JPS58161234A - Field emission type charged particle generator - Google Patents

Abstract

PURPOSE:To prevent an emitter electrode from damaging attributable to an accident by vacuum discharge, by adding in parallel with a pickup electrode the parallel circuit of a resistor and a condenser connected to a diode in series, between the emitter electrode and the pickup electrode. CONSTITUTION:A condenser 11, a diode 12 and a resistor 13 are connected to the side of a high tension power source, while a circuit connecting the condenser 11 to the resistor 13 in parallel is connected to between an emitter 3 and a pickup electrode 4 by connecting the diode 12 in series. With this, in time of vacuum dielectric breakdown between the pickup electrode 4 and an anode 5, excessive voltage being impressed to between the emitter 3 and the pickup electrode 4 can be checked, and likewise in time of vacuum discharge between the emitter 3 and the pickup electrode 4, damage by the vacuum discharge of the emitter can be prevented without degrading a vacuum in vain.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a high acceleration voltage electron gun such as a field emission type electron gun,
The present invention also relates to a field emission type emitter protection circuit that protects an emitter of an ion gun or the like from vacuum discharge.

The configuration of a conventional field emission type electron gun is shown in FIG.

In the figure, reference numeral 1 represents an electron gun chamber kept in vacuum, and the chamber includes an emitter 3 attached to a heating filament 2, an extraction electrode 4 for applying a strong electric field to the tip of the emitter 3, and an anode 5 kept at ground potential. Each of these electrodes is connected to a power supply section 10 by an insulated cable 6. The power supply section 10 includes an accelerating power supply 7 for applying a high potential of about (-) several + KV to the emitter 3, and an extraction power supply for providing a potential difference of about several tens of KV to perform field emission between the emitter 3 and the extraction electrode 4. 8,
and a filament heating power source 9.

In the above configuration, in normal operation, an extraction voltage of several tens of KV is applied between the emitter 3 and the extraction voltage tfi4 to perform field emission, and also between the emitter 3 and the extraction voltage tfi4.
A voltage of several tens of kilovolts (-) is applied between the poles (ground electrodes) 5 as an accelerating voltage for accelerating the field-emitted electron beam.

On the other hand, vacuum dielectric breakdown may occur due to some reason during operation, such as a decrease in the vacancy of the electron gun chamber 1, minute protrusions on each electrode, or residual minute particles in the electron gun chamber. . This vacuum breakdown is caused by the extraction voltage (e.g. 5K
Since the accelerating voltage (for example, 50 KV) is higher than V), a large amount of oxidation occurs between the extraction electrode 4 and the anode 5 to which a high voltage is applied.

When vacuum dielectric breakdown occurs between the extraction electrode 4 and the anode 5 and a vacuum discharge occurs, the extraction electrode 4 momentarily becomes ground potential, and since the extraction power source 8 has internal impedance, there is a gap between the emitter 3 and the extraction electrode 4. Then, a high voltage of several tens of kilovolts, which is an accelerating voltage, is applied transiently, and an excessive voltage that exceeds the allowable value is applied between the emitter 3 and the extraction electrode 4.

By the way, the radius of curvature of the tip of the emitter 3 is approximately 100
Since the emitter 3 is extremely small, this excessive voltage increases the emission current from the emitter 3, and the tip of the emitter 3 evaporates due to dicol heat generation, causing an arc discharge and deforming the tip to a diameter of about 10 μm, which causes the electric field to rise again. It becomes unusable as a emission type emitter.

The present invention was made in view of these points, and includes an emitter, an extraction electrode for forming a strong electric field necessary for field emission of charged particles near the tip of the emitter, and an extraction electrode for forming a strong electric field necessary for field emission of charged particles near the tip of the emitter, An accelerating electrode for accelerating charged particles, the emitter and an extraction electric current l! In a device having an acceleration power source that supplies an extraction voltage between I and an acceleration power source that supplies an acceleration voltage between the emitter and the acceleration electrode, a parallel circuit of a resistor connected in series with a diode and a capacitor is used. By adding it in parallel to the extraction power supply,
This prevents damage to the emitter even in the case of vacuum discharge.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a schematic diagram showing an embodiment of the present invention. 1st
Components that are the same as those in the figures are given the same numbers and their explanations will be omitted. In the figure, a capacitor 11, a diode 12, and a resistor 13 are connected to the electric mff10, that is, the high-voltage power supply side, and a circuit in which the capacitor 11 and the resistor 13 are connected in parallel to the diode 12 is connected between the emitter 3 and the extraction electrode 4. is inserted into. By the way, suppose that an extraction voltage is applied between the emitter 3 and the extraction electrode 4, an electron beam is generated, and the operating state is 3-, and the capacitor 11 is charged through the diode 12 to a voltage equal to the extraction voltage. . Further, the resistor 13 makes the diode 12 conductive in the forward direction, and compensates for the delay in diode operation due to accumulated carriers when an excessive voltage occurs and the charging current increases rapidly.At the same time, when the extraction voltage drops below a certain operating voltage, The terminal voltage of the capacitor 11 is lowered by this resistor 13 to follow it. Here, the ground capacitance of the accelerating voltage m7 is O3, the accelerating voltage is V, its internal resistance is R1, and the capacitance of the capacitor 11 is Co.

