JPS6367741B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for daring the emitter of a field emission electron gun.

In a field emission type electron gun, a strong electric field is generated at the tip of the emitter to cause electrons to be emitted from the emitter, and a negative accelerating voltage is applied to the emitter to accelerate the emitted electrons. Now, when using such an electron gun, the tip of the emitter is thin at the beginning of use, so the emission current (hereinafter referred to as the emission current) is extremely large, and this emission current increases as the accelerating voltage increases. If the accelerating voltage is suddenly increased, the emitter current increases significantly, causing abnormal phenomena such as the tip of the emitter flying off.

Therefore, set the optimum emission current value that will not cause abnormal phenomena at the tip of the emitter at the final acceleration voltage setting, increase the acceleration voltage, and when the emission current reaches the set value, the original acceleration voltage value ( After returning the temperature to zero (normally zero), a heating current of an appropriate size is passed through the filament holding the emitter for an appropriate length of time to make the tip of the emitter appropriately thick, so-called daring, and then the acceleration voltage is increased again. One possible method is to return the acceleration voltage to the original value when the emission current reaches the set value, and repeat the grinding operation to bring the set acceleration voltage to the set acceleration voltage. Since daring is carried out by passing a heating current through the filament, there is a problem in that the tip of the emitter is easily damaged.

Therefore, the present invention provides a new method in which daring is always performed in an optimal state without relying on the operator's intuition and experience.

The attached drawing is a schematic diagram of a dalling device for an emitter of a field emission electron gun, showing an example of application of the dalling method of the present invention.

In the figure, 1 is an emitter fixed on a filament 2 for holding and heating the emitter. Although not shown, an electrode for generating a strong electric field at the tip of the emitter is arranged below the emitter, and an electrode for accelerating the electrons emitted from the emitter is arranged below the emitter. A DC power supply is inserted between them. 3 is an accelerating voltage power supply inserted between the latter electrode at ground potential and the emitter. 4 is a circuit that generates a heating current for heating the filament 2, which is connected to a central processing unit (hereinafter referred to as CPU) 5 having arithmetic functions, memory functions, etc., via a DA converter 6, a selector 7, and an amplifier 8. A pulse signal having data on the magnitude of the heating current and the time during which the heating current is applied is input. A heating AC power source 9 that forms a heating current generating circuit 4 by this input
The insulating transformer 10 generates a heating current in response to the pulse signal and sends it to the filament 2. The acceleration power supply 3 inserted between the middle point of the secondary side of the isolation transformer and the ground is connected to the CPU 5 which is sent via the DA converter 6, selector 7 and amplifier 11.
It is controlled by the command of Reference numeral 12 denotes an amplifier that captures a signal from the connection point between the accelerating power source 3 and the ground at its positive input terminal. Sent to CPU5. 15 is an amplifier that captures a signal from the connection point of resistors R 1 and R ₂ in the series circuit of resistors R ₁ and R ₂ connected in parallel to the series circuit of the acceleration power supply ₃ and resistor R ₃ to its positive input terminal; Then, a signal corresponding to the acceleration voltage value is sent to the CPU via the selector 13 and the AD converter 14.
Send to 5.

Now, the acceleration voltage value and emission current value to be set to the CPU 5 are input in advance, and the acceleration voltage is increased. At this time, the CPU 5 returns the acceleration voltage to its original value when the emission current becomes equal to the set value. Then, the CPU 5 sends a pulse signal to the power supply 9 of the heating current generation circuit 4 with an amplitude corresponding to the magnitude Id of the heating current to be applied to the filament 2 and a pulse signal having a width corresponding to the time t to be applied to the filament 2. A heating current of magnitude Id flows for a time t. Next, the acceleration voltage is increased again according to a command from the CPU 5, and when the emission current reaches the set value, the acceleration voltage is returned to the original value. And again CPU5
In the same way as above, the CPU issues a command to send a heating current to the filament, but the CPU determines the amount of change in the accelerating voltage from the previous value, that is, the currently set emission. Calculate so that the ratio of the difference between the accelerating voltage value that reached the current and the accelerating voltage value that reached the set emission current in the previous stage and the amount of heating power applied to the filament is below a certain appropriate value in any daring stage. It is set as follows. This appropriate value is
Depending on the amount of heating power applied to the filament, the amount of change in the accelerating voltage with respect to the heating time may become large and cause the emitter to fly off. Therefore, the accelerating voltage with respect to the heating time should be set to such an extent that such an accident will not occur. This value is the amount of change. Applicable
The CPU determines the amplitude and width of the pulse signal so as to have such a ratio value and sends it to the heating current generating circuit 4 during the next daring. Then, the CPU
5 calculates the value of the ratio from the monitored heating current, heating time, and acceleration voltage after daring, determines the heating current and heating time for the next daring, and during that time,
The operation of increasing the accelerating voltage from zero is repeated until the emitter current reaches the set value, and when the accelerating voltage value reaches the set value, daring is completed.

According to such an invention, daring is always automatically performed in an optimal condition without relying on the operator's intuition and experience, so that even an amateur can perform daring of emitters without causing any emitter accidents.

[Brief explanation of drawings]

The attached drawing is a schematic diagram of a dalling device for an emitter of a field emission electron gun, showing an example of application of the dalling method of the present invention. 1: Emitter, 2: Filament, 3: Accelerating voltage source, 4: Heating current generation circuit, 5: Central processing unit (CPU).

Claims (1)

[Claims] 1. A process of increasing the accelerating voltage value applied to the emitter of the field emission electron gun, and returning the accelerating voltage value to the original value when a preset value of emission current flows, and flowing a heating current to the holder of the emitter. In this method, the process is repeated until the accelerating voltage reaches the set value.The preset accelerating voltage value and the set emitter current value are input into a device with arithmetic functions, and the magnitude of the heating current to be passed through the emitter holder is calculated. The time, emission current, and accelerating voltage are monitored and sent to the device with the calculation function, and when the emission current reaches the set value, the amount of change in the accelerating voltage value from that in the previous stage, the heating current value, and the flowing time A method for daring an emitter, characterized in that the value of the heating current or the time of flowing it is controlled so that the ratio of the amount to the amount corresponding to the product of is below a suitable value.