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The numerical modelling of Joule heating effects in thoriated tungsten cathodes of high-current plasma arcs

2000; Institute of Physics; Volume: 33; Issue: 11 Linguagem: Inglês

10.1088/0022-3727/33/11/313

1361-6463

E. Casado, V. Colomer,

Metal and Thin Film Mechanics

The influence of the Joule heating on the performance of thoriated tungsten cathodes working at current densities of 103-104 A cm-2 is investigated. The variation of the degree of coverage of the cathode surface by thorium atoms is considered, together with the heat conduction and the diffusion of thorium in the cathode bulk. The nonlinear system of equations governing these processes is solved numerically and the time evolution of the spot temperature is obtained. The effects of different working conditions on the cathode lifetime are discussed. It is found that a critical current density exists for which the service time of the cathode has a minimum. It is shown that a small increment in the cathode cooling temperature significantly increases the cathode lifetime.