By choosing an appropriate duty cycle and modulation frequency, the pulse-modulated RF discharge can be optimized to provide a high-density atmospheric plasma with a reduced power consumption but without the risk of gas heating in pure helium. In this paper, we presented a fluid model to investigate the generation of reactive oxygen species (ROS) in an atmospheric pulse-modulated RF discharge with He/O 2 mixtures. The numerical results show that modulated by a pulse the electrons could not fully interact with the oxygen molecules, then leading to a less consumption of electrons. Thus, the production of ground state atomic oxygen, excited atomic oxygen and single delta oxygen (SDO) are suppressed, however, due to the reduced power dissipation under pulse modulation, the production of ground state atomic oxygen and excited atomic oxygen are still effective. Consequently, the duty cycle and modulation frequency can also be used to manipulate the generation of ROS in an atmospheric RF discharge.

In this paper, we present a theoretical study on the discharge characteristics of radio-frequency discharges at atmospheric pressure driven by a higher frequency of 40.68 MHz while the electrode gap is altered. Based on the analytical equations and simulation data from a one-dimensional fluid model, an optimal gap between electrodes, at which the largest electron density is obtained, can be observed under a constant power condition; however, as the electrode gap increases the time-averaged electron temperature decreases, and the underpinning physics is also discussed based on the simulation results. This study indicates that at a constant power by choosing an appropriate electrode spacing, the rf discharge can be effectively optimized at atmospheric pressure.