In this paper we present an experimental and computational study on the optimization of pulse-modulated radio-frequency (rf) discharges at atmospheric pressure. Based on the measured and simulated data, to improve the electron density and electron temperature in a pulse-modulated rf discharge, a lower modulation frequency, smaller than 50 kHz, with a higher duty cycle, usually larger than 30%, should be used. But to reduce the power consumption and lower the gas heating, the duty cycle should be smaller than 60%. On the other hand, to achieve a quasi-continuous rf plasma in a whole modulation cycle, a modulation frequency larger than 100 kHz is preferred. Thus, by choosing an appropriate modulation frequency and duty cycle, the pulsed rf discharge can be effectively optimized to produce a high-density and non-equilibrium atmospheric plasma without the risk of gas heating but with a reduced power consumption.

Two kinds of floating electrode, floating dielectric barrier covered electrode (FDBCE) and floating pin electrode (FPE), which can enhance the performance of plasma jet are reported. The intense discharge between the floating electrode and power electrode decreased the voltage to trigger the plasma jet substantially. The transition of plasma bullet from ring shape to disk shape in the high helium concentration region happened when the floating electrode was totally inside the powered ring electrode. The enhanced electric field between propagating plasma bullet and ground electrode is the reason for this transition. The double plasma bullets happened when part of the FDBCE was outside the powered ring electrode, which is attributed to the structure and surface charge of FDBCE. As part of the FPE was outside the powered ring electrode, the return stroke resulted in a single intensified plasma channel between FPE and ground electrode.

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Here we compare the plasma plume propagation characteristics of a 3-channel pulsed RF plasma jet array and those of the same device operated by a pulsed dc source. For the pulsed-RF jet array, numerous long life time ions and metastables accumulated in the plasma channel make the plasma plume respond quickly to applied electric field. Its structure similar as “plasma bullet” is an anode glow indeed. For the pulsed dc plasma jet array, the strong electric field in the vicinity of the tube is the reason for the growing plasma bullet in the launching period. The repulsive forces between the growing plasma bullets result in the divergence of the pulsed dc plasma jet array. Finally, the comparison of 309 nm and 777 nm emissions between these two jet arrays suggests the high chemical activity of pulsed RF plasma jet array.