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Large-scale plasma plumes downstream of plasma jets are in urgent need from a practical viewpoint. In this Letter, an argon plasma jet with floating electrodes is proposed to produce a large-scale planar plume array. Results indicate that with increasing peak voltage (Vp), the planar plume array elongates gradually and scales up in the lateral direction to an optimal value of 90.0 mm. There is only one discharge pulse per voltage half cycle, whose intensity and duration increase with increasing Vp. Moreover, there is a time lag between the initiations of individual plumes. Fast photography reveals that the planar plume array originates from the repeated process of some micro-discharge filaments stretching along the argon stream. By optical emission spectroscopy, the spatial distribution of plasma parameters is obtained, such as electron density, electron temperature, and gas temperature. At last, the planar plume array is employed to test the surface modification of polyethylene terephthalate, for which a uniform modification has been realized with a scan velocity of 1.0 cm/min. These results are of great significance for the development of large-scale atmospheric pressure plasma sources. [ABSTRACT FROM AUTHOR]

Plasma jet normally operates in a regime of positive or negative streamers. Different propagating behaviors have been investigated for positive streamers. However, there are few studies on negative streamers. In this paper, a two-dimensional fluid model is used to simulate the behavior of a negative streamer encountered with a cloud of positive ions. Simulation results indicate that the negative streamer behaves like a free streamer when the ion cloud has a low charge density. After initiation near the needle tip, the streamer propagates along the axis, passes through the ion cloud, and finally reaches the anode vicinity along a straight line. When the streamer reaches the ion cloud, its head radius (R0) is investigated as a function of parameters, including the voltage amplitude and the gap width, as well as the charge density, axial position, and spatial size of the ion cloud. At a given moment, electric field strength and electron density near the streamer head increase with increasing charge density of the ion cloud. In the case of a high charge-density ion cloud, after a primary streamer propagates some distance along the axis, a positive secondary streamer, and a negative secondary streamer start to propagate from the cloud to the cathode and the anode, respectively. [ABSTRACT FROM AUTHOR]

Compared with the diffuse mode of helium plasma jets, a filamentary mode is normally produced in the plasma plume with less expensive inert gas, such as argon, which is undesirable because intense discharge in the filamentary mode may cause damage to fragile samples. Many efforts have been attempted to realize the diffuse mode of an argon plasma jet. In this paper, the diffuse mode is realized in an atmospheric pressure argon plasma jet with increasing biased voltage (V b) applied to a downstream plate electrode. Results show that the diffuse mode transits from the filamentary mode with the increase of V b. Waveforms of voltage, current and integrated light emission reveal that the filament originates from a positive discharge with a needle anode, while the diffuse mode results from negative discharges with a needle cathode, which consist of a Trichel-pulse phase and a slower-varying phase. By fast photography, the positive discharge is attributed to a streamer regime, whereas the negative discharges belong to a Townsend-discharge regime. From optical emission spectroscopy, electron density, electron excitation temperature, vibrational temperature, and rotational temperature are studied as functions of V b. [ABSTRACT FROM AUTHOR]

Diffuse dielectric barrier discharge was first produced in 3-mm-thick air gap at atmospheric pressure using two plane parallel electrodes each covered by one specific alumina plate with a thickness of 2.3 mm. Based on the discharge photographs of 10 ns exposure time taken with an intensified CCD camera, the diffuse discharge was identified with Townsend discharge. The Townsend breakdown voltage for this 3-mm air gap is about 5.7 kV, significantly lower than 11.2 kV, the streamer breakdown voltage of the air gap. If the alumina plate is too thin, the discharge transits to filamentary discharge. If it is too thick, the discharge is too weak to observe. Thermally stimulated current experiments revealed that there exist more shallow traps in the ceramic than in quartz plate after discharge pretreatment. The uniqueness of the shallow traps in the surface of the specific alumina plate, as well as the effect of the current limitation by dielectric leads to a Townsend discharge. [ABSTRACT FROM PUBLISHER]