| 摘要 |
PURPOSE:To enable both the variation of the output of a cathode-heating power source and the temperature variation of a cathode which is caused by external disturbance to be reduced in any case, in which a tungsten filament or a directly heated LaBe cathode is used as the cathode, by a simple work of connecting a resistor to the output of the cathode-heating power source according to the cathode used. CONSTITUTION:When a directly heated LaBe cathode or the like is used, a switch 10 is turned off so that a resistor 9 is not included in a circuit. Such condition is indicated by the equivalent circuit in the figure. In the figure, the symbol 12 represents a constant-current-type power source 13 used for heating the cathode, the symbol 13 represents the resistance of the directly heated LaBe cathode, and the temperature variation of the cathode is reduced. However, when a tungsten filament is used as a cathode in this constitution, the temperature variation of the cathode is increased since the resistance temperature coefficient of the tungsten filament is positive. Therefore, in such a case, the switch 10 is turned on so that the resistor 9 is included in the circuit. |
