Light Emission from the Surface of Spike-type Discharge Electrode at Negative Corona Discharge in a Non-Thermal Plasma Reactor

[[abstract]]In the past, many experimental investigations for glow or streamer corona induced plasma were conducted by digital real-time or high frame-rate CCD cameras. For example, the light emission profiles at the surface of the spike-type discharge electrode were changing from mono to dual distribution with increasing applied voltage. However, the light emission by CCD camera may mislead the actual plasma or corona discharge channel near the discharge electrode, since a strong corona discharge usually excites the second positive band of the nitrogen molecule (wave length 310 to 340 nm) that is not overlapping with visual or CCD observed spectra (wave length from 400 nm blue to 700 nm red). Therefore, in this work the light emissions observed by the CCD camera and optical spectrometers were compared and used for detailed analysis in order to determine the effect of applied voltage as well as the geometry effect in a non thermal spike-plate plasma reactor. Experimental results show almost a linear increase of spectral intensity of 316-340 nm wavelengths with an applied voltage up to 24 kV, after which the intensity decreases with increasing applied voltage. Normalized wavelength intensities of the second positive band of nitrogen molecule (340 nm wavelength) show a symmetrical profile around the maximum value for applied voltages of 15 and 22 kV. However, the actual location of the maximum of emission intensity at 15 kV is approximately 0.5 mm shifted to the left of the center of the electrode. In contrast, the optical emission profile of the visual spectra at 22 kV has bimodal distribution. Similar profile of the visual spectra was also observed by a CCD camera. Additionally, the optical emission of the second positive band of the nitrogen molecule is directly proportional to the electron density and indirectly proportional to the negative ion density. However, the optical emission of the visual wavelength is directly proportional to the photon density and is indirectly proportional to density of molecules in excitation state rather than to the electron or ion density. Therefore, the light emission from the CCD camera is not actually representative of a corona discharge or a plasma channel. Hence, all detailed investigations for any discharge plasma applications must be by optical spectrometers.[[fileno]]2030213030062[[department]]資訊工程學