inside the laser cavity.

Определение потерь в стали бесконтактного двигателя постоянного тока с использованием линейной аппроксимации импульсов напряжения

Analysis of iron loss of a BLDC motor is of particular interest at the design stage or when researching methods to improve energy efficiency. Most of the existing methods for determining losses in steel are based on the analysis of losses for individual harmonic components of induction with their subsequent summation. However, the application of these methods for various forms of voltage obtained at the output of the converter is incorrect due to the non-linearity of magnetic circuits. This paper proposes a method for determining steel losses of BLDC motor using a linear approximation of voltage pulses, which makes it possible to take into account the influence of the voltage shape on the magnitude of magnetic induction directly, without expansion into a Fourier series. The dependences of steel losses on the switching frequency for various values of the duty cycle, and on the rise time of voltage pulses are obtained. Comparison of the simulation results of the 5 kW BLDC Motor with the experimental data of the idling mode given by the manufacturer proved the adequacy of the considered method.

Electronic mechanism of propagation of nanosecond breakdown channel in liquid organic dielectrics

The mechanism of anode-initiated breakdown in liquid organic dielectrics with long molecular chains is proposed on the basis of the experimental data on high velocities of the breakdown channel propagation in organosilicon and organofluorine liquids (~107 cm/s), which are comparable to that obtained earlier in crystals in the same conditions. The high velocities of the anode-initiated breakdown channel are satisfactory explained within the model of the cascade Auger transitions, developed for the crystalline materials. According to this model, velocity of the breakdown channel propagation is proportional to the electrical field strength. The time delay in breakdown channel formation relative to the voltage pulse rise time does not exceed ~5·10-10 s within the margin of error Keywords: electrical breakdown in liquid, nanosecond breakdown, breakdown mechanism.

Формирование двух импульсов тока пучка убегающих электронов

The conditions for the formation of two current pulses of runaway electron beams during the breakdown of a point-to-plane and tube-to-plane gaps in high-pressure air, nitrogen, and helium are studied. It has been shown experimentally that, depending on a pressure and kind of gas, a rise time of voltage pulse with an amplitude of tens of kilovolts, three modes of generation of runaway electron beams are observed. In the first mode, a single current pulse of runaway electron beam is observed at the maximum voltage across the gap, when a streamer appears in the vicinity of the pointed electrode (cathode). Its duration is ≈100 ps. In the second mode, two current pulses of runaway electron beams are observed at a lower pressure. The first pulse is generated as in the first mode. The second pulse is generated after the gap is bridged by the streamer (the first ionization wave). The electron energy in the second pulse is significantly less than in the first one, but the duration and amplitude of second current pulse under optimal conditions are greater. The third mode is implemented at lower pressures than in the second one. The generation of runaway electrons continues after the first pulse without a pause in the quasi-stationary stage. The total current pulse duration is hundreds of picoseconds.

Partial Discharge Analysis under High-Frequency, Fast-Rise Square Wave Voltages in Silicone Gel: A Modeling Approach

Wide bandgap (WBG) power modules able to tolerate high voltages and currents are the most promising solution to reduce the size and weight of the power management and conversion systems. These systems are envisioned to be widely used in the power grid and the next generation of more (and possibly all) electric aircraft, ships, and vehicles. However, accelerated aging of silicone gel when being exposed to high frequency causes fast rise-time voltage pulses that can offset or even be an obstacle for using WBG-based systems. Silicone gel is used to insulate conductor parts in the module and encapsulate the module. It has less electrical insulation strength than the substrate and is susceptible to partial discharges (PDs). PDs often occur in the cavities located close to high electric field regions around the sharp edges of metallization in the gel. The vulnerability of silicone gel to PDs occurred in the cavities under repetitive pulses with a high slew rate investigated in this paper. The objective mentioned above is achieved by developing a Finite-Element Analysis (FEA) PD model for fast, repetitive voltage pulses, which have been done for the first time to the best of our knowledge. By using the model, the influence of frequency and slew rate on the magnitude and rate of PD events is studied.

On the influence of a cathode shape on the parameters of current pulses of runaway electron beams in a gas discharge when applying voltage pulses with a rise time of 200 ns

The influence of the shape of a cathode on the duration and amplitude of a supershort avalanches electron beam (SAEB) current pulses was experimentally studied. Three cathodes were used in experiments: tube, needle, and ball. Voltage pulses with a rise time of 200 ns were applied across an 8.5 mm gap filled with air and nitrogen at various pressures (12.5–100 kPa). It was found that at an air pressure of 12.5 kPa and a rise time of voltage pulses 200 ns, the largest amplitudes of SAEB current pulses (90 mA) were observed with the tubular cathode. The SAEB current pulse duration was τ0.5 ~ 130 ps. Two pulses with different duration, amplitude and energy of electrons were observed with the needle cathode at same pressure. When using the ball cathode, the duration and amplitude of the beam current pulses were τ0.5 ~ 250 ps and ~ 4 mA, respectively.

