JPH11101896A - Electron beam irradiation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To open and close an electron beam faster than the opening and closing of a mechanical shutter by providing a power source and a switch between an acceleration tube electrode and a filament, and switching voltage between positive or negative. SOLUTION: Two sets of power sources and switches are provided between a filament F and a first electrode E1, the switch SW1 and the negative power source V1 are connected in series, and the switch SW2 and the positive power source V2 are connected in series. At normal operation, since SW1 is closed, SW2 is opened, and the filament becomes more negative potential than the electrode E1, a thermal electron is attracted to the electrode, and an electron beam comes out into an acceleration tube to be accelerated. Reversely, when SW1 is opened and SW2 is closed, the electron is returned to the filament since filament potential is higher than the electrode E1, and an electron ray beam instantly stops. The beam can be blocked only by the opening and closing of the switch, and since a large shutter plate need not be moved, it is performed in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam irradiation apparatus capable of turning on and off an electron beam instantaneously. The electron beam irradiator generates electrons from an electron gun in a vacuum, accelerates them into a beam, takes it out to the atmosphere through a window foil, and irradiates an object to be processed. There are a scanning type that scans a beam and a non-scanning type that does not scan a beam. In the case of scanning type, electron beam generator, accelerating tube, scanning mechanism,
It consists of a scanning tube, an irradiation window, a window foil, a transport mechanism, a housing and the like. The electron beam generator generates electrons by heating the cathode filament to generate thermoelectrons. The accelerating tube accelerates electrons by applying a voltage with multi-stage electrodes. The scanning unit generates a magnetic field by the coil, and thereby bends the electron beam. The beam can be scanned left and right by applying an alternating magnetic field. The scanning tube is a triangular tube with an expanded lower side.

[0002] At the lower end of the scanning tube is an irradiation window. Here is a window foil. The window foil cuts off the upper vacuum section and the lower atmospheric pressure section. There is a transport mechanism, whereby the object to be processed is carried from the entrance to the exit immediately below the irradiation window. The transport mechanism is surrounded by a shielding plate such as a lead plate or an iron plate or a housing made of concrete. When an electron beam hits the object to be processed, X-rays are generated. In order to prevent this from leaking to the outside, it is necessary to skillfully shield the electron beam irradiation section immediately below the irradiation window. In addition, ozone is generated when the electron beam reacts with oxygen. This is also harmful. So, flowing nitrogen gas etc. to the irradiation part to prevent ozone generation,
Some measures are taken, such as treating ozone after generation to an allowable concentration or less. The present invention relates to an improvement in a device for opening and closing a beam in such an electron beam irradiation device.

[0003]

2. Description of the Related Art A schematic configuration of a conventional scanning electron beam irradiation apparatus 1 will be described with reference to FIG. A high voltage is guided upward by the cable 2. The cathode filament is heated by the electron beam generator 3 to generate thermoelectrons, and the anode (irradiation window)
Electrons are extracted as a beam by the electric field between. The accelerating tube 4 following this accelerates to a desired energy by passing an electron beam between a plurality of perforated electrodes obtained by dividing a high voltage. The electron beam is accelerated downward.

[0004] The z-axis is taken in the direction of the electron beam. Scan direction is y
Direction. The direction of transport of the workpiece is the x direction. The acceleration energy varies. For example, when accelerating to 300 keV or more, a scanning type of multi-stage acceleration is used. The scanning mechanism 5 is made up of a coil, and swings the electron beam 7 left and right by changing the magnetic field alternately at, for example, sinωt. The scanning tube 6 is a trapezoidal vacuum container having a widened downward portion, and an electron beam 7.
Gives space to swing left and right. At the lower end of the scanning tube 6, there is an irradiation window 8 on which a window foil is stretched.

An object 9 passes in the x-direction just below the irradiation window 8. At that time, the electron beam passing through the window foil hits the object, cross-linking the polymer, curing the coating, and sterilizing. It acts like. The window foil is a foil of Ti, Al, or the like.

[0006] A transport mechanism such as a transport conveyor is provided immediately below the irradiation window 8, and a workpiece 9 placed on the transport mechanism passes therethrough. In the case of a continuous object to be processed, such as a tape, the tape is unwound without being put on a conveyor, and is put between rollers and the rollers are turned.

