Characterization of electron extraction from a 40.68 MHz radiofrequency inductive plasma source

An electron current is extracted from a 40.68 MHz inductively coupled plasma source, in which a grounded ion collector electrode is installed to maintain the charge neutrality, by applying a positive voltage to a metallic plate located downstream of the source. The ion collector has an exit orifice of either 20 mm or 2.2 mm in diameter, showing a larger electron extraction current for the 2.2-mm-diameter case. The result is discussed with a global model, implying a higher plasma density for the 2.2-mm-diameter case due to the increased neutral pressure in the source. Metallic and insulator exit having the 2.2-mm-diameter orifice are tested, providing a larger electron extraction current for the metallic case despite a small fraction of a change in the total ion collection area. It is speculated that the electron extraction current is affected by the ion collection near the electron extraction hole and the potential distribution.