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J. Laimer, H. Reicher, Q. ul Ain:
"Dielectric barrier-free atmospheric pressure radio-frequency glow discharges in narrow gaps";
Poster: XXIX International Conference on Phenomena in Ionized Gases (ICPIG 2009), Cancun/Mexico; 12.07.2009 - 17.07.2009; in: "Proceedings of XXIX International Conference on Phenomena in Ionized Gases (ICPIG 2009)", Ed. A. Juarez-Reyes, (2009), Paper-Nr. PA10-12, 3 S.

At atmospheric pressure uniform radio-frequency (RF) glow discharges can be sustained in helium
down to a gap spacing of at least 100 É m. Such uniform discharges are usually attributed to the
alpha (£\) mode of an RF discharge. While at gap spacings down to 200 É m an ignition of a
gamma (£^) discharge and hence a transition to a coexisting £\ and £^ mode took place already at
relatively low RF powers (> 60 W in the present set-up), at a gap spacing of 100 É m such a
behavior was not observed. At this very narrow gap it was possible to sustain a uniform discharge
up to at least 600 W, most probably due to the absence of a bulk plasma region and a fully
developed £\ sheath, thus inhibiting the £\ sheath breakdown.