JP2005214908A - Acceleration tube for electron beam accelerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent softening of adhesive used in an acceleration tube of electron beam irradiation device which is a laminate of glass rings and aluminum ring electrode in a multitude of pairs by bonding with an organic adhesive when a ring insulator and electrode are heated with a filament near the filament, fall of vacuum degree by exhaust of gas from the adhesive and shifting of the electrode and the insulator ring. <P>SOLUTION: The acceleration tube is a contact of tubes in the middle. A ceramic type acceleration tube formed by piling ring electrodes which is metallized ceramic ring by brazing, is in the filament side, and a glass made acceleration tube bonding with the organic adhesive by piling the glass insulator rings and ring electrodes by turns is in the ground side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a structure of an accelerator tube of an accelerator forming a part of an electron beam irradiation apparatus. An electron beam irradiation device heats a filament at a negative high voltage in a vacuum to generate thermal electrons, accelerates it with an accelerating tube, irradiates an object to be processed in the atmosphere with an electron beam through an irradiation window. It is an apparatus that performs processing such as crosslinking reaction, bactericidal action, and coating film curing. A transport mechanism for transporting an object to be processed in the atmosphere is provided so as to cross directly under the irradiation window.

  When an electron beam hits a solid, X-rays are generated, which oxidizes oxygen in the atmosphere and creates ozone. X-rays and ozone are harmful. Therefore, the irradiation window and the transport mechanism are housed in a casing made of a heavy metal plate or concrete. When handling a solid workpiece, the transport mechanism is often an endless conveyor. In the case of powder or granular material, a vibrating conveyor or the like is used. In the case of an object to be treated that does not have an ozone odor, an inert gas such as nitrogen or Ar is flowed into the casing to replace oxygen in the atmosphere.

  Therefore, the constituent elements of the electron beam irradiation apparatus are a high-voltage power supply, a vacuum evacuation apparatus, a filament, an acceleration tube, a scanning tube, an irradiation window, a housing, and a transfer device. The irradiation window is a window necessary for partitioning the vacuum and the atmospheric pressure. Ti and aluminum window foils are stretched around the window, which separates the vacuum from the atmosphere.

There are two types of electron beam irradiation devices depending on the acceleration voltage.
When accelerating to a high voltage of 3 MeV to 300 keV, the high-voltage power supply section is tall and the accelerating tube is long and the beam is narrow, so scanning is performed to the left and right. Since the beam is scanned, it is called a scanning type. For scanning, a scanning tube is provided following the acceleration tube. The scanning tube is a triangular tube with a wide bottom. There is a scanning coil in the upper part of the scanning tube, an alternating magnetic field is generated by the coil, and the beam is bent left and right and back and forth by Lorentz force. The accelerating tube is between the negative high voltage section and the ground voltage, and is formed by alternately stacking insulator rings and electrode rings. The electrode is provided with a voltage obtained by equally distributing the voltage between the ground voltage from the negative high voltage portion by a series resistor.

  In the case of low acceleration energy of 300 keV to several tens of keV, the acceleration tube is also small, and it is accelerated by a potential difference from the irradiation window (ground voltage) provided at the chamber outlet by simply providing a meandering filament with a negative voltage in the middle of the vacuum chamber It is. It is called non-scanning type or area type. The present invention relates to an improvement of an acceleration tube of a scanning electron beam irradiation apparatus having a long acceleration tube.

  The acceleration tube used in the electron beam accelerator has an insulating ring made of glass and an electrode made of a metal ring such as aluminum or titanium, which is stacked up and down. The electrode and the insulating ring are bonded with an adhesive. In addition to the effect of bonding the electrode and the glass, the adhesive also has the effect of maintaining a vacuum. In order to make the electric field applied to the beam straight in the axial direction, the electrodes are provided at equal distances so that the voltages between the electrodes are equal. For example, if the pitch per stage is 20 mm and the number of electrodes is 30, the total length of the acceleration tube is 600 mm. If the voltage between the electrodes is 20 kV, for example, a voltage of 600 kV can be applied to the electron beam in 30 stages.

