Abstract
Pyrolytic graphite serves two functions in a new type of LaB6 cathode; it supports and heats the LaB6 emitter. The high anisotropic resistivity of pyrolytic graphite allows a compact heater‐emitter design a few millimeters in size, and the chemical compatibility of graphite with LaB6 at the operating temperature of about 1500°C prevents any lifetime reducing chemical reactions between the two materials. Typical heating power inputs have been measured to be 15 W at a heating current of about 3 A. One of these LaB6 cathodes has been tested in a demountable vacuum system at an average emission current density of 1.6 A/2cm for over 900 h without signs of impending failure.

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