Influence of voltage pulse rise-time on initiation and propagation of fast ionization waves in extended capillaries

Creating stable and efficient compact X-ray sources based on fast capillary discharges that do not incorporate preliminary ionization circuits poses additional restrictions on parameters of voltage pulses and capillary geometry. Applying a voltage pulse with a rise rate of the order of 1 kV/ns results in gradual breakdown of non-ionized gas in the capillary which takes the form of an ionization wave that initiates at the powered electrode and propagates with typical velocities of 1 cm/ns. After the wave reaches the grounded electrode, a plasma channel with gradually increasing conductivity is formed. The current onset therefore appears only after a certain time delay after beginning of the voltage pulse. The ratio between the delay and the applied voltage rise-time will eventually influence the current rise rate that defines plasma heating and compression. It is therefore necessary to have the ability to estimate this delay time for a given capillary geometry and understand its dependence on the properties of a voltage pulse. In this work numerical simulations of fast ionization waves created in an extended Al2O3 capillary filled with nitrogen at 2 Torr were performed for cases of voltage pulses of negative polarity with rise-times varying in the range 10-50 ns. The numerical model was based on fluid approach with drift-diffusion approximation for charged particle fluxes. Influence of voltage rise-time on initiation and propagation of a fast ionization wave as well as on consequent rate of current rise is investigated.

Research on optimum slowly-rising driver for electro-optic Q-switched laser

Electro-optic Q-switch drivers that based on pulse transformer method have been widely used in laser engineering because of the advantages of concise circuits, low supply voltage, low lost, etc., but the long rise time and short pulse duration of the high voltage (HV) pulses have a considerable effect on the Q-switched laser outputs. In this paper, we experimentally investigated the dependence of Q-switched laser outputs on the rise rate of slowly-rising HV pulses in a flash pumped Nd:YAG laser with variable cavity lengths. LiNbO3 Q-switches with various dimensions were used. Based on the experiment results, the optimum slowly-rising HV pulses for any EO Q-switched laser were derived, the only requirement is that voltage near dynamic quarter-wave voltage during the emission of laser pulses. Additionally, the optimum outputs were found to be consistent with the results obtained by using a rapid-switching driver with a rise time of 7 ns. The optimum range of applied voltage was determined to be 0.88–1.12 times dynamic quarter-wave voltage.

Uniformity analysis of nanosecond and sub-nanosecond pulsed DBD in atmospheric air

In this study we report the results of atmospheric air nanosecond-pulsed dielectric barrier discharge (DBD) uniformity analysis as a function of applied electric field. We quantify the uniformity of the discharge by analyzing the discharge images obtained with fast intensified charge-coupled device camera using chi-square test. The results show that uniformity of DBD strongly depends on applied electric field with a weak effect on the high voltage pulse rise time. The nanosecond-pulsed air DBD operates in two distinct modes, namely, non-uniform streamer regime and uniform ‘overvoltage’ regime, with transition applied electric field of around 130 kV cm−1.

X-ray radiation and runaway electron beams generated during discharges in atmospheric-pressure air at rise times of voltage pulse of 500 and 50 ns

AbstractThe parameters of X-ray radiation and runaway electron beams (RAEBs) generated at long-pulse discharges in atmospheric-pressure air were investigated. In the experiments, high-voltage pulses with the rise times of 500 and 50 ns were applied to an interelectrode gap. The gap geometry provided non-uniform distribution of the electric field strength. It was founded that at the voltage pulse rise time of 500 ns and the maximum breakdown voltage Um for 1 cm-length gap, a duration [full width at half maximum (FWHM)] of a RAEB current pulse shrinks to 0.1 ns. A decrease in the breakdown voltage under conditions of a diffuse discharge leads to an increase in the FWHM duration of the electron beam current pulse up to several nanoseconds. It was shown that when the rise time of the voltage pulse is of 500 ns and the diffuse discharge occurs in the gap, the FWHM duration of the X-ray radiation pulse can reach ≈100 ns. It was established that at a pulse-periodic diffuse discharge fed by high-voltage pulses with the rise time of 50 ns, an energy of X-ray quanta and their number increase with increasing breakdown voltage. Wherein the parameter Um/pd is saved.

