Large area multi-filamentary plasma source for large volume plasma device-upgrade

This paper discusses the salient features and plasma performance of the newly installed Large Area Multi-Filamentary Plasma Source (LAMPS) in large volume plasma device-upgrade. The plasma source is designed to exhibit a plasma electron density of ∼10¹⁸ m^-3, low electron temperature (∼eV), and a uniform plasma cross section of 2.54 m². The directly heated LAMPS emits accelerated primary energetic electrons when it is biased with a negative discharge voltage with respect to the anode. The hairpin shaped tungsten (W) filaments, each of diameter 0.5 mm and length 180 mm, are heated to a temperature of 2700 K by feeding ∼19.5A to each filament. The LAMPS consists of 162 numbers of filaments, and it has been successfully operated with a total investment of 50 kW of electrical power. The LAMPS as a laboratory plasma source is characterized by large operational life, ease of handling, better compatibility to high pressure conditions, and advantages over other contemporary plasma sources, viz., oxide coated cathodes, RF based sources, and helicon sources, when producing plasma over large cross sections and fill volumes. Pulsed argon plasma is produced with quiescence (δn_en_e≪1%) using LAMPS for the duration of 50 ms and a reasonably good radial uniformity (L_n = 210 cm) is achieved. Good axial uniformity is also observed over the entire length of the device. Initial measurements on plasma parameters have yielded plasma density of ∼2×10¹⁷m^-3 with existing set of filaments. A plasma density of ∼10¹⁸ m^-3 is envisaged for larger thickness of filaments, such as 0.75 and 1.0 mm, with the existing plasma source assembly setup.