Rise Time Of Voltage Pulse Research Articles

Subnanosecond Semiconductor Opening Switch Based on 4H-SiC Junction Diode

Mesa-epitaxial 4H-SiC p+-p-no-n+-diodes were fabricated and their reverse recovery characteristics were measured in pulse regimes to be relevant to DSRD- and SOS-modes of operation [I.V. Grekhov, G.A. Mesyats, Physical basis for high-power semiconductor nanosecond opening switches, IEEE Transactions on Plasma Science 28 (2000) 1540-1544]. It has been found that after short pumping the diodes by forward current pulse (5-ns duration, 200-A/cm2 peak current density) followed by applying the reverse voltage pulse (rise time 2 ns) the diodes are able to interrupt the reverse current density of 3.5 - 25 kA/cm2 in a time less than 0.3 ns.

An adaptive hysteresis dead-band-based SVPWM method for multi-level inverter

The fast rise time of output voltage pulses (dv/dt) in PWM multi-level inverters (MLI) is one of the major factors of the increase of electromagnetic interference EMI and the shortness of motor useful life. Moreover, irregular voltage pulses, which only appear for critical modulation indexes, can deepen this interference phenomenon. To overcome this problem, this paper proposes an adaptive hysteresis dead-band (AHDB)-based space vector PWM (SVPWM) method for MLI. The proposed scheme is developed for multilevel cascaded H-bridge (CHB) inverters. In the proposed strategy, general dwell-time equations were derived to achieve the SVPWM for any n-level inverter. Moreover, the dwell-times calculation was made easy by using only two parameters defining regions for a given sector. Furthermore, to remove all irregular pulses from the output voltage, the dead-band of the hysteresis was made variable. Both theoretical analyses and simulation results are presented to show the effectiveness of the proposed method.

Simulation of the formation of a runaway electron beam in an overvolted gas gap breakdown

The paper reports on numerical simulation to inquire into the breakdown of a gas-filled diode in a highly inhomogeneous electric field. It is shown that early in the breakdown a runaway electron beam (RAEB) is formed in the diode and this strongly affects the rate of breakdown development. The energy gained by RAEB electrons corresponds to the electron energy gained under the same conditions in vacuum. The properties of the emission surface of the cathode determine the instant at which the beam is formed during subnanosecond voltage pulse rise time and hence the beam current and the energy spectrum of runaway electrons.

Spark discharge formation in an inhomogeneous electric field under conditions of runaway electron generation

In this article we report on work where the formation of a spark in nanosecond high-voltage discharges was studied in nitrogen, nitrogen-methane mixtures, and air at increased pressures under the conditions of runaway electron generation. Voltage pulses of amplitude ∼90 and ∼250 kV were applied to a point-to-plane gap with a planar anode and a cathode of small curvature radius. Cathode spots appeared early in the discharge, within ∼200 ps of a corona discharge at high rate of rise of the voltage (∼5 × 1014 V/s) across centimeter point-to-plane gap spacing. The spark leader that bridged the point-to-plane gap propagated from the planar anode with cathode spots and a voltage pulse rise time of less than 1 ns. The discharge from diffuse clouds took the form of diffuse jets with increasing pulse repetition rate, thus achieving the accumulation effect in a repetitively pulsed discharge. Characteristic emission spectra are presented for spark diffuse and corona discharges.

Lasing from the domain of collision of ionisation waves produced due to electric field concentration at electrodes with a small radius of curvature

The characteristics of UV lasing in nitrogen and of diffusive discharge produced without an additional ionisation source were experimentally investigated in a nonuniform electric field formed by electrodes with different profiles. High-voltage nanosecond pulses were applied to the blade- and cylinder-shaped electrodes. It was determined that the gap breakdown at elevated pressure was caused by diffusive jets which propagate from the electrodes with a small radius of curvature. The electric field increasedin the intersection of counter-propagating jets, with the effect that the threshold of lasing in the C3Πu — B3Πg (λ = 337.1 nm) molecular nitrogen band was attained for low average electric fields (below 60 V cm-1 Torr-1) and at pressures of 760 Torr and above. With lowering the pressure from 760 to 20 Torr, the voltage of gap breakdown in the nonuniform electric field was observed to increase for a voltage pulse rise time of ∼300 ps and to decrease for a pulse rise timeof ∼2 ns.

