W-ThO2 thermionic cathode activated with nanoscale oxide

A novel tungsten cathode material with nanoscale oxide used in are plasma h as been fabricated by hot-pressing (HP). A comparative study with the conve ntional cathode has been made on microstructure, are starting characteristi cs and cathode spot morphology after arcing. The results show that the micr ostructure, which is completely different from that of the conventional cat hode, consists of tungsten matrix of equiaxed 4-mu m fine grains with homog eneous dopants of ThO2 less than 200 nm. The are starting field for this ca thode is three times lower than that for the conventional electrode. Upon t he are action, the spot of the cathode has been melted weakly. (C) 1999 Els evier Science B.V. All rights reserved.