Comparison between Uramoto type and straight filament type sheet plasmas as a volume produced H- ion source, (1)

The Uramoto type sheet plasma (transformed from a cylindrical plasma by two permanent magnets) and a long straight filament cathode type sheet plasma are compared as volume produced H- ion sources. For a same discharge power (for example 5 A x 100 V = 500 W), a H- ion current density (2.5 mA/cm2) extracted from the Uramoto type sheet plasma, is above 20 times larger than that from the straight filament type (0.125 mA/cm2). As an essential difference between the two types, it is pointed out that the Uramoto type uses in combination of negative bias voltage on the metalic large vacuum chamber (surrounding the sheet plasma) and a cusp magnetic field produced by the two permanent magnets which are effective on the confinement of electrons and H- ions. A pressure gradient discharge of the ordinary Uramoto type is not essential for volume production of H- ions, but is very useful to reduce the optimum pressure. (author)