Gas–plasma interactions in a filtered cathodic arc

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Abstract
The physical interactions between the metal plasma beam of a filtered cathodic arc and noble gases introduced into the beam path are studied. Langmuir probe measurements show that the ion saturation current increases rapidly and nonlinearly with pressure until a cutoff point, after which there is a general decrease with a reproducible fine structure in the form of subsidiary maxima and minima. For helium, the electron density increases exponentially by two orders of magnitude, as the pressure rises from base pressure. Electron collisions are believed to be the dominant cause of gas ionization. A theory is proposed to explain these measurements which predicts under special conditions an exponential increase in ion density. The fine structure may have its origin in the so called ‘‘ionization instabilities.’’ Gas ion currents of up to 2 A have been measured showing that the cathodic arc may be useful as a source of gas ions for assisting film deposition.

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