| 摘要 |
PURPOSE:To extend the life of the cathode in the title, even in a high current density operation of 2A/cm<2> or more by constituting a radiating material layer from a second layer consisting of at least one of rare earth metal oxide, rare earth metal, heat resisting metal oxide and heatresisting metal which is formed on a first layer, and a third layer formed on the second layer. CONSTITUTION:An electron radiating material layer 2a is formed of three layers. A first layer 4 is formed on a base 1, and mainly contains alkali earth metals containing barium. A second layer 5 is formed on the first layer 4, and consists of at least one kind of rare earth metal oxide, rare earth metal, heatresisting metal oxide and heat-resisting metal. A third layer 6 is formed on the second layer 5, and mainly contains an alkali earth metal oxide containing barium. As the first layer is uneven, the film of the second layer is formed from near the base to near the surface of the electron radiating material layer. On the other hand, barium evaporated during the operation is stuck to the second surface to increase conductivity; so that the resistance of the whole electron radiating material layer and thus the generation of Joule heat are reduced. |
