Reactive oxygen and nitrogen species (RONS) produced by repetitive pulses in atmospheric pressure plasma jets

Abstract

Summary form only given. Reactive oxygen and nitrogen species (RONS) are desired in numerous applications from the destruction of harmful proteins and bacteria for sterilization in the medical field to taking advantage of the metastable characteristics of O2(1 Δ) to transfer energy to other species. Advances in atmospheric pressure plasma jets in recent years have shown the possibility of using this technology as a source of RONS. The plasma jets consist of small diameter tubes (a few mm) through which rare gas mixtures (e.g., He seeded with a few percent of O2) are flowed into room air. They are typically operated in a dielectric barrier discharge (DBD) configuration which produces an ionization wave (or plasma bullet) with repetition rates of many kHz to tens or hundreds of MHz. In this paper, we report on results of a computational investigation of the production of RONS from repetitively pulsed plasma jets at frequencies from many kHz to many MHz consisting of He/O2 mixtures discharged into ambient air. The computer model used in this study, nonPDPSIM, solves transport equations for charged and neutral species, Poisson's equation for the electric potential, the electron energy conservation equation for the electron temperature, and Navier-Stokes equations for the neutral gas flow. Rate coefficients and transport coefficients for the bulk plasma are obtained from local solutions of Boltzmann's equation for the electron energy distribution. The length of the interpulse period has significant effects on the density and distribution of the RONS in the effluent of the plasma jet. At high repetition rates (producing interpulse periods shorter than the gas clearing time), there is accumulation of RONS in the plume on a pulse-to-pulse basis, enabling further reactions between these species. The ionization wave of the following pulse samples the reactive environment produced by the previous pulse. At lower repetition rates, the interpulse periods are commensurate or longer than the clearing time of the gas through the device. In these cases, the ionization wave enters a more pristine and controllable environment.