Gliding Arc in Noble Gases Under Normal and Hypergravity Conditions

Abstract

Abstract-This paper describes the gliding arc operated in four different noble gases (helium, neon, argon, and krypton) under normal gravity and hypergravity conditions up to 18 g. We studied the influence of gas flow, gas properties, and gravity-dependent buoyancy on the gliding arc behavior.Index Terms-Atmospheric-pressure plasma, buoyancy, gas flow, gravity. GLIDING arc (GA) [1] has been studied for decades, as it is not only a scientifically compelling demonstration of dynamic plasma phenomena, but also a useful plasma source for many applications [2]. In these, the GA is typically operated in air at atmospheric pressure. However, less attention has been paid to the GAs in noble gases.A typical feature of the GA is its movement along slanted electrodes. The discharge ignites at the shortest distance between the electrodes, then moves upward and finally at maximum elongation it extinguishes owing to insufficient power. The upward movement is due to two phenomena: 1) the GA can be dragged up with upstream gas flow and 2) a thermal buoyancy caused by the difference in mass density between the heated plasma column and the cold surrounding atmosphere is also directed upward. In case of a low or zero gas flow, the buoyancy can be the dominant force moving the GA. As the buoyancy is naturally related to the gas mass density, it increases with rising atomic mass of the used gas and the gravity level.The effect of gravity on plasmas has been investigated before [3], but to our best knowledge, nobody has studied the GA in hypergravity which tends to emphasize the thermal buoyancy over the gas flow. We did so, using Large Diameter Centrifuge (LDC) [4] in ESA/ESTEC facility in the range of 1 g-18 g. We used nearly quarter-elliptic copper electrodes with a minimum distance of 4.5 mm and an initial angle between them of 36°[5], [6]. These electrodes were connected to a current limiting high-voltage transformer supplying 0-10 kV at 50 Hz ac. The configuration was enclosed in a nonconductive discharge chamber with 2 dm 3 inner volume. Front and back walls were made of a heat-resistant glass allowing direct optical observation by digital cameras (Nikon D3100, Canon Power Shot A460). Four noble gases-He, Ne, Ar, and Kr-were selected to cover a wide range of gas mass densities. Their atomic masses are 4, 20, 40, and 84 a.m.u., respectively, giving the mass ratios 1:5:10:21.Long exposure images of the GAs in four noble gases at 1 g are shown in Fig. 1. The gas flow and discharge voltage are slightly different for each gas to maintain stable gliding movement of the arc. Operating in ac, the arc filament periodically brightens and dims, which in combination with upward motion, forms a typical striped structure in the images. This allows a direct visualization of spatiotemporal GA evolution with 10 ms time intervals. The main difference in operation of the GA in different noble gases is, besides the apparent color due to dominant spectral lines, the minimum gas flow needed for the arc to glide (0.4 slm for He, 0.15 slm for Ne, and...

Comparing efficiencies of polypropylene treatment by atmospheric pressure plasma jets

“…The PP treatment was carried out using a set frequency of 21 kHz and varied power (200, 300, 400, and 500 W), the distance between the sample surface and the PT-RPJ nozzle (10, 20, and 30 mm) and the number of passes (1, 2, or 4). During the plasma diagnostics, the influence of the driving switching frequency (16,21,26, and 31 kHz) was also monitored. The experimental configuration of RF-PSJ and ST-GA were described in detail in previous publications.…”

“…In all the studied conditions, the plasma treatment by PT-RPJ increased the PP wettability (Figure 2). The static contact angle (SCA) decreased from (101 ± 2)°of untreated PP up to a minimum of ∘ (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) achieved for the PP samples placed at the 5 or 10 mm distance from the nozzle and treated using one or two passes. The efficiency of the PT-RPJ treatment fell off after increasing the passes to three or the sample-tonozzle distance to 20 mm; the maximum SCA of plasmatreated PP was ∘ (77 ± 2) .…”

“…[20] The arc-based transitional plasma jets start as an arc discharge in the LTE that is cooled down by gas flow into a nonthermal plasma. They can operate in both noble gases [21] and in air, [22][23][24] the second option is more suited for industrial applications. Commercial plasma sources from several different companies (e.g., Plasmatreat, AFS, SurfaceTreat, or Ahlbrand) are already available in the market and have been used to treat synthetic polymers.…”

“…[22][23][24][25][26] A specific type of arc-based plasma jet composed of the filaments evolving along the diverging electrodes is called a gliding arc. [21,24,27] While judging the efficiency of plasma treatment by changes in polymer's wettability and functional group concentration is straightforward, its effects on the adhesion between a polymer and an adhesive are more complicated, with less clear dependabilities. For example, Mandolfino et al [9,28] used a low-pressure plasma treatment to increase the adhesion between PP and twocomponent epoxy glue.…”

Experimental study of gliding arc plasma channel motion: buoyancy and gas flow phenomena under normal and hypergravity conditions

“…Recently, we performed several experiments [37][38][39][40] with gliding arc discharge at the centrifuge, which simulated the hypergravity conditions up to 18g and thus allowed us to study gliding arc in buoyancy dominated regime. The first results proved the strong influence of increased gravity on the plasma channel, such as higher frequency of gliding and lower maximum height reached by plasma.…”