[Discharge characteristic and spectrum measurement of a new type of single filament in a dielectric barrier discharge].

A new type of single filament was observed in a dielectric barrier discharge (DBD) system for the first time. It was formed with a larger discharge gap (d=3. 8 mm) and a smaller discharge area (S= 1 cm x 1 cm) in an air/argon gas mixture. Compared with the single filament observed by other experimental groups, the new type of single filament is composed of volume discharge (VD) and surface discharge (SD). In addition, the single filament has excellent discharge stability and sustainability. In order to study more about the discharge characteristic of the new type of single filament in a half-cycle of the applied voltage and the plasma state in different positions of the discharge column in the side view of the new type of single filament, both a high speed framing camera (HSFC) and a spectrograph were used in the experiment. The instantaneous images of end and side view of the new type of single filament were taken by the HSFC with different exposure time, and the discharge characteristic of the new type of single filament in a half-cycle of the applied voltage was compared with that of glow discharge. The spectral lines of Ar I 763. 26 nm (2P6-->1S5) and Ar I 772.13 nm (2P2-->IS3) in different positions of the discharge column of the new type of single filament were measured by using optical emission spectra, and chosen to estimate the corresponding electron excitation temperature by the relative intensity ratio method. It was found that the new type of single filament is composed of VD and SD, and SD produces a dendritic discharge around VD. The discharge characteristic of the new type of single filament in a half-cycle of the applied voltage is similar to that of glow discharge, and a funnel-shaped discharge emerges at the instantaneous cathode. The spectral line intensity and the corresponding electron excitation temperature all decrease with the distance away from the electrodes, indicating that the plasma state in different positions of the discharge column in the side view of the new type of single filament is different.

[Study on Spectral Characteristics of Micro Plasma Channels of Different Gas-Gap in Dielectric Barrier Discharge].

By optical emission spectrum, we report on the first investigation on the plasma parameters of micro plasma channels which are generated in two gas-gaps with different thickness in a triple-layer dielectric barrier discharge system. Different from the micro plasma channels formed in traditional two-layer dielectric barrier discharge, micro plasma channels formed in the triple-layer dielectric barrier discharge system reflect a unique discharge characteristic. From the pattern images taken by an ordinary camera, it shows that micro plasma channels generated in two discharge gas-gaps discharge with different sizes and light intensities. The micro plasma channels in wide gas-gap are much bigger than those in narrow gas-gap, and their light intensities are obvious stronger. By collecting the emission spectra of N2 second positive band (C3∏u --> B3∏g ) and calculating the relative intensity ratio method of N2 molecular ion line at 391.4 and the N2 molecular line at 394.1, the molecular vibration temperature and the average electron energy of micro plasma channels in two gas-gaps as functions of Argon concentration and applied voltage are investigated, respectively. It is found that the molecular vibration temperature and the average electron energy of micro plasma channels in wide gas-gap are lower than those in narrow gas-gap, and they both decrease with the increasing of the Argon concentration. As the applied voltage increases, micro plasma channels in wide gas-gap vary in a small range on the above two plasma investigations, while those in narrow gas-gap vary obviously. It indicates that micro plasma channels in narrow gas-gap are more sensitive to the applied voltage and they have a wider variation range of electric field than those in wide gas-gap.

[Study on spectral line profile of volume discharge and surface discharge in dielectric barrier discharge].

The volume discharge (VD) and surface discharge (SD) were observed in dielectric barrier discharge with a relatively large discharge gap simultaneously by using a high-speed camera. The variations of the spectral line profiles of VD and SD as a function of the discharge parameters were studied by using optical emission spectra. The changes in the width and shift of Ar I (2P2-->1S5) spectral lines of VD and SD with gas pressure and discharge gap were measured in dielectric barrier discharge in argon. It was found that both the width and shift of SD are bigger than those of VD, indicating that the electron density of SD is higher than that of VD. The width and shift of VD and SD increase with the gas pressure increasing, indicating that the electron density of VD and SD increases with the gas pressure increasing. The width of VD and SD increases with the gas gap d increasing from 3. 8 to 4. 4 mm, reflecting that the electron density of VD and SD increases with d increasing.