  FIG. 1 is a longitudinal sectional view of an accelerating tube having a structure in which such a conventional glass ring and electrode alternate. The disk-shaped upper lid 5 is provided with electrode introduction terminals 3 and 3. The electrode introduction terminals 3 and 3 pass through the hole of the upper lid and hold the filament 4 at the lower end thereof. Thermoelectrons are emitted from the filament. The upper lid 5 is fixed to the upper flange of the trunk portion 6 with screws. The body 6 is a metal cylinder, and an accelerating tube is continuously provided from the lower flange. The extraction electrode 7 extracts the thermoelectrons from the filament toward the acceleration tube.

  The acceleration tube is formed by stacking an appropriate number of stages of ring-shaped glass insulating rings 8 and electrodes 9 and forms a cylindrical space for accelerating the electron beam. The electrode 9 and the glass insulating ring are bonded with an organic adhesive. A voltage dividing resistor is provided outside, and a voltage obtained by equally distributing the acceleration voltage between the electrodes is applied. The electrode interval (pitch) is 20 mm. For example, a 30-stage acceleration tube has a length of 600 mm. One stage can be multiplied by 20 kV to 30 kV. With such a structure, an acceleration tube having an acceleration voltage of 500 keV to 800 keV can be formed. If it exceeds 500 keV, it becomes a relativistic region, and the speed of electrons becomes very close to the speed of light.

  Such an accelerating tube is a general one and has a structure adopted in an accelerating tube of many electron beam irradiation apparatuses. Such a glass ring accelerating tube has advantages that it is easy to manufacture, has low material costs, and is low in cost. Since the glass ring is transparent, there is also a convenient point that the inside of the accelerating tube can be observed from the outside. As long as it is at room temperature, the action of the adhesive is sufficient, the mechanical adhesive strength is sufficient, and the function of maintaining a vacuum is also achieved.

Although a publicly known technique should be shown, there is no appropriate literature regarding an electron beam irradiation apparatus acceleration tube. Glass / adhesive accelerator tubes were so common that no attempt was made to improve them. Patent Document 1 discloses a novel device for aging in an acceleration tube. This does not say what the structure of the accelerating tube is. It can be seen from the drawing that the accelerating tube has an insulating portion and an electrode portion that overlap each other, and the voltage dividing resistor gives an appropriate partial pressure to the electrode. There was almost no invention of the accelerating tube itself, and a conventional example could not be found.
Japanese Patent Laid-Open No. 7-311300 “Electron Beam Irradiation Device”

  The adhesive that bonds the glass ring and the metal plate functions as an adhesive up to about 100 ° C., but starts to soften at a temperature of 100 ° C. or lower.

  The electrode and insulating ring close to the filament are heated by receiving heat radiation from the filament. When heat radiation is insufficient, the electrode plate and glass ring in the vicinity of the filament may be heated to 70 ° C to 80 ° C. Then, the adhesive begins to soften. At the same time, gas is generated from the adhesive. Gas deteriorates the degree of vacuum in the accelerating tube. It causes collisions between electron beams and gas molecules, resulting in electron beam loss.

  Even if the adhesive softens, leakage does not occur and the vacuum can still be maintained, but the adhesive itself becomes fluid. It is still good if the ring-shaped electrodes and glass are stacked in the vertical direction, but there are cases where the accelerator tube is installed in the horizontal direction and the electrodes and glass rings are arranged side by side. In such a case, when the adhesive becomes fluid, the glass ring and the electrode ring are shifted downward due to weight. When this happens, the electron beam path is not straight but curved, and the electron beam collides with the electrode. When a collision occurs with the electrode, a desired current value cannot be obtained, so that the processing capacity is reduced. It also increases power loss. There is also a possibility that the electrode is heated excessively and the temperature of the adhesive rises to cause a vacuum leak from the acceleration tube.

  As an alternative to glass + adhesive accelerated tubes, ceramic discs and metallized accelerated tubes have been proposed. A ceramic disk is used as an insulator, and both sides thereof are metallized and brazed with an electrode plate. However, it is difficult to metallize and braze, and the manufacturing cost is high.

The present invention employs a ceramic type acceleration tube composed of a plurality of stages in which ceramic insulators are metallized on a plurality of stages on the electron source (filament side) and brazed electrodes, and a glass insulator and electrodes are disposed on the ground side (irradiation window side). A multi-stage glass-type acceleration tube bonded with an adhesive is used, and the acceleration tube is joined at the middle portion to form a single acceleration tube.
As a means for joining, the upper and lower accelerating pipes are separately manufactured and joined with an adhesive, or mechanically joined through a metal seal. Either may be sufficient. When bonding with an adhesive is employed, there is no deviation in the electrode pitch.