[0007] A mechanical shutter 10 is provided to temporarily interrupt the electron beam irradiation. This is a metal plate that can enter and exit between the irradiation window and the workpiece. It reciprocates linearly in the xy plane or rotates around the y axis. When the shutter 10 comes below the irradiation window 8, the electron beam 7 hits the shutter 10 and is blocked. Shutter 1
Numeral 0 is for temporarily blocking the electron beam by mechanical means. Even if the electron beam remains emitted, closing the shutter can cut the electron beam and prevent the electron beam from hitting the workpiece. The electron beam irradiation can be restarted by opening the shutter.

[0008]

The irradiation window is a wide window having a long side of 1 m or more. Sometimes it exceeds 2m. Because it is a shutter that covers the whole of this, it is quite large. Since it is necessary to withstand repeated irradiation of the electron beam, it must be made of metal. Since it is quite heavy, it has a large inertia. No matter how fast you move, there is a limit. There is also the inertia of motors and reducers. It takes a few seconds to close a heavy shutter. If you want to shut off the electron beam quickly, that is not enough. Conversely, there is also a delay of one to two seconds to open the shutter when electron beam irradiation begins.

Depending on the intended use, it may be desired to turn on and off more quickly. For example, there is a new demand for instantaneously raising and lowering a beam for an object running at a high speed. In mechanical opening and closing, the time delay is inevitably large and does not meet the purpose. It is an object of the present invention to provide a device capable of opening and closing an electron beam (electron beam) more quickly than opening and closing of a mechanical shutter.

[0010]

A new power supply and two switches in opposite directions are provided between the electrode of the accelerating tube and the filament to switch the voltage V between the accelerating tube electrode and the filament in the positive and negative directions. Generate and stop the electron beam. Let C be the voltage of the accelerating tube electrode and F be the filament voltage. If F> C, the electron beam does not proceed in the electrode direction because the filament has a high potential. The time required for opening and closing is shortened because the electron beam is blocked by an electric means instead of a mechanical means.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a conventional electron beam irradiation apparatus, voltage distribution between a filament and an electrode of an accelerating tube has been performed by arranging voltage dividing resistors in series. Therefore, the accelerating tube electrode was always higher in potential than the filament voltage. A conventional power supply structure will be described with reference to FIG. The filament F is a thin wire such as W and is heated by a DC power supply Vf (or an AC power supply) to generate thermoelectrons. The filament is biased to a negative voltage by the negative high voltage power supply Vab.

The electrodes E1, E2, E3,... Are metal plates having an opening at the center and are arranged in a straight line immediately below the filament. An insulator exists between the electrodes, and the accelerating tube is used as a vacuum chamber by the insulator. However, the illustration of the insulator is omitted here. A negative voltage Vac is applied to the filament, and the voltage is divided by the resistance strings R1, R2, R3 and the like and applied to the accelerating electrodes E1, E2,... Thus, a voltage dropped by the drop due to the voltage dividing resistor is applied to the acceleration electrode. When the filament voltage F and the electrode potential are represented by E1, E2,..., F <E1 <E2
<E3 ... This relationship is fixed.
It cannot be changed.

According to the present invention, a positive / negative power source and a switch are provided between any one of the electrodes of the accelerator tube En and the filament,
The potential between the electrode and the filament can be changed to positive or negative. Although any electrode may be used, the uppermost first electrode E1 is optimal. Since the voltage difference between the first electrode and the filament is the smallest, the power supply and the switch need only have a small capacity, and the wiring is the simplest. The switch used in the present invention is not limited to a mechanical switch, and includes an electric switch using a semiconductor or the like and having no movable part.

FIG. 3 shows a first embodiment of the present invention.
An embodiment will be described. Filament F and first electrode E1
There are two sets of power supplies / switches between them. one is,
The switch SW1 and the negative power supply V1 are connected in series. The other is that the switch SW2 and the positive power supply V2 are connected in series. Switches SW1 and SW2 are interlocked and open and close complementarily. When one is open, the other is closed. Opening and closing are performed simultaneously.

When SW1 is closed and SW2 is open,
Since the filament has a more negative potential than the electrode E1, thermoelectrons are attracted by the electrode. The electron beam exits the acceleration tube and is accelerated. The electron beam hits the object, and the object undergoes electron beam processing. This is the state during normal operation.

