Hydrogen arc discharge in magnetic multipole plasma generator with La2O3 doped Mo bulk cathodes

Bulk cathodes with a large emission area are proposed for use in a magnetic multipole ion source of a neutral beam injector. Compared to designs with tungsten (W) filaments, this design simplifies the thermionic cathode replacement procedure. The cathode was tested by causing a hydrogen arc discharge in a rectangular shaped plasma generator (18 x 39 x 20 cm3). The generator had two La2O3 doped Mo(LM) cathodes of disk shape with 10 cm diameter, which were operated in the emission limited region to find the electron emission current density of LM as a function of its temperature. An arc efficiency of the generator estimated from the present data was 1/3 of that typically achieved in ion sources with the W filaments. In the experiment, a few improvements were also made for flattening the distributions of ion saturation current density near a plasma grid of generator and of the cathode temperature. (author)