| 摘要 |
<p>PURPOSE:To uniformly set the operating temperature of three cathodes and improve reliability by setting the heater assembling size of central heater structure to the value smaller than the heater assembling sizes in both sides. CONSTITUTION:The heater assembling size lb of the heater structure 1b at the center is set shorter than the heater assembling size lac of the heater structures 1a, 1c located in both sides and substantial resistance of heater structure 1b at the center is smaller than that of heater structurs 1a, 1c located in both sides. When a voltage is applied to the heater structures 1a, 1b, 1c, a heater current flows equally to the three heater structures. But, since a resistance value of heater structure 1b at the center is smaller than that of the heater structures 1a, 1c in both sides, generation of heat from the heater structure 1b at the center is reduced to a small value. As a result, the operating temperature of cathode 2b at the center which receives the heat by irradiation from both sides can be set equally to the cathodes 2a, 2c.</p> |
