Image process discharge classification under nonuniform fields in air and He at low pressure

This paper described the discharge classification under nonuniform electric field in air and He at low gas pressures for the application of HV technology to the power apparatus in space. In order to discuss quantitatively the change of the discharge, an image processing method was introduced. In the first place, four shape parameters were proposed to characterize the discharge pattern: the area S_H, the flatness rate H/V, the location g of the center of luminosity of the luminous area, and the length L of the positive column. The analysis with the image processing for air revealed that S_H, H/V and g continuously increased as the pressure decreased. Consequently, the discharge type in air was successfully classified into three regions with two boundary pressures 200 and 2000 Pa over the pressure range from 1.3×10⁴ to 27 Pa. The discharge in He was also analyzed in the same way. Another parameter, the effective current density J_e, was introduced, which was defined as a ratio of the discharge current to the luminous area viewed from the vertical direction. J_e proved to be independent of the discharge current I_d, so that there is the possibility that J_e , was suggested as a universal parameter to classify the discharge in a nonuniform electric field in vacuum