Operation of a permanent-magnets- expanding 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 13.56 MHz for plasma production is maintained at 200 W and an expanding magnetic field of about 200 G 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.