Temporal and spatial resolved optical emission behaviors of a cold atmospheric pressure plasma jet

Abstract

The propagation behavior of cold atmospheric pressure plasma jets has recently attracted lots of attention. In this paper, a cold He plasma jet generated by a single plasma electrode jet device is studied. The spatial-temporal resolved optical emission spectroscopy measurements are presented. It is found that the emission intensity of the He 706.5 nm line of the plasma behaves similarly both inside the syringe and in the surrounding air (plasma plume). It decreases monotonously, which is different from the emission lines, such as N2 337.1 nm line, N2+ 391.4 nm line, and O 777.3 nm line. For the discharge inside the syringe, the emission intensity of the He 706.5 nm line decays more rapidly than that of the other three spectral lines mentioned above. The N2 337.1 nm line behaves a similar time evolution with the discharge current. For the N2+ 391.4 nm line and the atomic O 777.3 nm line, both of them decay slower than that of the He 706.5 nm and the N2 337.1 nm. When the plasma plume propagates further away from the nozzle, the temporal behaviors of the emission intensities of the four lines tend to be similar gradually. Besides, it is found that, when the size of the plasma bullet appears biggest, the propagation velocity of the bullet achieves its highest value while the emission intensity of the N2+ 391.4 nm line reaches its maximum. Detailed analysis shows that the Penning effect between the metastable state Hem and the air molecules may play a significant role in the propagation of the plasma bullet in the open air.

Operation modes of the helium dielectric barrier discharge for soft ionization

“…excited helium atoms (He ⁎ , including helium metastables He M ) and ions (He + , He 2 + ). As shown by time-resolved measurements reported by Xiong et al [21], the excited N 2 + are present in this "dark" period between two discharge pulses when plasma is generated in helium. As pointed out in that work, this is most probably due to Penning ionization involving the helium metastables and ground-state nitrogen molecules:…”

“…However, the jet is axially symmetric and its non-homogeneity along the axis of penetration is well defined. By combining experimental findings with time-resolved measurements on a helium DBD plasma jet reported by Xiong et al [21], it can be argued that the main excitation path leading to protonation of water in helium plasma jet penetrating in the air atmosphere starts with collisions between helium metastable atoms and nitrogen molecules in the air. Finally, we agree with Xiong et al [21] that Penning ionization of nitrogen molecules and subsequent energy transfer to the water molecules are the processes leading to an efficient water ionization and protonation.…”

Propagation Phases of Plasma Bullets

“…The LTPJs are usually operated at atmospheric pressures, and they generate chemically rich gas-phase environments around room temperature [4]- [6]. These properties of the LTPJs led to their extensive use in material processing and biomedical applications.…”

Comparison of the characteristics of atmospheric pressure plasma jets using different working gases and applications to plasma-cancer cell interactions

“…Furthermore, the local electric field is proportional to the charges carried by the bullet. 41 When more gas molecules are ionized, a stronger local electric field is induced in front of we have an ordering of υ He > υ N2 > υ Ar, because T e is not much changed in different discharges (although we have a general scaling as α He > α Ar > α N2 , the effects of μ + and υ d are stronger). This argument is in agreement with the observed plume lengths (L) in the order of L He > L N2 > L Ar shown in Fig.…”