Q-Machine Cathode Producing Large Radial Electric Fields

A segmented cathode, consisting of two insulated concentric tantalum plates, is described. The tantalum sections are heated by radiation from a tungsten back plate, which in turn is heated by electron bombardment. The insulating material is alumina (Al2O3), which is effective up to 2100 K. Arbitrary voltage may be applied across the gap between the concentric front sections. When used as the hot end plate in a Q machine, this cathode maintains large radial electric fields in the plasma interior.