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It is well accepted that increasing the frequency and reducing the electrode gap are effective ways to enhance the discharge stability in atmospheric radio-frequency (rf) discharges. In this paper, we explore a 1-D fluid model to investigate the discharge characteristics when the \alpha-\gamma mode transition occurs. The differential equation satisfied at the \alpha-\gamma mode transition point is given based on the governing equations. From the theoretical analysis and computational data, with an increase in the electrode gap, the power density coupled to the plasmas decreases, and the critical electron density modestly increases at the transition point; the electron temperature both in the sheath and bulk plasma decreases as the sheath shrinks. On the other side, as the frequency is raised, just at the mode transition point, the applied voltage reduces, and the plasma density increases almost exponentially with a higher electron temperature in the sheath. From the view point of application, the discharge driven by a high frequency at a narrow gap is desirable to produce a stable and high-density atmospheric plasma with a large power density coupled. [ABSTRACT FROM PUBLISHER]

The plume of a cathodic arc operated in atmospheric pressure gas is examined using an intensified camera and a spectrograph. A 0.2-J pulse arc is shown to generate a glowing jet $\approx 10$ mm in extent. Images recorded in the first microseconds after ignition show that the jet has a smaller core \approx 2$ mm in length. A spatially resolved Stark broadening measurement is performed along the jet core. The measured electron density is 1– 2 \times 10^{20} \text{m}^{\vphantom {R^{R}}-3} . A model for the cathodic arc plasma–gas interaction is presented. The obtained equilibrium between the forward and reverse charge exchange processes is suggested as enabling the extended jet core. [ABSTRACT FROM PUBLISHER]

A 1-D self-consistent fluid model was employed to investigate the effect of driving frequency on the discharge characters of a dielectric barrier discharge at atmospheric pressure in argon excited by a periodic Gaussian voltage. The simulation results indicate that there are two discharge modes: 1) Townsend and 2) glow modes in the multipulse discharge and different transitions between them during the discharge take place with the increase in driving frequency. When the driving frequency is 1 kHz, there is a tendency of transition from the Townsend mode through glow and finally back to the Townsend one during the positive half-circle of applied Gaussian voltage. However, the discharge in the half-circle can all along operate in the glow mode with the higher driving frequency. Moreover, when the driving frequency is sufficiently high, there are also distinct fluctuations of spatial performance of the charge densities in the positive column during the glow discharge. This is caused by the fact that a lot of charged particles created in the gas gap have not enough time to drift and diffuse to the dielectric barriers, and then these particles are preserved in the local discharge gap at such a high frequency. A comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increase in the driving frequency can enhance the plasma chemistry and also expand its volume. [ABSTRACT FROM AUTHOR]