Abstract

The helium and argon have been widely used as discharge gases in atmospheric pressure plasma

jets (APPJs) for bacteria inactivation. The APPJs show apparent different in bullet propagation

speed and bacteria inactivation rate apparently vary with discharge gas species. This work shows

that these two distinctive features of APPJs can be linked through one factor, the metastable

energy level. The effects of helium and argon metastable species on APPJ discharge mechanism

for reactive oxygen nitrogen species (RONS) generation in APPJs are investigated by experiments

and numerical estimation. The discharge mechanism is investigated by using the bullet velocity

from the electric field which is obtained with laser induced fluorescence (LIF) measurement. The

measured electric field also applied on the estimation of RONS generation, as electron energy source

term in numerical particle reaction. The estimated RONS number is verified by comparing NO and

OH densities to the inactivation rate of periodontitis bacteria. The characteristic time for bacteria

inactivation of the helium-APPJ was found to be 1.63 min., which is significantly less than that of

the argon-APPJ, 12.1 min. In argon-APPJ, the argon metastable preserve the energy due to the

lack of the Penning ionization. Thus the surface temperature increase is significantly higher than

helium-APPJ case. It implies that the metastable energy plays important role in both of APPJ

bullet propagation and bacteria inactivation mechanism.

doi:10.3938/jkps.68.1176

https://link.springer.com/article/10.3938/jkps.68.1176