Pulse Rise Rate Research Articles

Modeling of discharge characteristics and plasma chemistry in atmospheric CO2 pulsed plasmas employing deep neural network

In recent years, non-thermal plasma technology has emerged as one of the most promising candidates for decomposing CO 2. The fluid model, a powerful tool to investigate the plasma dynamics, is computationally costly in simulating complex CO 2 plasma with tens of particles and hundreds of reactions, especially driven by short pulsed voltages. In this paper, a deep neural network (DNN) is proposed to describe the discharge characteristics and plasma chemistry of CO 2 pulsed discharge at atmospheric pressure. The DNN is trained using the simulation data obtained from the fluid model and then continuously optimized by minimizing the loss function. The effectiveness and feasibility of the DNN are verified by comparing with the experimental measurement and the numerical simulation results. Compared to the time-consuming fluid simulations with tens of hours, the well-trained DNN typically requires only a few seconds to obtain the essential characteristics of CO 2 pulsed discharges with high accuracy, significantly improving the computational efficiency. The DNN prediction results show that increasing the pulse rise rate at a given voltage amplitude can effectively raise the discharge current and breakdown voltage, and the electric field in the sheath region also increases with the pulse rise rate. In addition, the density of the surface charge accumulated on the dielectric layer increases with the plateau duration, and then a strong induced electric field by the surface charges is established, which obviously improves the discharge current during the pulse fall phase. The predicted data also show that increasing the pulse rise rate and the plateau duration could effectively improve the density of product species, such as CO and O 2, leading to an increase in CO 2 conversion. This study demonstrates that the DNN method is a reliable tool for obtaining the essential discharge characteristics of atmospheric CO 2 pulsed plasma and provides a promising avenue for future applications of DNN-based methods in non-thermal plasmas.

Few-nanosecond stripline kickers for top-up injection into PETRA IV

PETRA IV is the planned ultralow-emittance upgrade of the PETRA III synchrotron light source at DESY, Hamburg. The current baseline injection scheme is an off-axis, top-up injection with few-nanosecond stripline kickers, which would allow for accumulation and least disturbance of experiments during injection. Besides the requirements on kick-strength, field quality, pulse rise-rate, and heat management, two mechanical designs with different apertures are necessary, as the devices will be used for injection and the transverse multi-bunch feedback system. In this contribution we will present the current status of 3D finite element simulations of electromagnetic fields as well as the mechanical design and first pulse electronics tests.

Direct comparison of silicon carbide and silicon diode avalanche shaper in multi-pulse applications

This paper compares the pulse shaping characteristics of SiC and Si Diode Avalanche Shaper (DAS) under quasi-uniform triggering with the help of Technology Computer-Aided Design (TCAD) software. Under the same static breakdown voltage (VSB), the opening speed of SiC DAS does not show obvious advantages over that of Si DAS. With the same device structure, SiC DAS has a higher breakdown voltage than Si DAS, so it has a faster dV/dt in the triggering process. In addition, compared to Si, SiC DAS delayed breakdown voltage (VDB) is less affected by the input pulse rise rate. This is because the SiC DAS avalanche generation rate is more sensitive to the device voltage in the vicinity of VDB. Then, the multi-pulse operating characteristics of SiC and Si DAS with the same VSB were compared by continuously triggering the SiC and Si DAS 50 times at the 1 MHz frequency. It is revealed that the VDB of the SiC DAS is low but has excellent multi-pulse consistency. At the same time, under multi-pulse operation, the temperature rise speed of SiC DAS is slow, and the temperature distribution in the device is more uniform. It can be concluded that SiC DAS has significant advantages in high voltage and multi-pulse shaping.