On the influence of the voltage pulse rise time and cathode geometry on the generation of a supershort avalanche electron beam

The influence of the voltage pulse rise time on the amplitude of a runaway electron beam and X-ray generation in air and nitrogen under atmospheric pressure is studied experimentally and theoretically. Generalization of the whistle criterion for the case of a nonuniform field is suggested. It is shown that the maximal energy of beam electrons and the beam current amplitude grow when the voltage pulse rise time decreases. It is found that the amplitude of the runaway electron current reaches a maximum at a certain curvature of the cathode. The maximal energy of electrons increases when the radius of curvature of the cathode exceeds the value at which the beam current amplitude is the highest. If the field is nonuniform, its critical value at which many electrons run away is more than an order of magnitude lower than in the uniform field.

A high voltage pulsed power supply for capillary discharge waveguide applications

We present an all solid-state, high voltage pulsed power supply for inducing stable plasma formation (density ∼10(18) cm(-3)) in gas-filled capillary discharge waveguides. The pulser (pulse duration of 1 μs) is based on transistor switching and wound transmission line transformer technology. For a capillary of length 40 mm and diameter 265 μm and gas backing pressure of 100 mbar, a fast voltage pulse risetime of 95 ns initiates breakdown at 13 kV along the capillary. A peak current of ∼280 A indicates near complete ionization, and the r.m.s. temporal jitter in the current pulse is only 4 ns. Temporally stable plasma formation is crucial for deploying capillary waveguides as plasma channels in laser-plasma interaction experiments, such as the laser wakefield accelerator.

X-ray and runaway electron generation in repetitive pulsed discharges in atmospheric pressure air with a point-to-plane gap

In this paper, using two repetitive nanosecond generators, x-rays were detected in atmospheric air with a highly inhomogeneous electric field by a point-to- plane gap. The rise times of the generators were about 15 and 1 ns. The x-rays were directly measured by various dosimeters and a NaI scintillator with a photomultiplier tube. X-rays were detected in the continuous mode at pulse repetition frequency up to 1 kHz and a voltage pulse rise time of ∼15 ns. It is shown that the maximum x-ray intensity is attainable at different pulse repetition frequencies depending on the voltage pulse parameters and cathode design. In atmospheric pressure air the x-ray intensity is found to increase with increasing the pulse repetition frequency up to 1 kHz. It is confirmed that the maximum x-ray intensity is attained in a diffuse discharge in a point-to-plane gap.

Spectrum of fast electrons in a subnanosecond breakdown of air-filled diodes at atmospheric pressure

In this work, the spectra of electron beams produced in air-filled diodes at atmospheric pressure were studied for different cathode designs. The feasibility of correct reconstruction of the electron beam spectrum from an experimental dependence of its attenuation factor in foils of different thicknesses was demonstrated. The electron energy distributions were calculated on minimum a priori assumptions by regularization of an ill-posed problem—a Fredholm integral equation. The spectra of a subnanosecond electron beam generated in the gas gap during the voltage pulse rise time were reconstructed and analysed. A time-of-flight spectrometer study and reconstruction of the spectrum from the data on e-beam attenuation confirmed the fact that groups of electrons with two-three characteristic energies can be generated in gas-filled diodes. In experiments, electrons of energy greater than that corresponding to the nominal voltage amplitude across the gap were detected.

Characteristics of plasma immersion ion implantation with a nanosecond rise-time pulse: particle-in-cell simulations

Processes of plasma immersion ion implantation are analyszed numerically using a one-dimension-in-space and three-dimension-in-velocity particle-in-cell plus Monte Carlo collision (1D3V PIC–MCC) model. The behaviour of ions and electrons between the processed target and the source plasma is simulated after a nanosecond rise-time voltage pulse is applied to the target. The simulation results show that electron–neutral ionization collisions play a significant role in determining the magnitudes of the ion and electron densities when the pulse rise time is very short, and that the plasma density can be enhanced many times. The physical mechanism for this phenomenon is explained in terms of the formation of a reverse electric field inside the plasma chamber.