When SW1 is open and SW2 is closed, the filament potential becomes higher than that of the electrode E1. F> E1
(= C). For this reason, the electrons are driven back to the filament by the electrode E1. The electron beam stops instantaneously. The beam can be cut off simply by opening and closing the switch. Since it is not necessary to move a large shutter plate, it can be completed in a short time. When SW1 is closed and SW2 is opened, a beam is generated.

In this example, the negative power supply Vac is connected to the filament F. Then, the voltage of the accelerating tube electrode becomes S
It varies with W1 and SW2. If this is not desirable, a negative power supply Vac may be connected to the first electrode E1.

[Embodiment] In the above-described example, two power supplies are used to switch the relative potential of the filament to the electrode between positive and negative. Using this as a single power supply can reduce costs. FIG. 4 shows such an embodiment. A power supply V3 and two switches SW3 and SW4 that open and close complementarily are provided between the filament F and the first electrode E1. SW
The contact b of No. 3 and the contact a of SW4 are connected to the positive pole of the power supply V3. The contact a of SW3 and the contact b of SW4 are connected to the negative pole of V3.

SW3 and SW4 simultaneously contact the a contact or the b contact. When the filament is in contact with the a-contact, thermoelectrons are extracted because the filament has a negative voltage with respect to the electrode. An object is irradiated with an electron beam. SW
3. When the SW4 is switched to the contact b, the filament has a positive potential (F> E1 = C) with respect to the electrode.
Electrons are rejected by the electrode E1. The electron beam does not pass through the acceleration tube. The electron beam stops. This also allows the beam to be opened and closed instantly by electrical means.

[Embodiment] Of the accelerating tube electrodes, it is convenient to switch the potential between the first electrode and the filament to positive or negative, but the present invention is not limited to this. Generally, a power supply V1 (positive) is provided between the n-th electrode En (= C) and the filament,
V2 (negative) may be provided to switch the potential between F and En between positive and negative. When F> C, the electron beam stops. When F <C, the electron beam flows between the electrodes. In that case, an acceleration power supply Vac is connected to the first electrode E1.

[0021]

Conventionally, a large shutter is moved between the irradiation window and the object to be processed, so that it takes time to open and close the beam. In the present invention, the beam is generated and stopped by switching the bias voltage between the accelerating tube electrode and the filament to positive or negative. The time required for on / off is reduced. The beam rises and falls quickly, and it is also possible to control the irradiation of an electron beam to a high-speed traveling object with precision. It is possible to prevent a defective portion such as an unprocessed portion or a portion where the dose is exceeded from being generated on the workpiece.

[Brief description of the drawings]

FIG. 1 is a front view schematically showing an electron generation unit, an acceleration tube unit, a scanning tube, and the like of a scanning electron beam irradiation apparatus.

FIG. 2 is a circuit diagram showing a potential relationship between a filament and an accelerating tube electrode according to a conventional example.

FIG. 3 In the first embodiment of the present invention, two power sources and two switches are provided between the filament and the accelerator tube electrode.
FIG. 9 is a circuit diagram showing that the filament is set at a high potential (F> E) with respect to the electrode to stop the beam, and the filament potential is set at a low potential with respect to the electrode so as to extract the beam.

FIG. 4 shows a second embodiment of the present invention, in which one power supply and two switches are provided between the filament and the accelerating tube electrode;
High potential of filament F with respect to electrode E (F> E)
FIG. 6 is a circuit diagram showing that the beam is stopped by setting the filament potential to a low potential with respect to the electrode to extract the beam.

[Explanation of symbols]

 F Filament E1 First electrode of accelerating tube E2 Second electrode of accelerating tube E3 Third electrode of accelerating tube V1 Power source for applying a negative potential to filament to V1 electrode V2 Power source for applying a positive potential to filament to electrode Vf Filament power source Vac acceleration Power supply R1 First voltage divider R2 Second voltage divider R3 Third voltage divider

Claims (1)

[Claims] 1. One or two DC power supplies and two switches are provided between a filament and one electrode of an acceleration tube, and an electron beam is switched between the filament and the acceleration tube by switching the potential of the filament with respect to the electrode between positive and negative. An electron beam irradiating apparatus characterized in that the electron beam irradiating device is passed or stopped.