Pulse Rise Time Research Articles

Effects of pulse rise time and pulse width on discharge mode transition of SDBD plasma under repetitive pulses

Abstract Affected by environmental states and power supply parameters, the discharge mode of surface dielectric barrier discharge plasma may gradually transfer from O3 mode to NOx mode, resulting in various gas-phase species for different applications. Despite the intensive study of attempts to control this discharge mode transition by changing discharge conditions and power excitations in recent years, the effects of the pulse rise time and the pulse width on the discharge mode transition have not been discussed. In the present study, a surface dielectric barrier discharge was excited by repetitive pulses with different pulse rise times or pulse widths, and the time-varying concentrations of key long-lived species (O3 and NO2) were quantified. The results demonstrated that it was possible to modulate the discharge mode by adjusting pulse rise time/pulse width. The quenching of O3 was observed to occur at a faster rate and the mode transition was noted to occur at an earlier point in time as the pulse rise time decreased from 225 ns to 125 ns and the pulse width increased from 0.5 μs to 4 μs. The employment of a zero-dimensional model for the analysis of plasma chemical kinetics revealed that the reduction in pulse rise time and the prolongation of pulse width resulted in an increase in the mean vibrational energy of N2(v) and a more rapid electrode temperature rise caused by plasma heating. The former enhanced the generation of NO, while the latter accelerated the thermal decomposition of O3, thereby promoting the speed of mode transition.

Instrumentation techniques for the measurement of gunfire (Part 3)

This paper is the third in a series concerning near-field measurement of sound pressure from small arms gunfire. It has been long established that exposure to gunfire events can lead to permanent threshold shift for an unprotected shooter. Close to a shooter's ear, the peak sound pressure level from a rifle or pistol can be 155-to-160 decibels with a pulse rise time on the order of ten microseconds. The U.S. Department of Defense has considered two approaches for assessing exposure limits from small arms gunfire - one involves the unweighted peak sound pressure and the other a series of A-weighted sound exposure events integrated to obtain an equivalent eight-hour dose. This dose is then compared to hearing damage risk criteria established for continuous noise signals. The first approach places great demands on the measurement system since the necessary bandwidth extends well into the ultrasonic range, thereby requiring fast slewing from the amplifiers combined with high sampling rates from the digitizer. The second approach requires the A-weighting filter to have specified time and frequency domain properties in the ultrasonic region. The paper discusses some laboratory experiments using actual gunfire signals to simulate the outcome from both approaches.

Simulation of the pulsed streamer discharge in water considering the effect of hydrostatic pressure

Streamer discharge is a very complex multi-scale and multi-physics coupling process, and there is no accurate model that can describe its development. In this paper, a two-dimensional axisymmetric fluid model is established in COMSOL to simulate and study the effects of the applied voltage amplitude, the discharge gap distance, the rising edge of pulse voltage, and hydrostatic pressure on the development of the positive streamer discharge at a needle-plate electrode in water under a nanosecond pulse voltage. The results show that increasing the voltage amplitude, decreasing the pulse rise time, and narrowing the discharge gap all increase the electric field strength of the streamer, thereby affecting the electron density of the plasma channel, among which changing the discharge gap has the greatest effect on the electron density. And under the gap of 3 mm, the peak electron density can reach 3.76 × 1023 m−3; if the discharge gap is narrowed to 1 mm, the peak electron density is reduced to 1.20 × 1023 m−3. In addition, hydrostatic pressure and water molecule spacing are closely linked. Increasing the hydrostatic pressure decreases the electric field strength and the peak electron density in the plasma channel, and its effect on the peak electron density saturates with increasing hydrostatic pressure.

Considerations for Exploring Nanosecond Pulsed Electric Fields (nsPEFs) for Treatments of Cancer, Benign Skin Diseases, Atrial Fibrillation, and for New Mechanistic Understandings