Comparing Study on Formation of Large Discharge Currents in Atmospheric Pulse-Modulated Radio Frequency Discharges

In recent years, pulse-modulation is introduced in atmospheric radio frequency (RF) discharges to further control the discharge operation. In this article, a comparing study is performed by a 1-D fluid model to investigate the formation of large discharge currents (LDCs) in the first RF cycle during the power-on phase in an atmospheric pulse-modulated RF discharge controlled by dielectric barriers. The current–voltage characteristics and helium metastable (He*) distributions show the enhancement of a pulsed voltage on the ignition of RF discharge, which agrees well with the experimental observation. On the other hand, in a dielectric barrier discharge driven by a sinusoidal voltage of 500 MHz, double LDCs are observed in the positive and negative half-cycles, respectively, and the large pulse rise rate of applied voltage essentially influences the distribution of charged particles in the first cycle during the power-on phase. In this study, according to computational data the reverse electric field near the anode contributes greatly to the generation of LDCs in both types of discharge, and the appropriate discharge conditions are suggested to optimize the pulse-modulated RF discharges in applications.

Comprehensive study on plasma chemistry and products in [formula omitted] pulsed discharges under Martian pressure

With the development of Mars exploration, the In-Situ resource utilization on Mars has been drawn significant attention in recent years. The abundant CO2 in the Martian atmosphere makes it possible to decompose CO2 to produce high-value platform chemicals by plasma technology. In this comprehensive study, the discharge characteristics, products distribution, and reaction pathways in CO2 pulsed discharges under Martian pressure are investigated, and the effects of pulsed waveforms on discharge characteristics and produced species are also discussed. The simulation results show that electrons and CO2+ ions are the main components of charged particles in the discharge region; CO and O are mainly produced by the electron impact dissociation and electron impact attachment reactions with ground state and vibrationally excited state of CO2 during the power-on phase and consumed by the ion–neutral reactions. The recombination reaction of electrons and CO2+ ions is very important for the formation of O2. The simulation data also give the main generation and consumption pathways of vibrationally excited CO2 molecules, and indicate that the vibrational energy of excited CO2 molecules can lower the energy barrier of the reaction and facilitate the decomposition of CO2. In addition, the experimental and computational data also suggest that the pulsed waveforms could affect the discharge characteristics and plasma chemistry in CO2 pulsed discharges under Martian pressure, the densities of product species in CO2 plasma increase with the pulse rise rate and pulse rise duration of pulsed voltage. This study provides an enhanced understanding of discharge characteristics and plasma chemistry in the CO2 pulsed discharges under Martian pressure, and suggests optimized ways to utilize the CO2 on Mars.

Modeling study on the enhancement of atmospheric pulse-modulated radio-frequency discharge assisted by pulsed voltage

In this paper, we performed a one-dimensional fluid model to study the mechanism and optimization of pulse-modulated Radio-Frequency (RF) discharges at atmospheric pressure assisted by short pulse voltages. The evolution of discharge current density, helium metastable (He*) density, and total electron density from the simulation demonstrates that the ignition of RF discharge could be effectively enhanced by the short pulsed discharge, and a large Peak Current in the First Period (PCFP) can be produced, which agrees well with the experimental measurements. Due to the assistance of pulsed voltage, a strong electric field could be formed near the anode with the same polarity of that near the cathode, which can reaccelerate the electrons near the anode to generate a large PCFP. Based on the simulation results, reducing the time interval and increasing the pulse rise rate are very helpful to enhance the ignition of subsequent RF discharge by strengthening the electric field near the anode. It is shown that by choosing the appropriate time interval and pulse rise rate, the pulse-modulated RF discharge assisted by the pulsed discharge can be effectively modulated and optimized for applications.

Experimental Analysis of Breakdown With Nanosecond Pulses for Spark-Ignition Engines

