Sub-nanosecond Voltage Pulses Research Articles

Design and experiment of broadband electric field sensor for high-power sub-nanosecond pulse measurements

This paper briefly introduces the structure and working principle of the electric field sensor. And a conductive electric field sensor for measuring sub-nanosecond voltage pulse is designed. The sensor consists of coaxial transition section and integrated electric field probe. N-type connector and SMA connector are selected for input/direct output port and coupling output port respectively. The equivalent antenna area of electric field sensor measured by vector network analyzer is about 0.035cm2, and the 3dB bandwidth is more than 5GHz. The results show that the sensor can accurately measure the time-domain voltage pulse produced by the sub-nanosecond solid-state sources.

Generation and routing of nanoscale droplet solitons without compensation of magnetic damping

A magnetic droplet soliton is a localized dynamic spin state which can serve as a nanoscale information carrier and nonlinear oscillator. The present opinion is that the formation of droplet solitons requires the compensation of magnetic damping by a torque created by a spin-polarized electric current or pure spin current. Here, we demonstrate theoretically that nanoscale droplet solitons can be generated and routed in ferromagnetic nanostructures with voltage-controlled magnetic anisotropy in the presence of uncompensated magnetic damping. Performing micromagnetic simulations for the MgO/Fe/MgO trilayer with almost perpendicular-to-plane magnetization, we reveal the formation of the droplet soliton under a nanoscale gate electrode subjected to a subnanosecond voltage pulse. The soliton lives up to 50 ns at room temperature and can propagate over micrometer distances in a ferromagnetic waveguide due to nonzero gradient of the demagnetizing field. Furthermore, we show that electrical routing of the soliton to different outputs of a spintronic device can be realized with the aid of an additional semiconducting nanostripe electrode creating controllable gradient of the perpendicular magnetic anisotropy.

Two‐dimensional particle‐in‐cell/Monte Carlo simulations of streamer formation and propagation in catalyst pores in a surface dielectric barrier discharge

AbstractPlasma catalysis is attracting great interest due to its synergistic combination of catalytic and plasma reactor processes. To provide possible controlling methods to this tunability, two‐dimensional particle‐in‐cell/Monte Carlo simulations are applied to investigate the propagation mechanisms of plasma streamers in the porous catalyst in a surface dielectric barrier discharge. Dry air at atmospheric pressure is investigated under a subnanosecond voltage pulse. The results show that the presence of the catalyst pores could enhance the steamer intensity and control the direction of the streamers, yielding highly concentrated reactive species inside catalyst pores. The streamer propagation speed is enhanced by increasing the strength of cathode voltage. These high‐density plasma streamers with controllable direction could benefit many applications in plasma‐enhanced catalysis.

Emission of xenon in the spectral range of 120 – 800 nm upon excitation by diffuse and spark discharges

Xenon emission in the spectral range of 120 – 800 nm upon excitation by subnanosecond voltage pulses is investigated. Excitation is performed using diffuse and spark discharges in an inhomogeneous electric field at a xenon pressure ranging from 0.3 to 3 atm. It is shown that xenon excitation by a series of successive 0.7-ns voltage pulses with a pause of 30 ns leads to a decrease in the second-continuum radiation intensity by the second and subsequent voltage pulses and an increase in the first-pulse afterglow intensity. It is confirmed that in the case of a pulsed diffuse discharge, the second continuum of xenon dimers, which is used to generate laser and spontaneous radiation in the VUV spectral region, makes the largest contribution to the radiation energy. Broadband radiation in the visible range (λ > 400 nm) is found to occur when the discharge is constricted. The obtained results indicate that the influence of the dynamic displacement current on the pin-diode caused a measurement error in the papers by V.I. Baryshnikov et al., who did not record the second-continuum radiation from xenon excited by a short homogeneous discharge.

Performance of microchannel plate based detectors for

We present the results of Monte Carlo simulations of the microchannel plate (MCP) response to x rays in the 250eV to 25 keV energy range as a function of both x-ray energy and impact angle and their comparisons with the experimental results from the X8A beamline at the National Synchrotron Light Source at Brookhaven National Laboratory. Incoming x rays interact with the lead glass of the microchannel plate, producing photoelectrons. Transport of the photoelectrons is neglected in this model, and it is assumed that photoelectrons deposit all their energy at the point they are created. This deposition leads to the generation of many secondary electrons, some fraction of which diffuse to the MCP pore surface where they can initiate secondary electron cascades in the pore under an external voltage bias. X-ray penetration through multiple MCP pore walls is increasingly important above 5 keV, and the effect of this penetration on MCP performance is studied. In agreement with past measurements, we find that the dependence of MCP sensitivity with angle relative to the pore bias changes from a cotangent dependence to angular independence and then proceeds to a secant dependence as the x-ray energy increases. We also find that with the increasing x-ray energy, the MCP gain sensitivity as a function of bias voltage decreases. The simulations also demonstrate that for x rays incident normal to the MCP surface, spatial resolution shows little dependence on the x-ray energy but degrades with the increasing x-ray energy as the angle of incidence relative to the surface normal increases. This agrees with experimental measurements. Simulation studies have also been completed for MCPs gated with a subnanosecond voltage pulse. We find that the optical gate profile width increases as the x-ray energy is increased above 5 keV, a consequence of increased x-ray penetration at energies >5 keV. Simulations of the pulsed dynamic range show that the dynamic range varies between ∼100 and 1000 depending on x-ray energy and peak voltage.

