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J. Laimer, S. Haslinger, W. Meissl, J. Hell, H. Störi:
"Glow-like discharges observed in an atmospheric pressure radio-frequency capacitive plasma yet operated with contaminated helium";
in: "Proc. XXVII Int. Conf. on Phenomena in Ionized Gases (ICPIC 2005)", XXVII Int. Conf. on Phenomena in Ionized Gases (ICPIC 2005), Eindhoven/NL, 2005.

An atmospheric pressure plasma jet (APPJ) consisting of two planar electrodes with adjustable gap
spacing was developed. When operated with contaminated helium two distinct operating regimes
were observed. The first one is the 􀀁-mode of an rf discharge, the other one is the 􀀂-mode of an rf
discharge, which can either exist alone or coexist with the 􀀁-mode. At higher gap spacings, first,
the 􀀁-mode covers only a fraction of the electrodes. By increasing the rf power the discharge
spreads across the electrodes until the entire electrodes are covered with a uniform glow. With an
further increase of rf power a transition to a high current density discharge (􀀂-mode) takes place,
which covers only a small fraction of the electrodes. At low gap spacings stable uniform glow-like
discharges (􀀁-mode) occur already immediately after ignition and prevail until an upper power
limit, where a transition to a coexisting 􀀁- and 􀀂-mode takes place. Also in this case the high
current discharge (􀀂-mode) covers only a small fraction of the electrodes, however, the 􀀁-mode
covers the rest of the electrodes. As long as rf power was not increased too quickly, no arcing
occurred.

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