The influence of pulse rise rate and pulse duration for ignition purposes in engines is investigated. A constant volume cell is used to characterize the breakdown voltage under nanosecond pulsed voltages with automotive sparkplugs having electrode gaps ranging from 0.2 mm to 1 mm. Two pulse generators are used to compare pulses with durations of 10 ns and 50 ns. Different pulse amplitudes are used, and air gaps with breakdown voltages ranging from 4 kV to 15 kV are investigated. The cell is filled with synthetic air with densities gap distances products that are relevant for internal combustion engines. This study shows that the pulse shape and rise rate influence the breakdown voltage. Under pulsed discharge, the breakdown voltage is always above the static breakdown voltage. The probability of pulsed discharge breakdown increases as both the pulse amplitude and duration increases. Furthermore, the breakdown voltage value increases with increasing pulse rise rate. The delay time between reaching the static breakdown voltage and the actual breakdown voltage decreases with increasing overvoltage. The delay time is constituted by statistical and formative times. Both the statistical and formative times decrease with increasing overvoltage. For ignition purposes, the pulse rise rate should be as high as possible to deliver a larger energy input in the breakdown phase. Furthermore, for reduced electrode erosion, the pulse duration should be short (10-20 ns) to reduce the probability for a transition to an arc.

Multichannel switching in a multigap gas switch at atmospheric pressure

The multichannel switching mode of a controlled multigap switch is studied. The switch is designed for capacitive energy storage, with a charging voltage of up to 100 kV and an energy output time of about 100 ns. The interval between the high-voltage and low-voltage electrodes of this switch is divided into seven series-connected gaps using ball electrodes, and six parallel rows of these ball electrodes allow for multichannel switching. An optical system based on collimators and photodiodes was used to determine the number of channels in the switch gaps. Statistics on the number of channels were collected and the probability of ignition of parallel spark channels was calculated for each of the switch gaps under different operating conditions. We show that both the electrical isolation between the channels and the rate of rise of the triggering pulse significantly affect the number of parallel ignited channels and their distribution over consecutive gaps. At a high triggering voltage pulse rise rate ($\ensuremath{\sim}800\text{ }\text{ }\mathrm{kV}/\ensuremath{\mu}\mathrm{s}$), a larger number of spark channels are ignited in the switch with electrical isolation between the channels and the characteristics of this switch are better. At a low triggering voltage pulse rise rate (less than $250\text{ }\text{ }\mathrm{kV}\text{ }\ensuremath{\mu}\mathrm{s}$), better characteristics are realized in the switch without electrical isolation between the channels.

Investigation of climate change impacts on flow regime in the Lucas Creek catchment using multiple CMIP5 ensembles

ABSTRACTClimate change is projected to affect the flow regime in urban waterways adversely. This study investigates the climate change impacts on the flow regime in the Lucas Creek catchment under three Representative Concentration Pathways (RCPs): RCP 2.6, RCP 4.5 and RCP 8.5. Flow Duration Curves (FDCs) and Indicators of Hydrological Alteration (IHA) methods are used to assess flow regime variations. Results of FDCs show a maximum rise of 370% in peak flow under RCP 4.5 however, low flow increases by 40%. Monthly streamflow increases up to 380% except for October and December. Similarly, the majority of the IHA parameters also show at least a 10% increase in their magnitudes under RCP 8.5. However, some parameters such as high pulse duration and rise rate decrease by 50% under RCP 4.5. The catchment would mainly suffer severe impact variations under RCP 4.5 and RCP 8.5 in the future.

Analysis and restoration of an ecological flow regime during the Coreius guichenoti spawning period

The development of cascade hydropower in the Yalong River has changed the hydrological regime of the river and sharply reduced the Coreius guichenoti population dwelling downstream of the JinPing II power station. In this paper, an eco-hydrological index system for C. guichenoti habitat was constructed based on Indicators of Hydrologic Alteration (IHA) and Environment Flow Components (EFC), which aimed to coordinate the processes of ecological hydrological and water temperature variations to guarantee the oviposition of C. guichenoti. The analysis revealed that the suitable rise rate and fall rate intervals, which are dimensionless parameters, were 0.05–0.10 and 0.01–0.03, respectively, during the spawning period. The rise and fall durations were both 1–2 days, the cycle of water fluctuations was 3–5 days, the flow pulse duration was 5–7 days, the flow pulse rise rate was 0.56–0.65, and the flow pulse fall rate was 0.23–0.50. Then, the Instream Flow Incremental Methodology (IFIM) method was used to calculate the ecological base flow during the C. guichenoti spawning period. Moreover, the ecological flow regime for C. guichenoti downstream of the JinPing II power station during the spawning period was determined based on eco-hydrological indicators and water temperature requirements. These results showed that the ecological flow regime could not only guarantee oviposition but also meet the drifting conditions required for eggs, and therefore, the ecological operation of diversion-type hydropower stations and cascade hydropower stations needs to be given more attention to provide suitable spawning conditions in target fish habitats.