If the operating voltage (extraction voltage) of the emitter is Ve and its internal resistance is Ro, and if we consider the case where a vacuum discharge occurs between the extraction electrode 4 and the grounded anode 5, then FIG. It can be replaced as the equivalent circuit shown in the figure. In the figure, the switch (SW) is in the OFF state during normal operation, and when vacuum discharge occurs between the extraction electrode 4 and the anode 5, the SW can be considered to be in the ON state.

Here, the acceleration voltage V is 50KV, the emitter operating voltage 4-Ve is 3KV, and the capacitance of capacitor 11 (Co) is 0.
．． Since the ground capacitance C3 of the 1μF1 acceleration power supply V is generally about 100PF, in a vacuum discharge state (SW is ON), a voltage VS expressed by the following equation is applied between the emitter 3 and the extraction electrode 4. become.

Therefore, Vs =0. 5KV + 3KV=3. 5
Even if a vacuum discharge occurs between the extraction electrode 4 and the anode 5 due to KV, the voltage between the emitter 3 and the extraction electrode 4 will rise to about 3.5KV in the above example, but it will not reach the level of destroying the emitter. . Further, even when the accelerating voltage is high, the same effect can be obtained by appropriately selecting the capacitor capacitance CO based on the above relationship. In this way, it is possible to suppress excessive voltage from being applied between the emitter 3 and the extraction electrode 5 during vacuum discharge between the extraction electrode 4 and the anode 5, but if the capacitor 〇〇 is made large, the voltage between the emitter and the extraction electrode In the case of creeping discharge of an insulator (not shown) that insulates the extraction electrode from the structure of the emitter potential other than the emitter and mechanically holding the emitter, or vacuum discharge between the emitter potential structure and the extraction electrode, use a capacitor〇〇 Since the total accumulated charge contributes to the discharge, the vacuum surrounding the emitter worsens, and the tip of the field emitter is surrounded by positive ions, increasing the electric field strength at the emitter tip, causing the emitter to generate a vacuum discharge. It will be destroyed. For this reason, if the diode 12 is connected in series with the capacitor 11 as shown in Fig. 2, in the discharge between the emitter 3 and the extraction electrode 4, the charge accumulated in the capacitor 11 will be transferred to the diode 12. Therefore, the electrons cannot flow into the electron gun chamber, and when the vacuum dielectric breakdown between the extraction electrode 4 and the anode 5 occurs, which is the object of the present invention,
Excessive voltage application between the emitter 3 and the extraction electrode 4 can be suppressed, and furthermore, damage to the emitter due to vacuum discharge can be prevented without unnecessarily worsening the vacuum during vacuum discharge between the emitter 3 and the extraction electrode 4. be able to.

It should be noted that the present invention is not limited to the above-described embodiments; for example, the present invention can be applied to various ion sources that supply ionized substances to an emitter with a sharp tip and generate ions using a strong electric field. can be applied.

The present invention has been described in detail above, and according to the present invention, a parallel circuit consisting of a resistor connected in series with a diode and a tensor is added between the emitter electrode and the extractor electrode in parallel with the extractor power supply. Damage to the emitter can be prevented from occurring due to vacuum discharge between the electrode and the anode.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of a conventional field emission type electron gun, FIG. 2 is a configuration diagram showing an embodiment of the present invention, and FIG. 3 is an equivalent circuit diagram for explaining the present invention. . 1: Electron gun chamber, 2: Heating filament, 3: Emitter, 4: Extraction electrode, 5: Anode, 6: Insulated cable, 7:
Acceleration power supply, 8: Extraction power supply, 9: Filament heating power supply, 10: Power supply section, 11: Capacitor, 12: Diode, 13: Resistor. Figure 1

Claims (1)

[Claims] an emitter and an extraction electrode for forming a strong electric field necessary for field emission of charged particles near the tip of the emitter;
an acceleration electrode for accelerating charged particles emitted from the emitter; an extraction power source for supplying an extraction voltage between the emitter and the extraction electrode; and an acceleration power source for supplying the acceleration voltage between the emitter and the acceleration electrode. A field emission charged particle generator comprising a resistor connected in series with a diode and a parallel circuit of a capacitor added in parallel to the extraction power source.