| 摘要 |
PROBLEM TO BE SOLVED: To realize a focus shape and focus size on a target as designed. SOLUTION: A heating element 10 is composed of a pair of current-carrying terminals 12, 14, a pair of leg parts 16, 18 and an emitter support part 20. A slot 22 (recessed part) is formed on the upper surface of the emitter support part 20. The slot 22 is provided with a pair of sidewalls and a flat bottom face. A thermoelectron emitter 24 is embedded in an embedding recessed part of the bottom face. The surface of the thermoelectron emitter 24 is exposed to part of the bottom face, and the exposed surface is flush with the bottom face. The electron flow, emitted from the exposed surface of the thermoelectron emitter 24, converges by an electric field formed by the sidewalls of the recessed part 22.
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