Harmonic Analysis of AlN Piezoelectric Mesa Structures

AbstractIn this work we report the displacement response of piezoelectric Aluminum Nitride (AlN) thin film MESA in an electrical circuit consisting of a circular MESA in series with a resistance subjected to time varying electrical loads. ANSYS was utilized for the simulation of 3D piezoelectric structures; using coupled field analysis to understand the electro-mechanical behavior of AlN thin film mesas. ANSYS applies finite element analysis (FEM) method to simulate the transient piezoelectric trends. Ringing and overshoot effects were observed in the thin simulation results on applying pulse voltages of varying frequencies to the circuit. The fast rise time of the voltage pulse could be exciting these effects. The effect of fast rising pulse voltages on the RC time constant of the circuit is still unclear at this point and needs to be further investigated.

X-ray radiation from the volume discharge in atmospheric-pressure air

X-ray radiation from the volume discharge in atmospheric-pressure air is studied under the conditions when the voltage pulse rise time varies from 0.5 to 100 ns and the open-circuit voltage amplitude of the generator varies from 20 to 750 kV. It is shown that a volume discharge from a needle-like cathode forms at a relatively wide voltage pulse (to ≈60 ns in this work). The volume character of the discharge is due to preionization by fast electrons, which arise when the electric field concentrates at the cathode and in the discharge gap. As the voltage pulse rise time grows, X-ray radiation comes largely from the discharge gap in accordance with previous experiments. Propagation of fast avalanche electrons in nitrogen subjected to a nonuniform unsteady electric field is simulated. It is demonstrated that the amount of hard X-ray photons grows not only with increasing voltage amplitude but also with shortening pulse rise time.

Effects of pulsed-excitation applied voltage rise time on argon metastable production efficiency in a high pressure dielectric barrier discharge

The authors have quantified the effect of pressure scaling on Ar metastable production efficiency in a dielectric barrier discharge with and without dielectric component losses. Estimates of the volume averaged deposited energy were performed for both short or long rise time voltage pulses, using the same total applied voltages of ∼10 and ∼150ns, respectively. The metastable production efficiencies of long-pulse discharge exhibit smaller decrease over the 100–500Torr pressure range, compared to those of the short-pulse one to the extent that the efficiency values and scaling for both cases are essentially the same within the experimental uncertainty.

Spectrum of fast electrons in a dense gas in the presence of a nonuniform pulsed field

The problems of gas preionization in discharges related to laser physics are considered. The propagation of fast electrons injected from the cathode in the presence of a nonuniform nonstationary field and the motion of multiplying electrons at the edge of the avalanche in the presence of a nonuniform nonstationary field are simulated. The effect of the voltage pulse steepness and the field nonuniformity on the mean propagation velocity of fast electrons and their energy distribution is demonstrated. At certain combinations of the voltage pulse rise time and amplitude and at a certain time interval, the center of gravity of the electron cloud can move in the opposite direction relative to the direction of force acting upon electrons. It is also demonstrated that the number of hard particles (and, hence, the hard component of the x-ray bremsstrahlung) increases with both an increase in the voltage amplitude and a decrease in the pulse rise time. For nonoptimal conditions of the picosecond voltage pulse, an assumption is formulated: an electron beam in gas is formed due to the electrons at the edge of the avalanche rather than the background multiplication wave approaching the anode.

Effect of insulating films on the current of an electron beam from gas-filled diodes exposed to voltage pulses with a nanosecond rise time

The parameters of subnanosecond electron beams generated in gas-filled diodes are studied. When the voltage pulse rise time is short (≈1 ns or less) and the electron beam is extracted from the diode through insulating films, the amplitude of the signal measured at the collector depends not on the electron beam current but on the electromagnetic radiation arising in the diode and the capacitive current from the collector. If the electron beam is extracted through thin metallic foils and fine metallic grids, the FWHM of the runaway electron pulsed beam is ≈0.1 ns and its amplitude reaches several hundreds of amperes.

