JPS5913143B2 - charged particle device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charged particle beam device, and more particularly to a device configured to suppress surge voltage generated within a power supply device thereof.

An example of an electron beam device, which is a type of charged particle device, will be explained.

FIG. 1 is a conceptual diagram showing a conventional electron beam device. 1 is a power supply device, which includes a bias power supply 10, a cathode heating power supply 11, an electron beam acceleration power supply 12 including a smoothing reactor 13 and a capacitor 14, and voltage dividing resistors 15, 16. It consists of a discharge gap 17.

2 is a coaxial cable with core wires 21, 22, 23. It is composed of an external shield 24, 3 is an electron gun, is composed of a cathode 31, a Wehnelt electrode 32, and an anode 33, 34 is an electron beam,
35 indicates spark discharge in vacuum.

The terminal of the cathode 31 is connected to the cathode heating power source 10 via the core wires 22 and 23 of the coaxial cable, and is also connected to the negative electrode of the electron beam accelerating power source 12 via dividing resistors 15 and 16.

The Wehnelt electrode 32 is connected to the bias power supply 1 via the core wire 21.
0 negative electrode.

The grounded anode 33 connects to the outer shield 24 of the coaxial cable.
It is connected to the positive electrode of the electron beam accelerating power source 12 via.

In the conventional electron beam device configured in this way,
The inside of the electron gun 3 is evacuated by an exhaust device, which is omitted in FIG. Thermionic electrons emitted from the cathode 31 are accelerated by the voltage applied between the cathode 31 and the anode 33, and an electron beam 34 is generated.

Since a high voltage for accelerating the electron beam 34 is applied between the cathode part consisting of the cathode 31 and the Wehnelt electrode 32 and the anode 33, the Wehnelt electrode located on the outermost periphery of the cathode part and facing the anode is applied. A spark discharge 35 may occur in vacuum between the electrode 32 and the anode 33.

In particular, in the electron gun 3 used for electron beam welding, electron beam melting, etc., spark discharge 35 in a vacuum is likely to occur because some of the generated metal vapor flows into the electron gun 3 .

When the Wehnelt electrode 32 and the anode 33 are short-circuited due to spark discharge 35 in vacuum, the accelerating power source 12 charged to a high voltage
Charge is supplied from the smoothing capacitor 14 of the bias power supply 10, and a surge voltage is generated at the output terminal of the bias power supply 10.

In order to absorb this surge voltage, in the conventional device, a discharge gap 17 is connected between the output terminals of the bias power supply 10 as shown in FIG.

However, since the rise of the surge voltage is steep compared to the response speed of the discharge gap 17, the surge voltage cannot be suppressed sufficiently, and when the repeated vacuum spark discharge 35 occurs, the insulation between the bias power supply 10 and the core wire gradually deteriorates. The drawback was that it deteriorated over time, eventually leading to dielectric breakdown.

This invention was made with the aim of eliminating the above-mentioned drawbacks of the conventional device, and it slows down the rise speed of the surge voltage generated inside the power supply device due to vacuum spark discharge that occurs inside the electron gun, so that the surge voltage can be used as an arrester. The overshoot voltage during the period from when the operating voltage is reached until the arrester operates is suppressed to suppress the peak value of the surge voltage.

FIG. 2 is a conceptual diagram showing one embodiment of this invention.
is exactly the same as the conventional device mentioned above.

An arrester 40 for absorbing surge voltage, a capacitor 41 connected between the output terminals of the bias power supply 10 and a parallel body of a resistor 42 for discharging the charge charged in the capacitor 41 are connected to the output terminal of the electron beam acceleration power supply 12. The current limiting resistor 43 and the current limiting reactor 44 are connected in series.

FIG. 3 shows an equivalent circuit when a vacuum spark discharge 35 occurs between the Wehnelt electrode 32 and the anode 33 in the electron beam apparatus constructed as described above.

In the figure, R8 is a current limiting resistor 43, Le is a current limiting reactor 44, Z is an arrester 40, C8 is a capacitor 41,
R8 is a resistor 42, S is a switch indicating the presence or absence of spark discharge 35 in vacuum, Eo is an electron beam acceleration power supply voltage, and E is a surge voltage applied between the output terminals of the bias power supply 10.

The surge voltage E until the arrester 40 operates is expressed by the following equation.

When the time for the surge voltage to reach the operating voltage E2 of the arrester 40 is T, and the response time of the arrester 40 is t, the wavefront value Emax of the surge voltage can be approximated by the following equation.

