Research On Properties Of Magnetic-assisted DC Superimposed Nanosecond Pulsed Streamer Discharge

When the duration of the applied pulse voltage is shortened to nanoseconds and submicroseconds,it is difficult to transfer the energy of the pulse source to the reactor to the maximum extent in pulsed discharge.Improving the impedance matching between the pulse source and the reactor is the key to effective energy conversion.In addition,in the case of good matching,further improving discharge energy utilization and plasma chemical activity is also crucial.This study develops a magnetic-assisted DC superimposed nanosecond pulsed streamer discharge system.The physical and chemical characteristics of magnetic-assisted DC superimposed nanosecond pulsed streamer discharge plasma,such as discharge characteristics,streamer propagation behavior and active material generation,are systematically studied.The electrical characteristics,optical characteristics and ozone synthesis characteristics of DC superimposed nanosecond pulsed streamer discharge are investigated.And the dynamic evolution law of streamer and the types and distribution characteristics of active substances are studied.It is found that the impedance matching between the pulse source and the reactor is effectively improved by adding DC voltage,and the input energy of the pulse source to the reactor is increased.It is mainly presented that the discharge conduction current and average power increase with the increase of DC voltage,as well as the number of streamer channels.In addition,it is found that the propagation velocity of primary and secondary streamers increases significantly after the superposition of DC voltage,and the propagation distance of secondary streamers also increases with the increase of DC voltage.The species,density,distribution range of active substances increase with the increase of DC voltage as well as ozone concentration.The effects of magnetic field on the electrical characteristics,discharge light intensity,reduced field intensity,dynamic evolution of streamer and ozone synthesis characteristics of DC superimposed nanosecond pulsed streamer discharge plasma are studied.It is found that the magnetic field can improve the discharge intensity by changing the electron trajectory and the binding effect on electrons.The discharge current,power and energy are significantly improved with magnetic field.The discharge light intensity and the number of flow channels increases significantly as well as the emission spectrum intensity of each active substance.In addition,the velocity of the primary streamer increases significantly with the magnetic field,while the secondary streamer is almost unaffected.The magnetic field increases the discharge reduction field strength,and improves the ozone production and ozone synthesis energy efficiency.It is considered that the magnetic field mainly affects the trajectory of high energy electrons(mostly produced in primary streamer).The binding effect of magnetic field on high-energy electrons effectively reduces the neutralization loss of high-energy electrons,resulting in a faster increase in the number of high-energy electrons than low-energy electrons during magnetic field-assisted discharge,which is the main reason for improving the reduced field strength,ozone production and energy efficiency.The effects of magnetic field intensity and wire-plate distance on magnetic-assisted DC superimposed nanosecond pulsed streamer discharge were investigated through the means of discharge current,discharge power,photocurrent signal and ozone detection,and the parameters of magnetic field and wire-plate distance are optimized.Under the optimal magnetic field conditions,the feasibility of the application of magnetic-assisted DC superimposed nanosecond pulsed streamer discharge in toluene degradation is verified.It is found that the magnetic field has an enhancement effect on the discharge,and the enhancement effect increases with the increase of the magnetic field and decreases with the decrease of wire-plate distance.The degradation experiment showed that the magnetic-assist DC superimposed nanosecond pulsed streamer discharge has excellent ability of toluene degradation.