Fast Rise Time High Current Electron Beam: Emission, Acceleration, and Drift Motion

Fast processes associated with emission, acceleration, and drift motion of a high current, moderately magnetized electron beam (particles energy ~300 keV; current ~3 kA) were studied experimentally when tubular explosive-emission cathode was supplied by subnanosecond rise time voltage pulse. Kinematic effect causes the sharpening of the observed beam front which was proven by particle-in-cell numerical modeling. The angular structure of tubular beam was studied through the current waveform records from collector probe after beam propagation through a radial-slit collimator. Current waveforms had time resolution no worse than 10 ps and provided the analysis of the beam temporal structure after its acceleration as well as in the process of further electrons drift motion in a finite guiding magnetic field.

Performance characteristics of an excimer laser (XeCl) with single-stage magnetic pulse compression

Performance characteristics of an excimer laser (XeCl) with single-stage magnetic pulse compression suitable for material processing applications are presented here. The laser incorporates in-built compact gas circulation and gas cooling to ensure fresh gas mixture between the electrodes for repetitive operation. A magnetically coupled tangential blower is used for gas circulation inside the laser chamber for repetitive operation. The exciter consists of C–C energy transfer circuit and thyratron is used as a high-voltage main switch with single-stage magnetic pulse compression (MPC) between thyratron and the laser electrodes. Low inductance of the laser head and uniform and intense pre-ionization are the main features of the electric circuit used in the laser. A 250 ns rise time voltage pulse was compressed to 100 ns duration with a single-stage magnetic pulse compressor using Ni–Zn ferrite cores. The laser can generate about 150 mJ at ∼100 Hz rep-rate reliably from a discharge volume of 100 cm 3. 2D spatial laser beam profile generated is presented here. The profile shows that the laser beam is completely filled with flat-top which is suitable for material processing applications. The SEM image of the microhole generated on copper target is presented here.

Runaway electrons during subnanosecond breakdowns in high‐pressure gases

The parameters of runaway electrons produced in nanosecond high-voltage discharges in different gases (air, nitrogen, sulphur hexafluoride, krypton, argon, methane, neon, hydrogen, helium) at atmospheric and higher pressure were studied. An optical analysis was also performed to investigate the ionisation dynamics in diffuse discharges in nitrogen and nitrogen-containing mixtures. At breakdown of a point-to-plane gap by nanosecond (≃2 ns) high-voltage (≃200 kV) pulses of negative voltage polarity and gas pressure above 0.1 MPa, a supershort avalanche electron beam (SAEB) was detected by a collector behind the flat anode. For pressure >0.1 MPa of nitrogen and other gases it is shown that the maximum pressure for SAEB registration decreases with increasing the voltage pulse rise time. Therefore, to detect a SAEB at atmospheric and higher gas pressure, one should use voltage pulses with an amplitude of hundred kilovolts and rise time of ∼1 ns and shorter. The experimental research in the dynamics of optical radiation from the discharge plasma shows that the breakdown in which runaway electrons are produced develops as an ionisation wave.

Rise time of voltage pulses in NbN superconducting single photon detectors

We have found experimentally that the rise time of voltage pulse in NbN superconducting single photon detectors increases nonlinearly with increasing the length of the detector L. The effect is connected with dependence of resistance of the detector Rn, which appears after photon absorption, on its kinetic inductance Lk and, hence, on the length of the detector. This conclusion is confirmed by our calculations in the framework of two temperature model.

Breakdown features of a high-voltage nanosecond discharge initiated with runaway electrons at subnanosecond voltage pulse rise time

In the wide pressure range of the pure nitrogen and sulfur hexafluoride with small admixture of nitrogen (2,5%) the development of the breakdown during the formation of diffuse discharges initiated by runaway electrons and X-Ray was investigated. Nanosecond voltage pulses of both polarities with an amplitude up to ~300 kV and risetime of ~0.5 ns applied across the discharge gap did provide sharply nonuniform electric field distribution. Estimations of average propagation velocity of the ionization wave in the nitrogen and mixture sulfur hexafluoride with nitrogen were performed on the basis of data on dynamics of radiation intensity of the second positive (2+) nitrogen system from various regions along of the longitudinal axis of interelectrode gap. Interrelation between the glow dynamics and the local value of the electric field strength has been defined. The results showed that the breakdown is developed in the form of the ionization wave propagating from the potential electrode with the highest concentration of the electric field to the flat-grounded one. In the regions near the grounded electrode practically simultaneous increasing of radiation intensity is registered, that indicates on a possible change of the breakdown mechanism in this part of the discharge gap.

