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Q. ul Ain, J. Laimer, H. Störi:
"RF Discharges in Nonequilibrium Atmospheric-Pressure Plasma Jets at Narrow Gap Spacings";
IEEE Transactions on Plasma Science, 40 (2012), 2883 - 2887.

Electrical and spectroscopic investigations of an
atmospheric-pressure plasma jet (APPJ) using variable flow rates
of helium gas have shown that an alteration of the gas flow
rate changes the operation region of stable uniform discharges.
By decreasing the gap spacing to values below 400 μm and
decreasing the gas flow rate, the uniform discharges can be
operated at higher current densities and, consequently, higher
radio-frequency power. Time-resolved optical emission spectroscopy
has shown that, at low gas flow rates in narrow gaps
(below 400 μm), back diffusion is prominent, which influences the
stability of the discharge in the jet. An attempt for scaling up an
APPJ by doubling its surface area has shown that, with increasing
the surface area, the power dissipation cannot be increased, thus
limiting the possibility to scale up such type of plasma sources.
Index Terms-Atmospheric-pressure plasma jet (APPJ), glowlike
discharge, metastable state, Penning ionization, radiofrequency
(RF) discharge, γ-discharge.