Pulsed power includes acquiring electrical energy, compressing it, and releasing it in instantaneous bursts that are low in energy but very high in power. When the pulse duration is near the plasma membrane charging time constant, which is the time during which the cell interior is exposed to the applied pulsed electric field, it affects intracellular structures and functions. The technology is called nanosecond Pulsed Electric Fields (nsPEFs), nanosecond electric pulses (nsEP), or Nanopulse Stimulation (NPSTM) according to Pulse Biosciences, Inc., a company taking the technology to the market. Initial studies showed the elimination of tumor cells in vitro by apoptosis, and other regulated cell death mechanisms, elimination of rodent and canine osteosarcoma, and a basal cell carcinoma clinical trial. In the rat liver and mouse breast cancers, tumor-free animals were in situ vaccinated (ISV), preventing the recurrence of the treated cancers. The technology has also focused on treating benign skin diseases, with some advantages over cryoablation. More recently, the same technology called nanosecond pulsed-field ablation (nsPFA) has been used to treat cardiac arrhythmias like Atrial Fabulation (AFib) with catheters in humans. In pre-clinical studies and now in humans, this technology is showing advantages over radiofrequency ablation and cryoablation. On a new mechanistic landscape, nonlethal nsPEFs modulation of electron transport in the plasma membrane and the mitochondria show potential for controlling redox homeostasis and metabolism. Furthermore, different nsPEF waveforms have different effects on cells; waveforms can differ by pulse duration, rise time, electric field, and/or post-pulse features. So, for nsPEFs, there is a lethal side used for ablation as with NPS and nsPFA and a more recently recognized nonlethal side indicating new possibilities to differentially modify cell physiology depending on the different nsPEF waveforms.

Thermo-diffusion of excited photothermal semiconductor under laser pulse and ramp heating with acoustic pressure

The goal of this work is to provide a novel mathematical model that explains how certain physical variables propagate (acoustic-thermal-mechanical diffusive) as waves in a photoexcited non-Gaussian laser pulse semiconductor medium. Under the impact of acoustic pressure, the isotropic and homogeneous semiconductor medium is discussed concerning the fundamental equations according to charge carrier recombination processes with optoelectronic properties. Given the impact that relaxation times have on the governing equations. Laplace transforms were utilized in a one-dimensional (1D) context to examine essential non-dimensional properties such as displacement, stress components, carrier density, temperature, and acoustic pressure in order to mathematically answer the required problem. By imposing specific initial and boundary conditions, inverse Laplace transformations were employed to generate precise solutions for the numerical modeling of different physical quantities depicted graphically. The graphical representation of wave propagation data was followed by a theoretical analysis and interpretation, emphasizing the influence of other factors (such as heat rise time, relaxation times, and laser pulse effects) on the observed occurrences.

Analytical and numerical models to predict the shape of incident pulse in split-Hopkinson bar experiments

In typical split-Hopkinson pressure bar experiments (SHPB), the striker bar impacts the incident bar via discs made from soft materials such as copper. These discs, also called pulse shapers, are used (i) to eliminate the high frequency components of the incident pulse, (ii) to obtain a finite rise time of the incident pulse and (iii) to obtain a constant strain rate. Although these pulse shapers have been used for over decades in SHPB experiments, no analytical solutions or simple models are available that can predict the incident pulse as a function of the striker velocity, pulse shaper geometry and material parameters. Assuming that the pulse shaper is a rigid-linearly hardening material, we derive the analytical solution for the incident pulse when the rise time of the incident pulse is less than twice the time taken for a longitudinal wave to travel along the length of the striker. For larger rise times, we additionally assume that the striker is rigid to obtain a simple numerical model to predict the incident pulse in the presence of a pulse shaper. Both these models are validated against numerical simulations and experiments to demonstrate their accuracy.

Electric energy output characteristics of polyvinylidene fluoride piezoelectric transducer under pulse stress: A simplified model

Because of its excellent performance, polyvinylidene fluoride (PVDF) transducers are commonly used to convert pulse kinetic energy into electrical energy. To quantify the relationship between the transducer's input pulse stress and output electrical energy, this study established a voltage output model by simplifying the pulse stress into a triangular pulse. Then, the model's reliability was verified through three experiments, and the causes of model deviations were determined. Subsequently, the influence of the transducer (area A and piezoelectric constant K), pulse stress (pulse rise time t1 and loading rate F1), and circuit (load resistance Rm and PVDF capacitance CP) on energy conversion were analyzed with the model. Results show A, K, and F1 are directly proportional to the maximum output voltage Vmax. As Rm increases, Vmax increases and gradually approaches the limit value, AKF1t1/CP. When the peak stress remains constant, the influence of t1 on Vmax is opposite to that of Rm. When CP is larger than t1/10Rm, reducing CP leads to Vmax increases, and the increasing rate is maximized as CP approaches t1/2Rm. This study clarifies the influence of key parameters in the harvester on its energy output characteristics, which is helpful for its optimizing design in different applications.

High-voltage pulse generator for time-of-flight mass spectrometry in electrospray thrusters.

