ELECTRON BEAM IRRADIATION DEVICE AND METHOD FOR MANUFACTURING SAME

Abstract

An electron beam irradiation device includes a vacuum chamber having an electron beam generator inside, a vacuum nozzle, and a window foil on a tip of the vacuum nozzle. The electron beam irradiation device further includes an outer pipe surrounding the vacuum nozzle, a cooling-gas supply unit that supplies cooling gas into a coolant passage formed between the vacuum nozzle and the outer pipe, and a heat-conducting transmission foil fitted to the window foil and contacting the tip of the vacuum nozzle. The heat-conducting transmission foil has a value of at least 6310.sup.3, which is determined by dividing a thermal conductivity [W/(m.Math.K)] by a density [kg/m.sup.3], and a tip part of the vacuum nozzle is made of a material having at least a thermal conductivity of copper.

Claims

1. An electron beam irradiation device comprising: a vacuum chamber; an electron beam generator disposed in the vacuum chamber; a vacuum nozzle connected to the vacuum chamber with air tightness so as to guide an electron beam from the electron beam generator; a window foil that is disposed on a tip of the vacuum nozzle and allows the transmission of the electron beam from inside to outside of the vacuum nozzle; an outer pipe surrounding an outer surface of the vacuum nozzle; a cooling-gas supply unit that supplies cooling gas into a coolant passage formed as a clearance between the vacuum nozzle and the outer pipe; and a heat-conducting transmission foil that is fitted to the window foil and is in contact with the tip of the vacuum nozzle, wherein the heat-conducting transmission foil is made of a material having a value of at least 6310.sup.3, which is determined by dividing a thermal conductivity [W/(m.Math.K)] by a density [kg/m.sup.3], and at least a tip part of the vacuum nozzle is made of a material having at least a thermal conductivity of copper.

2. The electron beam irradiation device according to claim 1, wherein the heat-conducting transmission foil is made of beryllium, a carbon material, aluminum or silicon, or compounds thereof.

3. The electron beam irradiation device according to claim 1, wherein one of the window foil and the heat-conducting transmission foil with lower corrosion resistance is disposed near the vacuum nozzle.

4. The electron beam irradiation device according to claim 1, further comprising an adhesive member between the tip of the vacuum nozzle and one of the heat-conducting transmission foil and the window foil.

5. A method for manufacturing the electron beam irradiation device according to claim 1, comprising: forming the laminated foil by fitting the heat-conducting transmission foil to the window foil; placing the laminated foil on the tip of the vacuum nozzle; and connecting the vacuum nozzle to the vacuum chamber, wherein in the formation of the laminated foil, the window foil and the heat-conducting transmission foil are fitted to each other by pressure welding.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is schematic longitudinal section illustrating an electron beam irradiation device according to an embodiment of the present invention.

[0027] FIG. 2 is an enlarged view illustrating principal part of the electron beam irradiation device.

[0028] FIG. 3 is an exploded perspective view illustrating a longitudinal section of a laminated foil and an adhesive member in the electron beam irradiation device.

[0029] FIG. 4 is a schematic longitudinal section illustrating the electron beam irradiation device according to an example of the present invention.

[0030] FIG. 5 is an enlarged view illustrating a tip part of a vacuum nozzle as a principal part of the electron beam irradiation device.

DESCRIPTION OF EMBODIMENT

[0031] Referring to FIGS. 1 and 2, an electron beam irradiation device according to an embodiment of the present invention will be described below.

[0032] As illustrated in FIG. 1, an electron beam irradiation device 1 includes a vacuum chamber 2 in which an electron beam generator 21 is disposed, a vacuum nozzle 3 that is connected to the vacuum chamber 2 with airtightness so as to guide an electron beam B from the electron beam generator 21, and a window foil 4 that is disposed on the tip of the vacuum nozzle 3 and allows the transmission of the electron beam F from the inside of the vacuum nozzle 3 to the outside.