If the response time t of the arrester 40 is taken into account and the value of (dE/dt)T obtained from equation (1) is designed to be small, the wavefront value Emax of the surge voltage can be suppressed within a predetermined voltage.

As an example, a design example in which the wavefront value of the surge voltage E is set to 1ooov or less is shown below, and the rising waveform of the surge voltage E in the design example is shown in FIG.

However, to simplify the explanation, the output voltage of the bias power supply 10 is assumed to be zero.

(Design example) In Fig. 4, the rising speed of surge voltage E (dE/
dt) is regulated to approximately 100V/μS, the overshoot voltage during a 1μs response time of the arrester 40 is 100VC−.

Wavefront value Emax &! of surge voltage E Since the value is the sum of the arrester suppression voltage of 900v and the overshoot voltage of 100v, the surge voltage E is suppressed to the set voltage of 1ooov or less.

In this embodiment, in order to slow down the rise speed of the surge voltage E, a current limiting resistor is installed at the output end of the electron beam accelerating power source 12.
Although the current limiting resistor 43 and the current limiting reactor 44 are connected in series, the same effect can be expected even if the current limiting resistor 43 or the current limiting reactor 44 is connected alone.

Further, although a resistor 42 is connected to discharge the charge accumulated in the capacitor 41 due to the surge voltage, the internal impedance of the bias power supply 10 may be used instead.

By the way, in the above embodiment, an electron beam device using an electron beam generator with a triode structure was described as an example, but it is also possible to use an electron beam device or ion beam device that generates charged particles using an electron beam generator of other structure. It will be obvious without much explanation that it is broadly applicable to devices that perform

As is clear from the above description, this invention includes a parallel arrangement of an arrester and a capacitor connected between the output terminals of a control power source for charged particle generation, and a current limiting element inserted in series at the output end of the charged particle acceleration power source. When a spark discharge occurs in a vacuum in a charged particle generator, the rising speed of the surge voltage induced between the output terminals of the control power supply for charged particle generation is delayed, and this surge voltage is It is possible to suppress the wavefront value within a predetermined value, and as a result, it is possible to eliminate dielectric breakdown that occurs between the control power supply device for charged particle generation and the core wire of the coaxial cable.

In addition, since the wavefront value of the surge voltage can be suppressed to a low value, the withstand voltage of the charged particle generation power supply and the withstand voltage between the cores of the coaxial cable can be made low, so that the device can be made inexpensive. can.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of a conventional electron beam device, Fig. 2 is a conceptual diagram showing an embodiment of the present invention, and Fig. 3 is a spark discharge in vacuum inside the electron gun in the electron beam device shown in Fig. 2. FIG. 4 is a diagram showing an example of the rising waveform of the surge voltage in the equivalent circuit diagram shown in FIG. 3. In the figure, 1 is a power supply, 2 is a coaxial cable 3 is an electron gun, 10 is a bias power supply, 11 is a cathode heating power supply, 12 is an electron beam acceleration power supply, 13 is a smoothing reactor of the electron beam acceleration power supply 12, and 14 is an electron Smoothing capacitor of beam acceleration power source 12, 15.16 voltage dividing resistor, 17 surge voltage absorption discharge cap, 21, 22, 2
3 is a core wire of the coaxial cable 2, 24 is an outer shield of the coaxial cable, 31 is a cathode, 32 is a Wehnelt electrode, 33 is an anode, 34 is an electron beam, 35 is a spark discharge in vacuum, 40
41 is a surge voltage absorbing arrester, 42 is a resistor for discharging the capacitor 41, 43 is a current limiting resistor, and 44 is a current limiting reactor. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A charged particle generator, a power supply device comprising a charged particle generation control power source and a charged particle acceleration power source that supply predetermined driving power to each electrode of this generator, and this power source device and the above-mentioned charged particle generator. In a charged particle device composed of a coaxial cable connecting a particle generator, a parallel body of a capacitive element and a voltage-dependent conductive element connected between output terminals of the control power source and an output terminal of the acceleration power source. and a current limiting element inserted in series on the acceleration power source side. 2. The charged particle device according to claim 1, wherein the current-limiting element is a resistor or an axle, or a series body of a resistor and an axle. 3. The charged particle device according to claim 1, wherein the voltage-dependent conductive element is an arrester such as a discharge gap or a voltage-dependent resistor.