  However, the mechanical coupling using a metal plate causes a slight deviation in the pitch between the electrodes. Describe that. Since a sufficiently stable beam size can be obtained by accelerating from the electron source to about 200 keV, the number of accelerating tube stages (about 5 stages) corresponding to this 200 keV is manufactured by the ceramic method, and the downstream glass bonding method. Joining with an accelerating tube and bolts is the optimum method.

The electron source of the electron beam irradiation apparatus is equipped with a thermionic electron gun that heats the filament. For this reason, an accelerator tube with a small amount of released gas and a high heat-resistant temperature and excellent heat-resistant temperature characteristics is particularly required on the electron gun side of the accelerator tube. On the other hand, the ground side acceleration tube is not heated gently and is not heated. On the other hand, it is required to install an acceleration tube that is greatly deteriorated by X-rays incident from the ground side and can be easily replaced at low cost.
The effect described in the subject can be obtained by skillfully combining the accelerating tubes made by two kinds of production methods.

The acceleration tube of the electron beam irradiation apparatus according to the embodiment of the present invention will be described with reference to FIG.
It is written to have almost the same structure as that of the glass insulator type in FIG. However, the material of the insulators in the upper and lower parts is actually different, and the upper and lower parts are joined using metal flanges. There is a difference.

  The disk-shaped upper lid 5 is provided with electrode introduction terminals 3 and 3. Ceramic insulator rings 23 are fitted into holes formed in two places of the upper lid 5 so that the electrode introduction terminal 3 and the upper lid 5 are insulated. The electrode introduction terminals 3 and 3 extend through the hole 26 of the upper lid 5 and hold the filament 4 at the lower end thereof. The filament 4 is heated by flowing a current from the current introduction terminal, and thermoelectrons are emitted from the filament 4.

  The upper lid 5 is fixed to the upper flange 32 of the trunk portion 6 with screws 27. The trunk | drum 6 is a metal cylinder. The body 6 and the upper lid 5 are hermetically held by interposing a metal packing, and are coupled by a screw 27. An accelerating tube is subsequently provided from the lower flange 33 of the body 6. A bottomless cup-shaped extraction electrode 29 is attached inside the first stage electrode of the acceleration tube. Thermal electrons emitted from the filament 4 are extracted toward the acceleration tube by the Wehnelt electrode 7 and the extraction electrode 29. The acceleration tube is a combination of two upper and lower structures.

The five stages on the filament side are obtained by alternately stacking ring-shaped ceramic insulating rings 38 and electrode rings 39 made of Ni, Ti or the like. Although this figure is omitted, in practice, there are many cases where 20 stages or 30 stages are connected. The ceramic insulating ring is, for example, alumina (Al ₂ O ₃ ). The insulating ring 38 has a groove and a step on the inner peripheral surface, and the outer peripheral portion is flat. The inner and outer surfaces of the ceramic insulating ring 38 remain ceramic, but the upper and lower end surfaces are metallized. By performing this treatment, Mo and Ti of the ceramic plate and the electrode can be brazed. Aluminum electrodes cannot be used because they cannot be brazed.

  The important thing is not to use glass and polymer adhesive. Since it is metallized on a ceramic insulator and attached to a metal electrode by brazing, it will not be violent at about 100 ° C. It does not soften or peel like a polymer adhesive. Brazing is robust even when heated by the radiant heat of the filament, and the amount of gas released by heating is small. That is, it becomes excellent in heat resistance. On the other hand, since the ceramic is opaque, the inside cannot be crazed. For convenience, the upper half is temporarily called a ceramic-type acceleration tube.

  The lower half is a conventional glass insulating ring 8 and aluminum electrode 9 bonded together with a polymer adhesive and stacked alternately. Here, six steps are shown, but there are actually many more. Let's call the lower half a glass-type acceleration tube. Since the lower half is far from the filament, it is difficult to be heated by the filament heat. Therefore, the adhesive is not heated by radiant heat, and gas is not emitted or softened from the adhesive. The electrode and glass do not skid. Moreover, it is convenient that only the lower half is transparent and the inside can be seen with the naked eye. Furthermore, the one closer to the illumination window needs to be replaced more frequently, but it is advantageous that it is a cheaper glass mold.