[0033] The vacuum chamber 2 is evacuated in order to accelerate the electron beam E from the electron beam generator 21. Power for generating the electron beam F is supplied to the electron beam generator 21 from, for example, a power supply disposed outside the vacuum chamber 2. The power supply is not illustrated. The vacuum nozzle 3 is evacuated along with the vacuum chamber 2. The window foil 4 seals the tip of the vacuum nozzle 3 and radiates the transmitted electron beam F to the outside of the vacuum nozzle 3. The transmission of the electron beam F heats the window foil 4. For cooling the window foil 4, the electron beam irradiation device 1 is configured as follows:

[0034] As illustrated in FIG. 2, the electron beam irradiation device 1 further includes an outer pipe 7 surrounding the outer surface of the vacuum nozzle 3, a cooling-gas supply unit 9 that supplies cooling gas C (e.g., air) into a coolant passage 8, that is, a clearance 8 between the vacuum nozzle 3 and the outer pipe 7, and a heat-conducting transmission foil 6 that is fit with a low density and a high thermal conductivity to the window foil 4 and is in contact with the tip of the vacuum nozzle 3. Additionally, at least a tip part of the vacuum nozzle 3 is made of a thermal conductive material (a material having at least a thermal conductivity of copper). In other words, in the electron beam irradiation device 1, heat from the window foil 4 is quickly transmitted to the tip part of the vacuum nozzle 3 by the heat-conducting transmission foil 6 and the transmitted heat is quickly transferred to the cooling gas C supplied into the clearance 8 between the vacuum nozzle 3 and the outer pipe 7. This configuration sufficiently cools the window foil 4 and thus eliminates the need for making the cooling gas C impinge on the window foil 4 directly through the outer pipe 7. Thus, the outer pipe 7 has a fixed internal diameter (including manufacturing errors such as a tolerance). The tip part of the vacuum nozzle 3 is made of the thermal conductive material (a material having at least a thermal conductivity of copper) and may have any length as long as heat from the window foil 4 is quickly transferred to the cooling gas C. For example, the tip part is at least four times longer than the internal diameter of the vacuum nozzle 3. If the tip part is at least four times longer than the internal diameter of the vacuum nozzle 3, an area exposed to the cooling gas C on the tip part is at least 16 times larger than the area of the window foil 4 (to be accurate, the area of one side inside the vacuum nozzle 3), that is, the tip part is so wide that heat transmitted from the window foil 4 to the tip part is quickly transferred to the cooling gas C.

[0035] The heat-conducting transmission foil 6 having a low density and a high thermal conductivity is foil made of a material having a value of at least 6310.sup.3, which is determined by dividing a thermal conductivity [W/(m.Math.K)] by a density [kg/m.sup.3]. The material satisfies Expression (1) below.

Thermal conductivity [W/(m.Math.K)]/density [kg/m.sup.3]6310.sup.3(1)

[0036] In addition to quick heat transfer with a high thermal conductivity from the window foil 4 to the tip part of the vacuum nozzle 3, the heat-conducting transmission foil 6 hardly generates heat even when the electron beam E is transmitted due to the low density. Examples of specific materials of the heat-conducting transmission foil 6, that is, examples of materials satisfying Expression (1) include beryllium, carbon materials (e.g., graphite, graphene, or a carbon nanotube), aluminum or silicon, or compounds thereof. Hereinafter, the window foil 4 and the heat-conducting transmission foil 6 fit onto the window foil 4 will be collectively referred to as a laminated foil 46.

[0037] The tip of the vacuum nozzle 3 and the heat-conducting transmission foil 6 may be hardly bonded to each other depending on the materials of the vacuum nozzle 3 and the heat-conducting transmission foil 6. In this case, as illustrated in FIG. 3, an exploded perspective view of a longitudinal section, an adhesive member 36 that is highly adhesive to both of the tip of the vacuum nozzle 3 and the heat-conducting transmission foil 6 may be interposed therebetween. In order not to hinder the passage of the electron beam E, the adhesive member 36 is ring-shaped. Also in the case where the adhesive member 36 is interposed, the heat-conducting transmission foil 6 and the tip of the vacuum nozzle 3 are preferably brought into contact with each other in order to quickly transmit heat from the heat-conducting transmission foil 6 to the tip part of the vacuum nozzle 3. In addition to the configuration of FIG. 3, the adhesive member 36 highly adhesive to both of the tip of the vacuum nozzle 3 and the window foil 4 may be interposed so as to indirectly bond the tip of the vacuum nozzle 3 and the window foil 4.

[0038] In view of quick transfer of heat from the heat-vacuum nozzle 3, it is preferably smooth the contact surfaces of the heat-conducting transmission foil 6 and the tip of the vacuum nozzle 3 (e.g., arithmetic mean roughness Ra0.4). Naturally, the smoothed contact surfaces achieve connection with firmer air tightness as well as quick transfer of heat.

[0039] A method for manufacturing the electron beam irradiation device 1 will be described below.

