Spatial characteristics of nanosecond pulsed micro-discharges in atmospheric pressure He/H2O mixture by optical emission spectroscopy

Atmospheric pressure micro-discharges in helium gas with a mixture of 0.5%water vapor between two pin electrodes are generated with nanosecond overvoltage pulses.The temporal and spatial characteristics of the discharges are investigated by means of time-resolved imaging and optical emission spectroscopy with respect to the discharge morphology,gas temperature,electron density,and excited species.The evolution of micro-discharges is captured by intensified CCD camera and electrical properties.The gas temperature is diagnosed by a two-temperature fit to the ro-vibrational OH(A^(2)Σ^(+)–X^П(2),0–0)emission band and is found to remain low at 425 K during the discharge pulses.The profile of electron density performed by the Stark broadening of Ha 656.1-nm and He I 667.8-nm lines is uniform across the discharge gap at the initial of discharge and reaches as high as 10^(23)m^(-3).The excited species of He,OH,and H show different spatio-temporal behaviors from each other by the measurement of their emission intensities,which are discussed qualitatively in regard of their plasma kinetics.

Effect of power parameters on microdischarge induced by corona discharge

This research mainly describes the generation and diagnosis of plasma using a wire-plate discharge device driven by different power supplies,aimed at investigating the effect of driving source parameters on micro-discharge induced by a corona.The influence of parameters such as waveform,duty ratio and bias voltage on discharge characteristics was explored preliminarily.Experiment results show that the determination of volt-ampere characteristics under different driving source waveforms indicates that the application of square and pulse waveforms shows great advantages over that of sawtooth and sinusoidal waveforms.Similarly,the photo-thermal effects of the system were investigated by comparing the high-voltage electrode temperature and relative emission intensity of N2(C^3Πu—>B^Πg,0-0,337 nm),where square and pulse waveforms also achieved better performance.But the pulse waveform had a slight advantage over the square waveform in terms of energy conversion.Further,investigations of the duty ratio and bias voltage applied on the pulse waveform were conducted,and the results indicate that the duty ratio could effectively improve the discharge power and thermal effect to a certain extent;however,the application of bias voltage on the pulse signal had little influence on the discharge power and thermal effect.

Effect of megapore particles packing on dielectric barrier discharge,O_(3) generation and benzene degradation

Recently,packed-bed discharge plasma technologies have been widely studied for treatment of volatile organic compounds(VOCs),due to the good performance in improving the degradation and mineralization of VOCs.In this paper,a coaxial cylindrical dielectric barrier discharge reactor packed with porous material of micron-sized pores was used for degradation of benzene,and the discharge characteristics and ozone generation characteristics were studied.When the discharge length was 12 cm and the filling length was 5 cm,the packed particles in the discharge area significantly increased the number of micro-discharges,and the current amplitude and density increased with the pore size of packed particles,but the discharge power and ozone concentration showed a trend of first increasing and then decreasing.The discharge power and ozone production reached the maximum when the size of pore former was 75μm,correspondingly,the degradation efficiency of benzene was the highest.

Pre-breakdown to stable phase and origin of multiple current pulses in argon dielectric barrier discharge

We report on the results of numerical models of the(i)initial growth and(ii)steady state phases of atmospheric-pressure homogeneous dielectric barrier discharge in argon.We employ our new inhouse code called Py DBD,which solves continuity equations for both particles and energy,shows exceptional stability,is accelerated by adaptive time stepping and is openly available to the scientific community.Modeling argon plasma is numerically challenging due to the lower speeds of more inertial ions compared to more commonly modeled neon and helium,but its common use for plasma jets in medicine makes its modeling compelling.Py DBD is here applied to modeling two setups:(i)the exponential growth from natural electron-ion seeds(onset phase)until saturation is reached and(ii)the multiple current pulses that naturally appear during the steady state phase.We find that the time required for the onset phase,when the plasma density grows from 10^(9)m^(-3)to 10^(17)m^(-3),varies from 80μs at 4.5 k V down to a fewμs above 6.5 k V,for voltage frequency f=80 k Hz and gap width d_(g)=0.9 mm.At the steady state,our model reproduces two previously observed features of the current in dielectric barrier discharge reactors:(1)an oscillatory behavior associated to the capacitative character of the circuit and(2)several(N_(p))current pulses occurring every half sinusoidal cycle.We show that the oscillations are present during the exponential growth,while current pulses appear approaching the steady state.After each micro-discharge,the gas voltage decreases abruptly and charged particles rapidly accumulate at the dielectric boundaries,causing avalanches of charged particles near the reactor boundaries.Finally,we run a parametric study finding that N_(p)increases linearly with voltage amplitude V_(amp),is inversely proportional to dielectric gap d_(g)and decreases when voltage frequency f increases.The code developed for this publication is freely available at the address https://github.com/gabersyd/PyDBD.