Electrospray thrusters exhibit diverse operational modes based on the nature of ejected particles. Time-of-flight mass spectrometry is frequently employed to analyze the composition of the plume. This study introduces a novel converter-based bipolar high-voltage pulse generator aimed at producing synchronized bipolar high-voltage pulses with controllable voltage levels and frequencies, specifically tailored for the study of electrospray thrusters. The proposed topology generates bipolar high-voltage rails from a low-voltage power source through the forward-flyback with Cockcroft-Walton voltage multiplier topology. Subsequently, fast high-voltage MOSFETs are employed to generate high-voltage pulses. This paper outlines the operational principles and design methodologies of the pulse generator. Experimental verification corroborates its operational principles and functionalities, revealing that the pulse rise and fall times consistently remain below 30ns, while the voltage can be tuned within the range of 300-1000V. An electrospray thruster was employed to conduct a thorough and practical validation of the high-voltage pulse generator. This included generating time-of-flight curves and mass spectra of the plume, resulting in precise differentiation of all particles present.

Design and characterization of a nano‐pulsed atmospheric pressure plasma jet for biomedical applications

AbstractPlasma jets, crucial atmospheric pressure sources in biomedical applications, generate reactive species in liquids, with electrical fields playing a significant role, as variations in pulse rise times and durations in dielectric barrier discharges yield diverse effects. This study presents a novel nanosecond pulse plasma jet. Here, investigations with phosphate‐buffered saline and Ringer's saline elucidate critical parameters influencing species generation, such as treatment time and gas flow rate. Results showed increasing concentrations of H2O2 and NO2− over time, with NO2− degrading faster in Ringer's saline due to acidification. The nanosecond pulse jet exhibits superior energy efficiency than conventional jets, laying the groundwork for optimizing species generation and studying electrical field effects in future biological works.

Perceptually salient differences in a species recognition cue do not promote auditory streaming in eastern grey treefrogs (Hyla versicolor).

Auditory streaming underlies a receiver's ability to organize complex mixtures of auditory input into distinct perceptual "streams" that represent different sound sources in the environment. During auditory streaming, sounds produced by the same source are integrated through time into a single, coherent auditory stream that is perceptually segregated from other concurrent sounds. Based on human psychoacoustic studies, one hypothesis regarding auditory streaming is that any sufficiently salient perceptual difference may lead to stream segregation. Here, we used the eastern grey treefrog, Hyla versicolor, to test this hypothesis in the context of vocal communication in a non-human animal. In this system, females choose their mate based on perceiving species-specific features of a male's pulsatile advertisement calls in social environments (choruses) characterized by mixtures of overlapping vocalizations. We employed an experimental paradigm from human psychoacoustics to design interleaved pulsatile sequences (ABAB…) that mimicked key features of the species' advertisement call, and in which alternating pulses differed in pulse rise time, which is a robust species recognition cue in eastern grey treefrogs. Using phonotaxis assays, we found no evidence that perceptually salient differences in pulse rise time promoted the segregation of interleaved pulse sequences into distinct auditory streams. These results do not support the hypothesis that any perceptually salient acoustic difference can be exploited as a cue for stream segregation in all species. We discuss these findings in the context of cues used for species recognition and auditory streaming.

Radiatively cooled magnetic reconnection experiments driven by pulsed power

We present evidence for strong radiative cooling in a pulsed-power-driven magnetic reconnection experiment. Two aluminum exploding wire arrays, driven by a 20 MA peak current, 300 ns rise time pulse from the Z machine (Sandia National Laboratories), generate strongly driven plasma flows (MA≈7) with anti-parallel magnetic fields, which form a reconnection layer (SL≈120) at the mid-plane. The net cooling rate far exceeds the Alfvénic transit rate (τcool−1/τA−1≫1), leading to strong cooling of the reconnection layer. We determine the advected magnetic field and flow velocity using inductive probes positioned in the inflow to the layer, and inflow ion density and temperature from analysis of visible emission spectroscopy. A sharp decrease in x-ray emission from the reconnection layer, measured using filtered diodes and time-gated x-ray imaging, provides evidence for strong cooling of the reconnection layer after its initial formation. X-ray images also show localized hotspots, regions of strong x-ray emission, with velocities comparable to the expected outflow velocity from the reconnection layer. These hotspots are consistent with plasmoids observed in 3D radiative resistive magnetohydrodynamic simulations of the experiment. X-ray spectroscopy further indicates that the hotspots have a temperature (170 eV) much higher than the bulk layer (≤75 eV) and inflow temperatures (about 2 eV) and that these hotspots generate the majority of the high-energy (>1 keV) emission.

