Positive- and negative-pulsed argon plasma plumes in the open air

Cold atmospheric pressure plasma plumes have obtained great interests for their attractive features and application potentials. In this work, cold argon plasma plumes were generated in the open air by a single medical-needle excited by a high-power pulsed excitation source. Characteristic comparision was carried out in the plasmas under different polarties of applied voltages. The results showed that the positive pulsed plasma plume performed a larger discharge current and stronger optical emission than the negative case. Gas temperature of the plasmas were obtained by the Boltzmann plot method and fitting the syntheric-to-experimental spectrum of the OH (A-X) transition emission bands. It is found that both the positive and negative pulsed plasma plumes are under a relative low gas temperature about 400 K. Through the high-speed imaging, an interesting propagation process was observed for the positive pulsed plasma plume, during which the plasma first propagates in the form of plasma ‘bullets’, and then transits into typical stream propagation as soon as the ‘bullets’ disappears in the open air, which is much different with the negative case

Propagation dynamics of a room-temperature pulsed argon plasma plume through a simple dispersion-grating diagnostic method

In this paper, a novel grating-ICCD camera dispersion diagnostic method was designed to investigate the propagation behaviors of an open-air pulsed argon plasma plume. Based on the dispersion feature of gratings, the irradiative plasma plume was dispersed into several emission-volumes corresponding to different wavelengths. And a series of high-speed dispersed emission-image sequences were captured by the ICCD camera. From these sub-microsecond emission-images at different wavelengths, the temporal and spatial propagation behaviors of excited species in the plasma plume were observed clearly

Shadows and photon spheres with spherical accretions in the four-dimensional Gauss-Bonnet black hole

We investigate the shadows and photon spheres of the four-dimensional Gauss-Bonnet black hole with the static and infalling spherical accretions. We show that for both cases, the shadow and photon sphere are always present. The radii of the shadow and photon sphere are independent of the profiles of accretion for a fixed Gauss-Bonnet constant, implying that the shadow is a signature of the spacetime geometry and it is hardly influenced by accretion in this case. Because of the Doppler effect, the shadow of the infalling accretion is found to be darker than that of the static one. We also investigate the effect of the Gauss-Bonnet constant on the shadow and photon sphere, and find that the larger the Gauss-Bonnet constant is, the smaller the radii of the shadow and photon sphere will be. In particular, the observed specific intensity increases with the increasing of the Gauss-Bonnet constant.Comment: published versio

A branching streamer propagation argon plasma plume

Cold atmospheric-pressure plasma plumes have obtained great interests for their attractive features and application potentials. In this paper, a pulsed argon plasma plume was generated in the open air. Characteristic propagation of the argon plasma plume was carried out through high-speed imaging by an ICCD camera. An interesting propagation process was observed for the plasma plume, during which the plasma first propagated in a single streamer channel, and then with side branching as the applied voltage increased. The side branches are generated surrounding the main plasma channel but not split from the anode tip. This branching streamer propagation behavior was much different from the bulletlike development of typical plasma jets or streamers in point-wire or point-plane gaps