Modeling study on the effects of pulse rise rate in atmospheric pulsed discharges

In this paper, we present a modeling study on the discharge characteristics driven by short pulsed voltages, focusing on the effects of pulse rise rate based on the fluid description of atmospheric plasmas. The numerical results show that the breakdown voltage of short pulsed discharge is almost linearly dependent on the pulse rise rate, which is also confirmed by the derived equations from the fluid model. In other words, if the pulse rise rate is fixed as a constant, the simulation results clearly suggest that the breakdown voltage is almost unchanged, although the amplitude of pulsed voltage increases significantly. The spatial distribution of the electric field and electron density are given to reveal the underpinning physics. Additionally, the computational data and the analytical expression also indicate that an increased repetition frequency can effectively decrease the breakdown voltage and current density, which is consistent with the experimental observation.

A high-voltage high-current switch on the basis of triggered vacuum switches

A KV-25-300 high-voltage switch for dc voltages of up to 25 kV and currents of up to 300 kА for pulse powering of loads at a pulse rise rate of up to 10 kA/μs was developed and tested. The switch consists of two series-connected RVU-43-1 triggered vacuum switches, thus making it possible to reduce the breakdown probability at the maximum operating voltage to a value of <10–7. The total switching-on time delay relative to the optical control pulse is 4 ± 0.5 μs. The results of measurements and calculation of the electric strength of RVU-43-1 and KV-25-300 and the results of switching tests of the latter are presented.

A control unit of the cold-cathode thyratron with a high pulse repetition rate

A compact high-voltage pulse generator is designed for control of TDI thyratrons in grounded-cathode thyratron-switching circuits. The unit is the part of the pulse voltage generator for charging a double forming line of the frequency electron accelerator. The unit is controlled from the GZI-6 external generator with a maximal repetition rate of 50 s−1. The unit produces negative-polarity firing voltage pulses with a ∼18-kV/μs rate of pulse rise and allows one to fire simultaneously two TDI4-100k/75PD thyratrons. The scatter of amplitudes of currents of thyratrons, connected in parallel without additional current-dividing circuits, does not exceed 1%. The efficiency factor of the control unit is approximately 85%. The active elements of the control unit are the thyristor and the TGI-500/16 low-power pulse hydrogen thyratron.

Effects of pulse voltage rise rate on velocity, diameter and radical production of an atmospheric-pressure streamer discharge

The effect of pulse rise rate on a streamer discharge is investigated through both experiments and simulations. Pulsed voltages with a pulse rise rate of 0.11–0.52 kV ns−1 are applied to point-to-plane electrode configurations, and the effects are observed from ICCD photographs. The streamer emission of light is simulated by a previously developed two-dimensional streamer simulation model, and the simulation results are compared with experimental results. The results show that as the pulse rise rate is decreased, there is a decrease in the discharge current, velocity of the primary streamer, diameter of the streamer channel and emission length of the secondary streamer. The simulated reduced electric field of the primary streamer head remains constant and does not depend on the pulse rise rate. The simulated temporal variations of O and OH radical production show that almost the same number of the radicals are produced in the primary streamer, regardless of the pulse rise rate. However, the radical production in the secondary streamer decreases as the pulse rise rate decreases. Therefore, the pulse rise rate affects the ratio of radical production in the primary streamer to that in the secondary streamer.