Nitric oxide PLIF measurement in a point-to-plane pulsed discharge in vitiated air of a propane/air flame

The effect of a point-to-plane pulsed discharge on the vitiated downstream of a propane/air flame has been investigated by phase-locked NO planar laser-induced-fluorescence (PLIF) measurements. Phase-locked NO PLIF measurements with the variation of pulsed plasma energy, equivalence ratio and applied voltage rise time have been performed. Fast rise time (25 ns) and slower rise time (150 ns) high-voltage pulsers are used to produce NO radical densities greater than the ambient flame-produced NO radicals in lean, balanced and rich premixed flames. The pulsed plasma produced excess NO radical densities were found to decay to 50% level with time constants greater than 250 µs in the burnt gas regions with gas temperatures greater than 1000 K. The super-equilibrium NO populations were dependent on energy deposited and overall equivalence ratio, but independent of voltage pulse rise time for similar energy deposition per pulse. Due to long NO radical density decay lifetimes, super-equilibrium NO populations are convected away from production regions with the ambient flow and observed in downstream exhaust gas regions.

Abnormal polarity effect in nanosecond-pulse breakdown of SF6 and nitrogen

Abstract The breakdown of gas gaps in an inhomogeneous electric field at subnanosecond and nanosecond voltage pulse rise times are studied, and the famous polarity effect in point-to-plane gaps is investigated. It is shown that at a voltage pulse rise time of ∼0.5 ns, the inversion of polarity effect takes place not only in electronegative gases such as SF6, but also occurs in electropositive nitrogen. The inversion of polarity effect is related to a delay of electron emission from the plane cathode on arrival of the ionization wave front anode to the cathode. It is found that with a voltage pulse rise time of ∼0.5 ns, the inversion of polarity effect occurs at SF6 and SF6–N2 pressures of 0.25 MPa and lower, and with a voltage pulse rise time of 15 ns, at a SF6 pressure lower than 0.12 MPa.

Generation of electron beams with adjustable durations of 1.0–0.2 ns and current amplitudes more than 400 A

The conditions for forming subnanosecond electron beams with adjustable pulse durations in the vacuum-diode mode using a SLEP-150 generator were investigated. It was confirmed that the residual air pressure in the diode (∼0.1 Torr or less) does not affect the amplitude and duration of the beam current when using a nanosecond voltage pulse. It was shown that increasing the air pressure in the diode from 0.1 to 6.0 Torr leads to a decrease in the full width at half-maximum (FWHM) duration of the electron-beam current from ∼1.00 to 0.18 ns and a shorter delay of the beam generation moment relative to the voltage-pulse rise time. It was established that the amplitude of the first peak of the beam current behind the foil remained constant under these conditions. Its value was ≥400 A. It is shown that when the interelectrode gaps are optimal for vacuum diodes, the pulse duration at elevated pressures shortens due to the gap breakdown for a time of ≤200 ps.

Gradual Tuning of the Current Pulse Width Within 1-0.03 ns in Gas-Filled Diodes of Nanosecond Electron Accelerators

The conditions for the generation of subnanosecond and picosecond electron beams with a tunable pulse width are studied on an SLEP-150 generator with a tubular cathode at a voltage pulse rise time of 0.3 ns. The width and shape of the beam current pulse are varied by varying the pressure and gas kind in the diode. It is shown that in the vacuum diode mode, the beam current rise time decreases from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\sim}{0.5}$</tex></formula> to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 0.2}~{\rm ns}$</tex></formula> as the interelectrode gap is decreased from 12 to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 2}~{\rm mm}$</tex> </formula> . It is found that with a 3-mm interelectrode gap, increasing the air pressure in the diode of the SLEP-150 generator from 0.1 to 6 torr decreases the full width at half maximum (FWHM) of the current pulse from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{1}$</tex></formula> to 0.18 ns, with the beam current amplitude greater than 400 A and the beam current rise time less delayed with respect to the voltage pulse rise time. It is confirmed that with a nanosecond voltage pulse, the residual pressure of helium, nitrogen, and air in the diode ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{0.1}$</tex></formula> torr or less) does not affect the beam current amplitude and pulse width. At low pressure of air in the gas diode, the attained beam current density at a beam current pulse FWHM of 0.18-1 and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 0.1}~{\rm ns}$</tex></formula> is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{500}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\sim}{100}~{\rm A}/{\rm cm}^{2}$</tex></formula> , respectively.

Breakdown of gas gaps in a nonuniform electric field at a subnanosecond voltage pulse rise time

The influence of the nitrogen pressure on the breakdown voltage in a nonuniform electric field is studied. Voltage pulses with nanosecond and subnanosecond rise times are applied to the gas gap. Simultaneously with the application of voltage pulses, supershort avalanche electron beam pulses are observed behind a foil anode. It is found that, when a runaway electron beam is generated and voltage pulses have a subnano-second rise time, the breakdown voltage rises as the nitrogen pressure decreases from 9 × 104 to 1 × 102 Pa. Experimental data are in good agreement with pulsed breakdown analytical curves.