Double layers in a plasma with negative ions

Summary form only given. The formation of double layers in a plasma containing positive ions, negative ions, and electrons is being investigated. This work is done in a triple plasma device with two independent plasma discharge sources operating in argon at pressure on the order of 10^-5-10^-4 torr. The double layers are produced by applying a potential difference between the two independently produced plasmas. In Ar⁺ /e^- plasmas, the double layers are characterized by potential differences eV/kTe~10-30. The negative ion plasmas are produced by adding small amounts of SF₆ gas into the argon ion/electron plasma. The plasma electrons readily attach to the SF₆ molecules to form a plasma with Ar⁺, e^-, and SF₆^- ions, although other negative ion species as well as additional positive ions may also be present. In one typical case investigated extensively, the addition of SF₆ results in the formation of a potential structure in which the overall potential drop present in the pure Ar⁺/e^- double layer is distributed over two smaller double layers over a more extended axial region