ABSTRACT
Low temperature plasma generated by plasma needle in atmospheric pressure air has extensive application prospects in industry because the vacuum device can be dispensable. In the present paper a stable plasma plume was generated in air by using a plasma needle device. The vibrational temperature and gas temperature were investigated for the plasma plume by optical spectroscopic method. Research results show that the plasma plume generated in atmospheric pressure air can be distinguished as a strong emission area near the needle followed by a weak emission area. The light emission signal from the discharge is a pulse per half cycle of the applied voltage with a time width of several microseconds. Results also indicate that the vabrational temperature varies from 2 500 to 3 000 K for different emission locations. The vibrational temperature increases with increasing the distance from the needle point in the strong emission area and it reaches a peak value at a distance of about 5mm from the needle point. The vibrational temperature decreases with increasing the distance from the needle. Similarly, the gas temperature decreases from 640K to 540K with increasing the distance from the needle point. These results are of great importance for the industrial applications of air discharge at atmospheric pressure.
ABSTRACT
A plasma jet of a dielectric barrier discharge in coaxial electrode was used to produce plasma plume in atmospheric pressure argon. Spatially and temporally resolved measurement was carried out by photomultiplier tubes. The light emission signals both from the dielectric barrier discharge and from the plasma plume were analyzed. Furthermore, emission spectrum from the plasma plume was collected by high-resolution optical spectrometer. The emission spectra of OH (A 2sigma + --> X2 II, 307.7-308.9 nm) and the first negative band of N2+ (B2 sigma u+ --> X2 IIg+, 390-391.6 nm) were used to estimate the rotational temperature of the plasma plume by fitting the experimental spectra to the simulated spectra. The rotational temperature obtained is about 443 K by fitting the emission spectrum from the OH, and that from the first negative band of N2+ is about 450 K. The rotational temperatures obtained by the two method are consistent within 5% error band. The gas temperature of the plasma plume at atmospheric pressure was obtained because rotational temperature equals to gas temperature approximately in gas discharge at atmospheric pressure. Results show that gas temperature increases with increasing the applied voltage.
