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Summary: The APPJ is the subject of intensive recent research. Basically, the APPJ consists of an atmospheric‐pressure RF discharge between two bare metallic electrodes and of a superimposed gas flow consisting predominantly of a rare gas. In its usual operating regime, a uniform glow discharge, which was identified as the α mode of a RF discharge, can be sustained over a wide range of gap spacings and RF powers. Maximum electron densities of 0.22 × 1012 cm−3 were assessed for helium and of 2.75 × 1012 cm−3 for argon by evaluation of electric measurements using a simple equivalent circuit model. At low RF powers, only partial coverage of the electrodes was observed. At high RF powers, a breakdown of the α sheath occurred, and a transition to either a pure γ mode or a coexisting α and γ mode took place. The γ mode covers only a small fraction of the electrode surface. In helium, it was easy to ignite directly a pure α discharge, but not in argon. Due to the high over‐voltage needed, the ignition in argon mostly led to a coexisting α and γ mode. However, through RF power reduction a transition to a pure α discharge can be initiated.

Recently, there has been increased interest in using atmospheric pressure plasmas for materials processing, since these plasmas do not require expensive vacuum systems. However, APGDs face instabilities. Therefore, special plasma sources have been developed to overcome this obstacle, which make use of DC, pulsed DC and AC ranging from mains frequency to RF. Recently, the APPJ was introduced, which features an α‐mode of an RF discharge between two bare metallic electrodes. Basically, three different geometric configurations have been developed. A characterization of the APPJs and their applications is presented.

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