Effectiveness of Noble Gas Addition for Plasma Synthesis of Ammonia in a Dielectric Barrier Discharge Reactor

Non-thermal plasma driven ammonia synthesis has great potential for future industrial applications due to its low theoretical energy requirements. To achieve technological advancement and environmental sustainability, it is crucial to boost the energy yield in plasma-assisted ammonia synthesis. Therefore, optimizing energy transfer and utilization are key strategies for enhancing energy efficiency. In this study, dielectric barrier discharge driven by a nanosecond pulsed power supply is used to enhance plasma-assisted ammonia synthesis by controlling the energy transfer through the addition of noble gases. It was found that the addition of noble gases changed the plasma characteristics, significantly improved the uniformity of the discharge, and achieved a high energy yield for ammonia synthesis. The effects of additive amounts of argon (Ar) and helium (He), as well as the pulse parameters including the pulse voltage, pulse repetition frequency, pulse width, and pulse rise time on the energy yield of ammonia synthesis are discussed. The inclusion of noble gases expanded the pathway for gas-phase reactions, with the active components of critical reactions examined through optical emission spectra. This analysis revealed an increased presence of both N2+ and N2* particles in the reaction’s rate-limiting step, attributed to the addition of noble gases. Finally, a zero-dimensional (0D) plasma chemical kinetic model was established to investigate the influence of Ar addition on the reaction mechanism of ammonia synthesis.

Design and investigation of a capacitance-coupling pre-ionized sharpening switch.

The sharpening switch is one of the most important elements in the trigger generator, which is used to sharpen the front of the trigger pulse. The breakdown performance of the sharpening switch has an important influence on the output and stability of the trigger generator. In this paper, a novel 200kV capacitance-coupling pre-ionized sharpening switch, which can realize pre-ionization by dividing voltage through its own structural capacitances, is proposed and investigated. In order to obtain the optimal parameters of the pre-ionized sharpening switch, the influences of the electrode structure, electrode material, main gap distance, and pre-ionized gap distance on the breakdown performance are studied experimentally. The experimental results show that the electrode structure with a circular knife-edged cathode and a plate-shaped anode has the smallest breakdown jitter, followed by the needle-plate structure and the tapered ball-head structure. The stainless steel electrode has the smallest jitter, followed by graphite, aluminum, and brass electrodes. When the gap distances of the main gap and the pre-ionized gap are 13 and 1.5mm, respectively, the breakdown stability of the pre-ionized sharpening switch is the best. Under an input voltage pulse with a rise time of about one microsecond, the jitter of the capacitance-coupling pre-ionized sharpening switch with the optimal parameters is 6.08ns, which is about 0.6% of the rise time of the input pulse. The jitter decreases by 44.5% compared to the switch without pre-ionization. The rise time of the output pulse is sharpened to 17ns, corresponding to a voltage rise rate of more than 11 kV/ns.

Pulse area compensation approach for ballistic deficits correction in perovskite CsPbBr3 semiconductor detector

Halide perovskite CsPbBr3 semiconductor has exhibited extraordinary performance on ionizing radiation detection at room temperature in the light of excellent photoelectric properties. However, signals from the CsPbBr3 planar detector usually comprises the long rising edge due to its low hole carrier mobility, subsequently leading to severe ballistic deficits in pulse amplitudes (over 10 %) when the shaping time is inferior to rise time. To overcome this issue, the integrated pulse area approach is proposed and implemented herein to compensate the amplitudes underestimation of pulses particularly with varied rise times. It was verified that the pulse area extracted by this approach was insensitive to the rise time (when varying from 1 to 130 μs) while manifesting the relative variance below 1.49 × 10−5. Accordingly, the bivariate distribution between the integrated pulse area and rise time regarded as unaffected by ballistic deficits was finally accomplished which reflected the actual depth of individual event interactions. The approach is computationally feasible in eliminating the ballistic deficit, and is anticipated to foster the deployment of perovskite detector in radiation detection.

Pulse-controlled qubit in semiconductor double quantum dots

We present a numerically-optimized multipulse framework for the quantum control of a single-electron double quantum dot qubit. Our framework defines a set of pulse sequences, necessary for the manipulation of the ideal qubit basis, that avoids errors associated with excitations outside the computational subspace. A novel control scheme manipulates the qubit adiabatically, while also retaining high speed and ability to perform a general single-qubit rotation. This basis generates spatially localized logical qubit states, making readout straightforward. We consider experimentally realistic semiconductor qubits with finite pulse rise and fall times and determine the fastest pulse sequence yielding the highest fidelity. We show that our protocol leads to improved control of a qubit. We present simulations of a double quantum dot in a semiconductor device to visualize and verify our protocol. These results can be generalized to other physical systems since they depend only on pulse rise and fall times and the energy gap between the two lowest eigenstates.

