Comparing plasma fluid models of different order for 1D streamer ionization fronts

We evaluate the performance of three plasma fluid models: the first order reaction-drift-diffusion model based on the local field approximation; the second order reaction-drift-diffusion model based on the local energy approximation and a recently developed high order fluid model by Dujko et al (2013 J. Phys. D 46 475202) We first review the fluid models: we briefly discuss their derivation, their underlying assumptions and the type of transport data they require. Then we compare these models to a particle-in-cell/Monte Carlo (PIC/MC) code, using a 1D test problem. The tests are performed in neon and nitrogen at standard temperature and pressure, over a wide range of reduced electric fields. For the fluid models, transport data generated by a multi-term Boltzmann solver are used. We analyze the observed differences in the model predictions and address some of the practical aspects when using these plasma fluid models

Comparing plasma fluid models of different order for 1D streamer ionization fronts

We evaluate the performance of three plasma fluid models: the first order reaction-drift-diffusion model based on the local field approximation; the second order reaction-drift-diffusion model based on the local energy approximation and a recently developed high order fluid model by Dujko et al (2013 J. Phys. D 46 475202) We first review the fluid models: we briefly discuss their derivation, their underlying assumptions and the type of transport data they require. Then we compare these models to a particle-in-cell/Monte Carlo (PIC/MC) code, using a 1D test problem. The tests are performed in neon and nitrogen at standard temperature and pressure, over a wide range of reduced electric fields. For the fluid models, transport data generated by a multi-term Boltzmann solver are used. We analyze the observed differences in the model predictions and address some of the practical aspects when using these plasma fluid models.</p

Comparing plasma fluid models of different order for 1D streamer ionization fronts

We evaluate the performance of three plasma fluid models: the first order reaction-drift-diffusion model based on the local field approximation; the second order reaction-drift-diffusion model based on the local energy approximation and a recently developed high order fluid model by Dujko et al (2013 J. Phys. D 46 475202) We first review the fluid models: we briefly discuss their derivation, their underlying assumptions and the type of transport data they require. Then we compare these models to a particle-in-cell/Monte Carlo (PIC/MC) code, using a 1D test problem. The tests are performed in neon and nitrogen at standard temperature and pressure, over a wide range of reduced electric fields. For the fluid models, transport data generated by a multi-term Boltzmann solver are used. We analyze the observed differences in the model predictions and address some of the practical aspects when using these plasma fluid models.</p

Investigation of positive streamers by double pulse experiments

Streamer discharges are influenced by background ionization and other effects of previous discharges. We have studied the influence of repeating positive streamer discharges by applying two subsequent high voltage pulses with a variable interval (200~ns to 40~ms) between them. The discharges are studied with two ICCD cameras that image the discharge during either the first or the second voltage pulse. Experiments have been performed in a 103~mm point-plane gap at a pressure of 133~mbar in artificial air, pure nitrogen and pure argon. We have found a range of phenomena that depend on the inter-pulse time ¿t. For small ¿t, (below 1~µs for air and nitrogen and below 15~µs for argon) the streamers just continue their old paths. At larger ¿t the conductivity has decreased too much for such continuation. However, parts of the old paths do glow up again like secondary streamers. At still larger ¿t (roughly above 2.5~µs for air and 30~µs for nitrogen) new channels appear. At first they avoid the entire area of the previous discharge; next they follow the edges of the old channels; then they start to follow the old channels exactly and finally (¿t>1~ms) they become fully independent of the old paths

Investigating heating dynamics in sparks

After the first streamer discharge front in a spark, heating and gas expansion sets in.This effect underlies the streamer to leader transition in air, and becomes strongerwith increasing density of the medium. We model and solve heat generation by the discharge,the thermal shock and the induced pressure wave. In particular, we investigate the electric breakdown of supercritical nitrogen and the subsequent recovery of insulation, motivated by a possible applicationas a high voltage switch

Streamer to spark transition in supercritical N2

We model the streamer to spark transition in supercritical nitrogen as this is a promising medium for electrical switching. We assume that the streamer has bridged the gap and that a weakly ionized channel with a constant field has formed. We model how the discharge energy is transferred from kinetic energy of electrons into particular molecular excitations and further into gas heating, and how the thermal expansion of the discharge channel sets in.</p

Investigating heating dynamics in sparks

After the first streamer discharge front in a spark, heating and gas expansion sets in.This effect underlies the streamer to leader transition in air, and becomes strongerwith increasing density of the medium. We model and solve heat generation by the discharge,the thermal shock and the induced pressure wave. In particular, we investigate the electric breakdown of supercritical nitrogen and the subsequent recovery of insulation, motivated by a possible applicationas a high voltage switch

Numerical and experimental investigation of dielectric recovery in super-critical Nitrogen

A supercritical (SC) nitrogen (N2) 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 N2 switch under high repetition rate operation, a numerical model is developed. For SC N2 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 Taxis = 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

Breakdown strength and dielectric recovery in a high pressure supercritical nitrogen switch

Fast and repetitive switching in high-power circuits is a challenging task where the ultimate solutions still have to be found. We proposed a new approach. Supercritical fluids (SCFs) combine favorable properties of liquids - insulation strength, thermal behavior, and gases - self healing, high fluidity, and absence of vapor bubbles. That's why we start investigating the subject of plasma switches in SC media. First results indicate excellent switch recovery and very high insulation strength. We present the design of a SCF insulated switch (SC switch). Breakdown strength of the SCF is investigated and found to be high in comparison with most of the solid insulating media. The dielectric recovery inside the SC N2 switch is tested under a repetitive 30 kV, 200 ns pulse voltage at repetition rate up to 5 kHz. The recovery breakdown voltage across the SC switch achieves 80 % within 200 µs. The current interruption capability of SC N2 is investigated experimentally in a synthetic circuit generating a high-frequency arc of several hundreds of amperes and a transient recovery voltage of hundreds of volts. The results show that a SC N2 switch with fixed electrodes and an inter-electrode distance of mm range can successfully interrupt this current at approximately 2 ms after arc initiation