Numerical Study of the Feasibility of Runaway Electron Generation in an Emerging Cathode Layer of a Self-Sustained High-Pressure Space Discharge

The formation of the cathode layer of a self-sustained high-pressure space discharge with preliminary ionization of a gas medium, excited by nano- and subnanosecond voltage pulses, is calculated. It is shown that, at pressures of ~1 atm, at the final stage of cathode layer formation, conditions for runaway electron generation are created. Runaway electrons from the electric field amplification region in front of the leading edge of a plasma (streamer) channel, originating from the top of the cathode micronib, is considered. It is shown that, at pressures of ~10 atm, conditions are created for the runaway of electrons immediately after their emission from the top of the micronib in its amplification zone; the runaway electrons thus obtained, in turn, can create preliminary ionization of the gas medium and ensure the formation of the initial phase of space discharge in systems without illumination.

Nanosecond resistive switching in Ag/AgI/PtIr nanojunctions.

Nanometer-scale resistive switching devices operated in the metallic conductance regime offer ultimately scalable and widely reconfigurable hardware elements for novel in-memory and neuromorphic computing architectures. Moreover, they exhibit high operation speed at low power arising from the ease of the electric-field-driven redistribution of only a small amount of highly mobile ionic species upon resistive switching. We investigate the memristive behavior of a so-far less explored representative of this class, the Ag/AgI material system in a point contact arrangement established by the conducting PtIr tip of a scanning probe microscope. We demonstrate stable resistive switching duty cycles and investigate the dynamical aspects of non-volatile operation in detail. The high-speed switching capabilities are explored by a custom-designed microwave setup that enables time-resolved studies of subsequent set and reset transitions upon biasing the Ag/AgI/PtIr nanojunctions with sub-nanosecond voltage pulses. Our results demonstrate the potential of Ag-based filamentary memristive nanodevices to serve as the hardware elements in high-speed neuromorphic circuits.

Численное исследование возможности генерации убегающих электронов в формирующемся катодном слое самостоятельного объемного разряда высокого давления

Calculations of the formation of the cathode layer of an self-sustained high-pressure volume discharge with pre-ionization of the gas medium excited by nano-and subnanosecond voltage pulses are carried out. It is shown that at pressures of ~ 1 atm at the final stage of the cathode layer formation, conditions for the generation of escaping electrons arise. We also considered the transition of electrons into runaway mode from the area of electric field amplification in front of the plasma (streamer) channel, which originates from the top of the micro-spike on the cathode. It is shown that at pressures of ~ 10 atm, electrons can transfer into runaway mode immediately after emission from the top of micro-spike in amplified electric field. Thus obtained runaway electrons can create pre-ionization of the gaseous medium and provide the formation of the initial phase of the discharge in volume form in the system without external pre-ionization.

Thermally Induced Precession-Orbit Transition of Magnetization in Voltage-Driven Magnetization Switching

Dynamic switching of magnetization driven by subnanosecond voltage pulses would be a central technology for realizing ultralow-power magnetic random-access memory. For practical applications, however, there is a strong demand to reduce the write-error rate. This study shows that transitions of magnetization between different precession orbits, as induced by thermal fluctuations, play a dominant role in the probability of write error. The transitions can be avoided by choosing a proper width for the write voltage pulse. These findings will promote the development of voltage-driven spintronic devices.

Study of the Formation Time of a Self-Sustained Subnanosecond Discharge at High and Ultrahigh Gas Pressures

The formation times of self-sustained subnanosecond discharges in nitrogen at pressures of 1‒40 atm and in hydrogen at pressures of 1–60 atm are analyzed in terms of the avalanche model. In experiments, a subnanosecond voltage pulse with an amplitude of 102 ± 2 kV was applied to a 0.5-mm-long discharge gap with a uniformly distributed electric field (the curvature radii of both the cathode and anode ends were 1 cm). The rise time of the voltage pulse from 0.1 to 0.9 of its amplitude value was about 250 ps. Breakdown occurred at the leading edge of the pulse. The discharge formation time was measured at different gas pressures with a step of 5–10 atm. Analysis of the experimental results shows that, in nitrogen at pressures of 10–40 atm and in hydrogen at pressures of 20–50 atm, breakdown occurs earlier than the electron avalanche reaches its critical length and that the critical avalanche length lies in the range of (2–8) × 10–2 mm, which is one order of magnitude shorter than the discharge gap length. This means that the avalanche–streamer model is inapplicable in this case. The fast formation of a conducting channel under these conditions can be explained by ionization of gas by runaway electrons. In this case, the conducting column develops as a result of simultaneous development of a large number of electron avalanches in the gas volume. An increase in the hydrogen pressure from 50 to 60 atm leads to an abrupt increase in the discharge formation time by about 50%. As a result, the growth time of the electron avalanche to its critical length becomes shorter than the discharge formation time. In this case, the electrons cease to pass into the runaway regime and the discharge is initiated from the cathode due to field emission from microinhomogeneities on its surface. Under these conditions, the discharge formation time is well described by the avalanche–streamer model.

