Studies On The Spatial-resolved Optical Emission Spectrum Of Spark Discharge In Air Over Water Cathode

Spark discharge in air over water cathode has many physical and chemical synergistic degradation functions such as ultraviolet,high electric field ionization,and active particle oxidation.It has the advantages of fast degradation rate,large treatment area and no secondary pollution in the disinfection and sterilization of toxic waste water.It is considered as the most potential oxidation technology.Recently,the plasma parameters of the spark discharge in air over water cathode,such as electron density,electron temperature and gas temperature,has been intensively investigated by measuring the optical emission spectrum of the spark filament.Due to the relatively weak light emission,it is very difficult to measure the emission spectrum of a single spark filament,leading to a lack of research on the spatial distribution characteristics of plasma parameters in spark channel.In this paper,a self-constructed ultra-high speed spatial-temporal resolution spectrometer was used to study the spatial-resolved emission spectra of spark discharge in air over water cathode.The spatial resolved spectra of H?line and N atomic lines were measured during a single discharge pulse and cumulative 10 pulses,respectively.The distribution characteristics of electron density and electron temperature along the axis of the spark discharge channel have been studied.The main results are as following:?1?The average value of electron density and electron temperature obtained from one single pulse measurement and 10-pulse cumulative measurement have no significantly different.They have the same tendency in spatial distribution along the axial direction of the spark channel.The multiple-pulse cumulative measurement has large number of samples and high signal-to-noise ratio,hence is more suitable for data processing.?2?The electron density was measured from the H_?spectral line and the N?746 nm?atomic spectrum.The electron density obtained by using N?746 nm?atomic spectra is about twice times as large as that obtained by using the H_?line.It is mainly caused by the influence of the gas pressure in the spark discharge channel on the Van der Waal broadening of N?746nm?.The H_?spectral line is more suitable for the electron density measurement of the spark discharge channel.?3?The electron density in the spark discharge channel is roughly within the range of3.088×10²²².07×10²33 m^-3,and decreases with increasing the distance from the anode tip.?4?The electron temperature in the spark discharge channel is between 7500⁹000 K,and keeps nearly constant along the axial direction.