Backward fast electrons supported by ionization wave passing through the grid cathode

In this paper, the effect of appearance of fast electrons behind the grid cathode in the direction reverse to the anode is studied computationally. Fast electrons are observed within 0.5 ns after application of a short voltage pulse. The results obtained confirm the possibility of generation of backward fast electrons (some of them are in a runaway mode) and explain the main trends of this process. It is shown that backward fast electrons are supported by the ionization wave (IW). The IW evolution proceeds via two phases. During the first phase, first fast electrons are observed moving toward the anode. Then, multiple individual IWs starting from each individual cathode wire are formed in the anode–cathode gap. The duration of this stage is 0.3 ns and corresponds to the pulse rise time. At the second phase, the separate individual IWs merge in a single flat ionization wave. The IW penetrates through the cathode wires and propagates in the direction reverse to the anode. The preferred direction of fast electrons propagation also reverses. Now, the trajectories of fast electrons are mainly directed away from the anode. The duration of the recorded flux of fast electrons is of the order of a few picoseconds. This time interval correlates with the available experimental data.

Underwater microsecond timescale electrical explosions of aluminum and copper foils

We present results on underwater electrical explosions of thin aluminum and copper foils using a generator delivering ∼200 kA current amplitude, ∼0.9 μs rise time pulses. Time-resolved shadow imaging displays the generation of a strong planar shock wave in water in the vicinity of the exploding foil. Using time-resolved spectroscopy, aluminum oxide (AlO) absorption bands were observed in a Planckian-like spectrum, indicating that aluminum combustion starts when aluminum vaporizes. It is also shown that the strongest shock wave is obtained for the largest linear energy deposition rate to the foil.

Temperature dependence of the electron-drift anisotropy and implications for the electron-drift model

The electron drift in germanium detectors is modeled making many assumptions. Confronted with data, these assumptions have to be revisited. The temperature dependence of the drift of electrons was studied in detail for an n-type segmented point-contact germanium detector. The detector was mounted in a temperature controlled, electrically cooled cryostat. Surface events were induced with collimated 81 keV photons from a 133Ba source. A detailed analysis of the rise time of pulses collected in surface scans, performed at different temperatures, is presented. The longitudinal anisotropy of the electron drift decreases with rising temperature. A new approach, making use of designated rise-time windows determined by simulations using SolidStateDetectors.jl, was used to isolate the longitudinal drift of electrons along different axes to quantify this observation. The measured temperature dependence of the longitudinal drift velocities combined with the standard electron-drift model as widely used in relevant simulation packages results in unphysical predictions. A modification of the electron-drift model based on assuming phonons to be the dominating scattering centers for electrons is motivated and described. The results of a first implementation of the modified model in SolidStateDetectors.jl are shown. They describe the temperature dependence of the data reasonably well. A general review of the model and the standard input values for mobilities is suggested.

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.

Ultra-Low Intensity Post-Pulse Affects Cellular Responses Caused by Nanosecond Pulsed Electric Fields.

High-intensity nanosecond pulse electric fields (nsPEF) can preferentially induce various effects, most notably regulated cell death and tumor elimination. These effects have almost exclusively been shown to be associated with nsPEF waveforms defined by pulse duration, rise time, amplitude (electric field), and pulse number. Other factors, such as low-intensity post-pulse waveform, have been completely overlooked. In this study, we show that post-pulse waveforms can alter the cell responses produced by the primary pulse waveform and can even elicit unique cellular responses, despite the primary pulse waveform being nearly identical. We employed two commonly used pulse generator designs, namely the Blumlein line (BL) and the pulse forming line (PFL), both featuring nearly identical 100 ns pulse durations, to investigate various cellular effects. Although the primary pulse waveforms were nearly identical in electric field and frequency distribution, the post-pulses differed between the two designs. The BL's post-pulse was relatively long-lasting (~50 µs) and had an opposite polarity to the main pulse, whereas the PFL's post-pulse was much shorter (~2 µs) and had the same polarity as the main pulse. Both post-pulse amplitudes were less than 5% of the main pulse, but the different post-pulses caused distinctly different cellular responses. The thresholds for dissipation of the mitochondrial membrane potential, loss of viability, and increase in plasma membrane PI permeability all occurred at lower pulsing numbers for the PFL than the BL, while mitochondrial reactive oxygen species generation occurred at similar pulsing numbers for both pulser designs. The PFL decreased spare respiratory capacity (SRC), whereas the BL increased SRC. Only the PFL caused a biphasic effect on trans-plasma membrane electron transport (tPMET). These studies demonstrate, for the first time, that conditions resulting from low post-pulse intensity charging have a significant impact on cell responses and should be considered when comparing the results from similar pulse waveforms.