Formation of annular plasma downstream by magnetic aperture in the helicon experimental device

• DOI: 10.1063/1.4975665
• Publication Date: 2017-02-01T14:31:03Z
• Authors: Soumen Ghosh; S. Yadav; K. K. Barada; P. K. Chattopadhyay; J. Ghosh; R. Pal; D. Bora
• Keywords: Helicon; Aperture (computer memory); Annulus (botany)

In the Helicon eXperimental (HeX) device, geometric aperture is fixed, but position of magnetic can be varied. Working with Argon gas in pressure range 1 − 10 × 4 mbar, an annular plasma (density ∼ 16 m 3) formed downstream, always front aperture. This occurs irrespective relative or presence a radial electric field. contrary to earlier proposition made by others that field necessary produce hollow profile. Instead, ionization neutrals radially outer region tail electrons, rotating fast due gradient-B drift azimuthal direction, seems account for observed off-axis density peaking present experiment. also explains variation annulus diameter seen here changing input radio frequency power ( 100 800 W ).