High-density blue-mode argon plasma under an expanding magnetic field provided by permanent magnets

A 13-cm-diameter magnetically expanding plasma source using only permanent magnets and a high-power radio frequency (RF) generator of 13.56 MHz are installed in the Large diameter Permanent Magnets expanding Plasma machine at I wate University. The source is preliminarily operated for 500-W and 3-kW RF powers of 13.56 MHz in argon of 0.2 Pa. The double concentric arrays of the permanent magnets can provide expanding magnetic fields of about 80 G in the source tube and about 10 G at 30 cm downstream of the source exit. A purple light emission is seen for low-power condition of 500 W, while a blue-mode argon plasma is observed for high-power operation of 3 kW. The blue light emission implies the production of the high-density plasma by helicon mode discharge. In this paper, the images of the plasmas are presented.