  It does not have to be exactly half up and down. Since the radiation is already weak at the 5th to 6th stage from the filament, the ceramic mold is only the upper 6th stage, and the lower part may be a glass mold. Since the ceramic mold is expensive, it may be used only near the filament.

  The electrode spacing is the same for the upper ceramic accelerator tube and the lower glass accelerator tube. For example, the pitch can be 20 mm. In the case of a 60-stage accelerating tube, half may be distributed to a ceramic mold and a glass mold, such as 30 stages and 30 stages. Further, only the upper six steps may be ceramic, and the lower 54 steps may be glass.

  The upper ceramic-type acceleration tube and the lower glass-type acceleration tube can be joined with an adhesive. However, it takes time and effort to remove the adhesive when only the lower half is replaced.

  Another means is to use a metal flange. Here, a metal flange is used to couple with a screw. The upper ceramic-type acceleration tube is terminated by an upper flange 40 that also serves as an electrode. The lowermost ceramic insulating ring 38 is brazed to the upper flange 40. The upper flange has a plurality of screw holes. The lower glass-type acceleration tube has a ring-shaped lower flange 42 on the upper end surface. There are several female threads 44 in the lower flange. The upper and lower flanges 40 and 42 are overlapped at an intermediate portion, and are coupled by screwing the bolt 43 through the female screw hole 44 from the through hole.

  There is a circumferential step on the mating surface of the upper and lower flanges 40, 42, and a metal seal is sandwiched between them and crushed. If the upper and lower accelerating tubes are coupled using such a metal flange, it is easy to replace only the lower half. X-rays are generated because of electron beams, but X-rays are generated near the irradiation window, which can contaminate the lower half of the accelerator tube more. Therefore, when the glass accelerator tube is adopted in the lower half, it becomes more convenient because only the lower glass accelerator tube needs to be replaced.

  However, if the two are joined with a metal flange, the pitch between the electrodes is slightly shifted at the joint. For this reason, the electric field distribution may be non-uniform. For example, assume that a voltage of 20 kV is applied between the electrodes, and the number of electrodes in 30 stages is an acceleration voltage of 600 kV in total. In this case, the electrode interval can be 20 mm in the upper half ceramic acceleration tube, and the electrode interval can be 20 mm in the lower half glass acceleration tube. However, at the joint where two metal flanges are sandwiched, the electrode spacing is 20 mm or more, for example, 30 mm. Since the voltage between the electrodes is still 20 kV, the electric field there is slightly weakened.

  However, if the electron beam is accelerated to 200 keV or more, the beam is sufficiently accelerated and fast so that there is no fear that the beam will spread even if the electric field is somewhat weakened. Therefore, a metal joint can be provided in a portion after 200 kV. It is also possible to use ceramic from the filament side up to about 200 kV and then glass. Therefore, if the interstage voltage is, for example, 30 kV, the seventh stage from the top can be ceramic, and the lower stage can be glass.

The schematic sectional drawing of the acceleration pipe | tube concerning the prior art example which laminated | stacked what laminated | stacked the glass insulator ring and the ring electrode alternately, and joined with the organic adhesive agent. A ceramic-type accelerator tube made of metallized ceramic rings and laminated with a ring electrode is laminated on the filament side, and glass laminate rings and ring electrodes are alternately stacked on top of each other with an organic adhesive. The schematic sectional drawing of the acceleration pipe | tube concerning this invention joined by the intermediate part by making the joined glass type acceleration pipe | tube into the ground side.

Explanation of symbols

3 current introduction terminal 4 filament 5 upper lid 6 barrel 7 Wehnelt electrode 8 ring-shaped glass insulator 9 lead aluminum electrode 23 insulator ring 26 hole 27 screw 29 lead electrode 32 upper flange 33 lower flange 34 ring 35 screw 38 ceramic insulating ring 39 nickel Electrode ring 40 Upper flange 42 Lower flange 43 Bolt 44 Female screw hole

Claims (1)

A ceramic-type acceleration tube made of metallized ceramic rings and brazed with ring electrodes is laminated on the filament side, and multiple layers of alternately laminated glass insulator rings and ring electrodes are stacked on the filament side. An acceleration tube for an electron beam accelerator, characterized in that a glass-type acceleration tube bonded with an organic adhesive is bonded to the ground side and bonded at an intermediate portion.

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