On the parameters of runaway electron beams and on electrons with an “anomalous” energy at a subnanosecond breakdown of gases at atmospheric pressure

The generation of runaway electron beams in gases at atmospheric pressure has been studied with a real picosecond accuracy. Their main parameters have been determined. It has been found that three groups of electrons can be separated at a subnanosecond voltage pulse in a runaway electron beam generated in air at atmospheric pressure. It has been proven that the duration of a beam pulse in air at atmospheric pressure behind an anode foil is ~100 ps.

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.

Measurements of high voltage pulses with subnanosecond rise time

The paper deals with the application features of capacitive probes for subnanosecond voltage pulse measurements. The relation for the amplitude of distortions determined by the finite electrical length of a capacitive divider was obtained. This relation could serve for quantitative estimation of capacitive divider suitability. Probes of various designs were used for recording the high voltage pulses with subnanosecond voltage changes. The pulse shapes with voltage change durations of 0.2 - 20 ns from different voltage probes were compared. It was shown that the use of capacitive divider with high- and low-voltage arms filled with the same material is more appropriate. This divider provides the same voltage ratio for voltage changes of durations from tens to fractions of nanoseconds.

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.

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.

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.

Simulation and solving the descriptive equations on the voltage breakdown in ultra-quick circuit breakers

This paper presents descriptive equations on the voltage breakdown in ultra-quick circuit breakers (UQCB). In this paper, main breakdown characteristics of UQCB\'s are presented. Gaseous breakdown in the sub-nanosecond regime is of interest for fast pulsed power switching, short pulse electromagnetics, and for plasma limiters to protect devices from high power microwave radiation. In order to study pulsed gas breakdown initiation dynamics, a sub-nanosecond voltage pulse is simulated by Electro-Magnetic Transient Program (EMTP). Keywords: Ultra Quick circuit breakers, Voltage breakdown, Gaseous breakdown, Transient recovery voltage.

Monte Carlo simulations of microchannel plate detectors. II. Pulsed voltage results

This paper is the second part of a continuing study of straight-channel microchannel plate (MCP)-based x-ray detectors. Such detectors are a useful diagnostic tool for two-dimensional, time-resolved imaging and time-resolved x-ray spectroscopy. To interpret the data from such detectors, it is critical to develop a better understanding of the behavior of MCPs biased with subnanosecond voltage pulses. The subject of this paper is a Monte Carlo computer code that simulates the electron cascade in a MCP channel under an arbitrary pulsed voltage, particularly those pulses with widths comparable to the transit time of the electron cascade in the MCP under DC voltage bias. We use this code to study the gain as a function of time (also called the gate profile or optical gate) for various voltage pulse shapes, including pulses measured along the MCP. In addition, experimental data of MCP behavior in pulsed mode are obtained with a short-pulse UV laser. Comparisons between the simulations and experimental data show excellent agreement for both the gate profile and the peak relative sensitivity along the MCP strips. We report that the dependence of relative gain on peak voltage is larger in pulsed mode when the width of the high-voltage waveform is smaller than the transit time of cascading electrons in the MCP.

Miniature UV lamp excited by subnanosecond voltage pulses

Energy, time, and spectral characteristics of emission of the second positive system of N2 molecules in gaseous nitrogen, Ar — N2 mixture, and air are investigated. An FPG-10 generator with voltage pulse FWHM of 200 and 400 ps and matched-load amplitudes of 14 and 6 kV, respectively, is used to excite gases. It is shown that excitation can be performed in two regimes using this generator. In the first regime a diffuse discharge is formed at atmospheric pressure, which opens ways to design miniature nanosecond UV lamps. A diffuse discharge is formed due to the generation of runaway electrons, with the aid of electrodes having a small radius of curvature and voltage pulses with a sharp leading edge. In the second regime an elevated average radiation power is obtained under excitation by a barrier discharge. However, the operating pressure is lower in this case, and the sizes of the emitting region and the UV pulse width significantly increase.

The RADAN series of compact pulsed power Generators and their applications

This paper presents results of development of a compact pulsed power high-voltage generators and high-current electron accelerators of the RADAN series. The basic high-voltage units of RADAN instruments are built around coaxial pulsed forming lines and efficient charging device represented by a Tesla transformer. The fields of applications in science and in practice are rather wide and include formation of nanosecond and subnanosecond voltage and ultrawideband RF pulses, high-power microwave generation, X-ray radiography, radiation physics, chemistry, and biology. The designed technique provided achievements of outstanding specific parameters of dense e-beams, microwaves, and ultrawideband pulses.