Electron beam formation in a gas diode at high pressures

Electron beam formation in krypton, neon, helium, and nitrogen at elevated pressures are experimentally investigated. It is shown that, when the krypton, neon, and helium pressures are varied, respectively, from 70 to 760 Torr, from 150 to 760 Torr, and from 300 to 4560 Torr, runaway electrons are beamed at the instant the plasma in the discharge gap approaches the anode and the nonlocal criterion for electron runaway is fulfilled. The fast-electron simulation of discharge gap preionization is performed. The simulation data demonstrate that preionization in the discharge gap is provided if the voltage pulse rise time is shorter than a nanosecond under atmospheric pressure.

2-MV electrostatic quadrupole injector for heavy-ion fusion

High current and low emittance are principal requirements for heavy-ion injection into a linac driver for inertial fusion energy. An electrostatic quadrupole injector is capable of providing these high charge density and low emittance beams. We have modified the existing 2-MV injector to reduce beam emittance and to double the pulse length. We characterize the beam delivered by the modified injector to the High Current Transport Experiment and the effects of finite rise time of the extraction voltage pulse in the diode on the beam head. We demonstrate techniques for mitigating aberrations and reducing beam emittance growth in the injector.

Ultrashort electron beam and volume high-current discharge in air under the atmospheric pressure

Conditions are studied under which an electron beam and a volume discharge with a subnanosecond rise time of a voltage pulse are produced in air under atmospheric pressure. It is shown that the electron beam appears in a gas-filled diode at the front of the voltage pulse in ∼0.5 ns, has a half-intensity duration of ≤0.4 ns and an average electron energy of ∼0.6 of the voltage across the gas-filled diode, and terminates when the voltage across the gap reaches its maximum value. The electron beam with an average electron energy of 60 to 80 keV and a current amplitude of ≥70 A is obtained. It is assumed that the electron beam is formed from electrons produced in the gap due to gas ionization by fast electrons when the intensity of the field between the front of the expanding plasma cloud and the anode reaches its critical value. A nanosecond volume discharge with a specific power input of ≥400 MW/cm3, a density of the discharge current at the anode of up to 3 kA/cm2, and specific energy deposition of ∼1 J/cm3 over 3 to 5 ns is created.

The importance of bias pulse rise time for determining shallow implanted dose in plasma immersion ion implantation

The composition of the low-energy ions arising from the rise and fall time periods of the voltage pulse in plasma immersion ion implantation (PIII) are simulated by particle-in-cell (PIC) modeling. It is shown that more than 70% of the low-energy ions with an energy corresponding to less than half of the applied voltage come from the short rise time period. Although the fall time period is typically 30 times longer than the rise time, less than 25% of the low-energy ions originate from it. Based on the PIC results, the depth profile of the implanted ions is derived using the Monte-Carlo code SRIM2000 [J. F. Ziegler, The Stopping and Range of Ions in Solids (Pergamon, New York, 1985)]. The low-energy ions are found to be implanted to a much shallower depth than ions introduced during the fall time period the concentration profile which decays more sharply into the bulk. These results indicate that the most effective way to reduce or increase the surface concentration is by adjusting the rise time of the PIII voltage pulse. This will require a power supply capable of fast rise times and good matching between power supply and load.

Numerical simulation of plasma implanted nitrogen depth profiles in iron

Plasma immersion ion implantation (PIII) is a relatively complex process. Utilizing plasma and TRIM simulation, plasma implanted nitrogen depth profiles in iron are simulated in this work. Many factors such as the high voltage pulse rise time, voltage amplitude, pulse duration, plasma composition, etc. have a critical influence on this depth profiles. Our results confirm the broader distribution as well as shift of the implant peak toward the surface. Compared to the pulse duration and plasma composition, the rise time of the high voltage pulse has a more predominant effect on the shape of the profile. At higher implantation voltage, the nitrogen profile resembles that of multiple energy implantation in the beam-line mode. From this perspective, broadening of the ion energy spectrum in PIII is favorable since a single process can achieve the results of multiple energy ion implantation. This is particularly useful for processes such as shallow junction formation in microelectronics.