[Zurück]

J. Laimer, S. Haslinger, W. Meissl, J. Hell, H. Störi:
"Atmospheric pressure radio-frequency capacitive plasma jet operated with argon";
in: "17th Int. Symp. on Plasma Chemistry (ISPC17)", ISPC, 2005, S. 238 - 239.

Today, non-equilibrium atmospheric pressure plasmas attract more and more attention. They can be realized by a
variety of techniques, one of them is the atmospheric pressure plasma jet (APPJ), which was introduced a few
years ago by Selwyn et al. [1-3]. The APPJ operates in a capacitively coupled configuration using rf power and
produces a stable glow-like discharge without dielectric material between the electrodes. Usually it is operated
with a high gas flow of pure helium or helium with addition of reactive gases in the range of a few percent. The
gas flow out of the discharge has a relatively low gas kinetic temperature. Due to recombination the effluent
consists only of neutral species, including metastable species and radicals (in case of reactive gas addition).
Some applications in materials processing and decontamination have been already investigated [4,5]. Recently,
Wang et al. claimed that they are able to operate an APPJ with argon as well [6]. However, they used a
configuration with concentric electrodes.
Very recently we developed an APPJ with planar electrodes featuring a rectangular cross section of the effluent
[7]. The exit of the used APPJ has a width of approximately 50 mm and a gap spacing, which can be adjusted
between 0.5 mm and 2.5 mm in steps of 0.5 mm. Tests with contaminated helium showed that the APPJ can be
operated in a rather uniform glow-like mode within certain limits. This mode was identified as the α-mode of an
rf discharge. However, at the upper limit of this mode a transition to the γ-mode occurred. This high current
density mode covered the electrodes only partially. This type of transition is well known for capacitively coupled
rf discharges at moderate pressures [8], however, for APPJs the transition at the high power limit of the α-mode
was often attributed to arcing.
A scheme of the discharge and the experimental setup is shown in Fig. 1. As a detailed description is given
elsewhere [7], only details specific for the present experiment are given here. The APPJ was operated with argon
(purity 99.999%) at a gas flow rate of 2 slm and rf powers of up to 260 W. The ambient pressure in Vienna is in
average roughly 960 hPa. The electrical properties of the discharge were studied by measuring voltage and
current simultaneously. Pictures of the discharge were taken with a digital camera.

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