Multichannel Discharge Characteristics of Gas Switch Gap in SF6-N2 or SF6-Ar Gas Mixtures Under Nanosecond Triggering Pulses

Experiments were carried out to ascertain multichannel discharge characteristics in a self-designed coaxial field-distortion gas switch filled with SF6-N2 or SF6-Ar gas mixtures of different mixing ratios. In these experiments, the pressure varied from 0.1 MPa to 0.2 MPa, the voltage pulse peak applied to the switch was in the range from 40 kV to 78 kV, and the pulse rise time was 11 ns. The static breakdown strength of the gas switch gap in the switch was also measured. The results show that in general the average number of discharge channels for SF6-Ar or SF6-N2 gas mixture which contains less SF6 is larger than that for gas mixture which contains more SF6, however, the average number of channels almost keeps constant as the gas mixing ratio varies when the pulse rise rate is high enough. The static breakdown strength of the gas switch gap decreases slightly as the content of argon or nitrogen increases.

A trapezoidal pulse generator with independent adjustments of amplitude and slopes of leading and trailing edges

A trapezoidal pulse generator with independent adjustments of slopes of leading and trailing edges of pulses and their amplitudes is described. The circuit can also operate as a continuous triangle-pulse generator. The maximal pulse rise rate is 1 V/μs, when the maximal pulse amplitude is 5 V.

Dependence of the criterial levels of damage in semiconductor structures under the action of high-power electromagnetic pulse on the pulse rise rate

It is demonstrated that the criterial (critical) levels of thermal damage of the semiconductor structures with p-n junctions depend on both electromagnetic pulse energy and power and the pulse rise rate. The temperature of destruction of the junction that is found from the solution to the heat-conduction equation is chosen as the critical damage level. At a constant pulse power, the energy needed for the damage decreases with increasing pulse rise rate.

Generation of surface gravity waves by bottom time-repetitive pulses

We investigate the deviation of free surface, generated by two repetitive excitations of the bottom surface, within the framework of model of a liquid of finite depth. The liquid is assumed to be incompressible and inviscid, which allows us to consider the problem in the potential statement. The problem is solved on the basis of the Hankel integral transformation by the radial coordinate and Laplace integral transformation by time with subsequent numerical inversion. We present and analyze some numerical results for the case of axially symmetric disturbance of the horizontal bottom surface (underwater earthquake). We show the appearance of waves with growing amplitudes for certain values of the time delay and increase in the rate of pulse rise. We also show that an increase in the pulse sharpness (its rise with time) will cause an increase in the amplitude.

Speed of streamers in argon over a flat surface of a dielectric

A pin–pin electrode geometry was used to study the velocities of streamers propagating over a flat dielectric surface and in gas close to the dielectric. The experiments were done in an argon atmosphere, at pressures from 0.1 to 1 bar, with repetitive voltage pulses. The dielectric surface played a noticeable role in discharge ignition and propagation. The average speed of the discharge decreased with higher pressure and lower voltage pulse rise rate. It was higher when the conductive channel between the electrodes was formed over the dielectric, rather than through the gas. Space resolved measurements revealed an increase in velocity of the discharge as it travelled towards the grounded electrode.

Improvement of diagnostic techniques and electrical circuit in azo dye degradation by high voltage electrical discharge

Fast electrical diagnostics and improvement of electrical circuits for methyl orange (MO) degradation by high voltage pulsed electrical discharge were investigated. To eliminate electromagnetic radiation, several effective methods were employed. RG 218 coaxial cable was substituted for the common transmission lines to transmit high voltage pulses, and multi-lines in parallel were earthed to avoid electromagnetic interference and, additionally, to reduce the stray inductance of the electrical circuit and increase the pulse rise rate to reduce the energy losses in the transmission system. The problem of the differences in the bandwidths of voltage and current probes causing an error in the calculation of energy dissipation was avoided by reducing the bandwidths of voltage and current measurements to the same value. The real discharge current was obtained by subtracting the capacitive current from the total current. The energy per pulse obtained in the reactor before and after improvement of the diagnostics and electrical circuit were 15.5 mJ and 26.8 mJ, respectively, and the energy efficiencies of MO degradation were 1.34 × 10 −9 mol/J and 1.95 × 10 −9 mol/J, respectively.