Optical Measurements Of The Electric Field At The Streamer Head Of Nanosecond Pulsed Underwater Corona Discharges Based On Kerr Effect

Recently underwater electrical discharges have attracted intensive attention for its potential application on water or wastewater treatment. Previous works have shown that many organic compounds contained in the wastewater can be efficiently degraded by underwater electrical discharges. Some microorganisms contained in drinking water also can be killed by underwater electrical discharges. Generally, the underwater electrical discharges initiate both physical and chemical processes, such as high electrical field, ultraviolet radiation, bubble, Shockwave, and formation of chemical reactive species. The electric field at the streamer head plays an important role in the streamer propagation and the formation of chemical reactive species. It is difficult to measure the electric field at the streamer head of underwater pulsed corona discharge.In this work, an optical measurements of the electric field at the streamer head of nanosecond pulsed underwater corona discharges was performed basing on the Kerr effect. An optical measurement system was established by using an ultrahigh-speed camera system with four intensified charge-coupled device (ICCD) camera modules. This system enables ultrafast recording of up to four full frame resolution images with a1-ns inter-frame time, allowing us to study the temporal evolution of electric field at the streamer head.An image processing program was developed by using MATLAB. It can read and display the16bit TIFF images record by the ultrahigh-speed camera system and select the streamer head range for electric field calculation. The results of the electric field at the streamer head can be presented as a contour figure of the electric field distribution.The calculation of electric field involves an Abel inversion problem. In this work, Fourier-Hankel transform method was employed to solve the Abel inversion problem. For this purpose several data smoothing methods were compared and the Savitzky-Golay polynomial method was select to smooth our experimental data.The images obtained in our experiments were processed by our image processing program. The temporal evolution of electric field at the streamer head during the streamer propagation was investigated. The electric fields at the streamer head of different streamer branches at the same time were compared. The result shows that the electric field at streamer head varies with the time during the streamer propagation, the total average of it is of about700kV/cm. Several streamer branches form during the corona discharge. However the electric field at the head of each streamer branch has different value at the same time.