Local Heating of Point Cathode: Numerical Calculations of Temperature Distribution and Cathode Shape Variation by Evaporation

Abstract

When the tip of a point cathode is locally heated by a laser or electron beam irradiation to a high temperature below the melting point, the cathode can be operated at a fairly high emission current density for a long period of time because the cathode evaporation is locally confined to the tip. The temperature distribution and the shape variation of a straightened tungsten wire cathode are examined with a numerical method under different heating conditions. When a portion of the cornical tip of the cathode is kept at a constant high temperature, evaporation occurs from the cone apex, although the portion is near the cone base. During evaporation, the tip maintains a conical shape, and the apex temperature is nearly constant. The same results are obtained when an incident beat energy is given in a large area of the cathode tip. There are large allowances in the heating position and area, which promise a long lifetime of the cathode. Numerical method and results are described