Slit extraction type compact microwave ion source

Abstract

A new compact microwave ion source with three antennas has been constructed; it has a large plasma production chamber (16 × 66 × 5 mm 3) for increasing the extraction of ion current by a slit extraction electrode. Even in such a large plasma production chamber, the axial magnetic field (about 900 G) was formed uniformly with a combination of permanent CoSm magnets and ferromagnetic material. The microwave power was fed through coaxial lines. This gives the ion source a flexibility, lacking in the conventional microwave ion source with a rigid wave guide. The compact ion source has no hot filament and can ionize chemically reactive gases. The basic operational characteristics of the ion source and the shape of the extracted ion beam were investigated. About 80% of the supplied microwave power (2.54 GHz, 100 W) was absorbed without any microwave interference from others, producing a dense plasma of 10 12 cm −3. Argon ions of 12.5 mA, nitrogen ions of 13.5 mA, and oxygen ions of 5.6 mA were obtained without mass-separation at an extraction voltage of 20–23 kV at a plasma production chamber gas pressure of 1−2 × 10 −2 Torr.