Operation of a permanent-magnetsexpanding plasma source connected to a large-volume diffusion chamber

A 6.6 cm-inner-diameter permanent-magnets-expanding plasma source is connected to a large-volume diffusion chamber of about 76 cm diameter and 100 cm length, and is operated over a range of 20-300 mPa argon gas pressures. An rf power of 13.56MHz for plasma production is maintained at 200W and an expanding magnetic field of about 200G in the source is provided by permanent magnet arrays. A potential drop of a few tens of volts is observed; a supersonic ion beam with energy corresponding to the potential drop is detected in the diffusion chamber. Radial investigation of the ion beam in the diffusion chamber indicates a detachment of the ion beam from the expanding magnetic field lines provided by the permanent magnets, at about several centimetres downstream of the source exit.