Subnanosecond processes in the stage of breakdown formation in gas at a high pressure

The paper analyzes the data obtained in the subnanosecond time range on the times (t br) and speeds (V br) of switching of hydrogen diode dischargers. These data were obtained in a wide range of hydrogen pressures (p) and the degree of the discharge gap overvoltage (the length of the cathode-anode gap d) in a uniform electric field. It is shown that the reduced strength of the average electric field E br/p in the discharge gap at the moment of the beginning of the breakdown significantly decreases when the gas pressure increases from 5 atm to 50 atm. An increase in pressure from 50 atm to 60 atm leads to a sharp (by 40–135%, depending on the d) increase in the pulse breakdown voltage (U br) and an increase in E br/p. In proportion to the growth of E br/p the switching speed V br of the discharge gas gap increases. The observed effect is explained by the change in the discharge initiation mechanisms. The limitation of U br and V br in the hydrogen pressure range from 5 atm to 50 atm occurs as a result of gas ionization by runaway electrons and the subsequent development of a multi-avalanche discharge in the volume of the discharge gap. With a further increase in pressure, the discharge develops according to the streamer type. To design ultrafast gas dischargers of the subnanosecond range intended for switching high voltages, it is necessary to select an appropriate range of working gas pressures in order to ensure the development of a streamer-type discharge.

Section: Introductionsupporting

confidence: 68%

Investigation of the switching characteristics of high-pressure subnanosecond gas dischargers with the purpose of a sharp increasing of the breakdown voltages and the switching speed

Ivanov¹

2022

“…Characteristic delay times for high-voltage breakdowns in a non-uniform electric field at a nitrogen pressure of 2-9 MPa are reported in [99]. Analysis of these experimental data, including data on breakdown voltages and discharge dynamics in space and time, suggests that most of the delay time falls on the breakdown formation time τ br because the statistical delay (the generation time of one or several primary electrons) at high gap overvoltages is much smaller than τ br .…”

Section: Radiationmentioning

confidence: 99%

“…However, the ionization wave transit times 0.4-0.6 ns approximated the time resolution of the AGAT-SF3M camera [99]. Moreover, the time resolution of the device was decreased because the slit width was increased to ∼2 mm.…”

Section: Radiationmentioning

confidence: 99%

“…Thus, higher resolution is needed to obtain more detailed data on ionization waves in subnanosecond breakdowns. Besides, the electrode configuration (cylindrical cathode, semispherical anode with a cylindrical protrusion) provided a quasisymmetric non-uniform electric field [99][100][101], which resulted in electron avalanches and ionization waves from different zones of the discharge gap and made the study difficult. For research in the dynamics of subnanosecond breakdowns, it is likely preferable to use electrode configurations which provide an asymmetric electric field with its amplification at one of the electrodes to fix the onset of ionization processes.…”

Section: Radiationmentioning

confidence: 99%

See 1 more Smart Citation

Subnanosecond breakdown in high-pressure gases

Naidis

Тарасенко

Babaeva

et al. 2018

Pulsed discharges in high-pressure gases are of considerable interest as sources of nonequilibrium plasma for various technological applications: pollution control, pumping of laser media, plasma-assisted combustion, etc. Recently, attention has been attracted to the use of subnanosecond voltage fronts, producing diffuse discharges with radii of several millimeters. Such plasma structures, similar to pulsed glow discharges, are of special interest for applications due to quasi-uniformity of plasma parameters in relatively large gas volumes. This review presents the results of experimental and computational study of subnanosecond diffuse discharge formation. A description of generators of short high-voltage pulses with subnanosecond fronts and of discharge setups is given. Diagnostic methods for the measurement of various discharge parameters with high temporal and spatial resolution are described. Obtained experimental data on plasma properties for a wide range of governing factors are discussed. A review of various theoretical approaches used for computational study of the dynamics and structure of fast ionization waves is given; the applicability of conventional fluid streamer models for simulation of subnanosecond ionization waves is discussed. Calculated spatial-temporal profiles of plasma parameters during streamer propagation are presented. The efficiency of subnanosecond discharges for the production of reactive species is evaluated. On the basis of the comparison of simulation results and experimental data the effects of various factors (voltage rise time, polarity, etc.) on discharge characteristics are revealed. The major physical phenomena governing the properties of subnanosecond breakdown are analyzed.

“…So the electric energy input is considered to be equal to the electron component of the electric energy Q R = Q e . After the streamer bridges the gap, the electric field E is assumed to be uniform in the gap [52]. For a given E, the electron energy deposition rate can be calculated with the equation Q e = σ e E 2 = q e µ e n e E 2 , where σ e is the electrical conductivity due to electron mobility; q e , µ e and n e are the electron charge, mobility and number density of electrons, respectively.…”

Section: Streamer-to-spark Transition Phasementioning

confidence: 99%

Numerical and experimental investigation of dielectric recovery in supercritical N₂

Zhang

Markosyan

Seeger

et al. 2015

A supercritical (SC) nitrogen (N 2 ) switch is designed and tested. The dielectric strength and recovery rate of the SC switch are investigated by experiments. In order to theoretically study the discharge and recovery process of the SC N 2 switch under high repetition rate operation, a numerical model is developed. For SC N 2 with initial parameters of p = 80.9 bar and T = 300 K, the simulation results show that within several nanoseconds after the streamer bridges the switch gap, the spark is fully developed and this time depends on the applied electric field between electrodes. During the whole discharge process, the maximum temperature in the channel is about 20 000 K. About 10 µs after the spark excitation of 200 ns duration, the temperature on the axis decays to T axis 1500 K, mainly contributed by the gas expansion and heat transfer mechanisms. After 100 µs, the dielectric strength of the gap recovers to above half of the cold breakdown voltage due to the temperature decay in the channel. Both experimental and numerical investigations indicate that supercritical fluid is a good insulating medium that has a proved high breakdown voltage and fast recovery speed.