[0040] The method for manufacturing the electron beam irradiation device 1 includes a laminated foil forming step in which the heat-conducting transmission foil 6 is fitted to the window foil 4 so as to form the laminated foil 46, a laminated foil placing step in which the laminated foil 46 is placed on the tip of the vacuum nozzle 3, and a connecting step in which the vacuum nozzle 3 is connected to the vacuum chamber 2. In these steps, the laminated foil placing step follows the laminated foil forming step. The order of the connecting step is not limited.

[0041] In the laminated foil forming step, the window foil 4 and the heat-conducting transmission foil 6 are fitted to each other by pressure welding. In this case, pressure welding is a bonding method for applying heat and/or a pressure to the adjoining contact surfaces of the window foil 4 and the heat-conducting transmission foil 6 so as to metallically fuse the atoms of the window foil 4 and the heat-conducting transmission foil 6. The bonding method is, for example, diffusion bonding. The laminated foil 46 is formed by pressure welding, so that the window foil 4 and the heat-conducting transmission foil 6 are firmly fitted to each other. Thus, the laminated foil 46 is unlikely to be broken even under severe conditions such as a high pressure applied by sealing the evacuated vacuum nozzle 3 and heat generated by the transmitted electron beam F.

[0042] In the laminated foil placing step, in order to place the formed laminated foil 46 on the tip of the vacuum nozzle 3, the laminated foil 46 is bonded to the tip of the vacuum nozzle 3 by, for example, brazing.

[0043] In the connecting step, the vacuum chamber 2 and the vacuum nozzle 3 are directly connected to each other or indirectly connected to each other via a flange or the like (not illustrated). The vacuum chamber 2 in the connecting step may contain necessary devices such as the electron beam generator 21 and a power supply or the necessary devices may be disposed in the vacuum chamber 2 after the connecting step.

[0044] The operations of the electron beam irradiation device 1 will be described below.

[0045] First, power is supplied to the electron beam generator 21 from the power supply (not illustrated), so that the electron beam F is generated from the electron beam generator 21 as illustrated in FIGS. 1 and 2. The electron beam E is accelerated in the vacuum chamber 2 and the vacuum nozzle 3, is guided into the vacuum nozzle 3, and then passes through the laminated foil 46. This mainly heats the window foil 4. Heat from the window foil 4 is immediately transmitted to the tip part of the vacuum nozzle 3 through the heat-conducting transmission foil 6. The transmitted heat is quickly transferred to the cooling gas C supplied to the clearance 8 between the vacuum nozzle 3 and the outer pipe 7. Thus, the window foil 4 is sufficiently cooled.

[0046] In this way, the window foil 4 is sufficiently cooled in the electron beam irradiation device 1, thereby eliminating the need for a complicated configuration for cooling the window foil 4. This can achieve a simple configuration.

[0047] Moreover, the heat-conducting transmission foil 6 is made of the material that is easily obtained, such as beryllium, carbon materials, aluminum or silicon, compounds thereof, achieving a simpler configuration.

[0048] Furthermore, the adhesive member 36 placed as illustrated in FIG. 3 firmly bonds the heat-conducting transmission foil 6 to the tip of the vacuum nozzle 3, thereby improving the durability.

[0049] Additionally, according to the method for manufacturing the electron beam irradiation device 1, the window foil 4 and the heat-conducting transmission foil 6 are firmly bonded to each other by contact bonding, thereby further improving durability.

[0050] In the present embodiment, at least the tip part of the vacuum nozzle 3 is made of the thermal conductive material (a material having at least a thermal conductivity of copper). The thermal conductive material is used to transfer heat from the window foil 4 to the cooling gas C at least on the tip part of the vacuum nozzle 3. Thus, the part of the thermal conductive material (a material having at least a thermal conductivity of copper) in the vacuum nozzle 3 is preferably exposed as large an area as possible to the cooling gas C. In other words, the part of the thermal conductive material (a material having at least a thermal conductivity of copper) in the vacuum nozzle 3 preferably extends so as to be entirely surrounded by the outer pipe 7. As illustrated in FIGS. 1 and 2, the overall vacuum nozzle 3 is made of the conductive material (a material having at least a thermal conductivity of copper). This configuration is further preferable because heat is transferred from a part not surrounded by the outer pipe 7 in addition to the cooling gas C.

[0051] In the embodiment, the heat-conducting transmission foil 6 in the laminated foil 46 is illustrated near the vacuum nozzle 3. The window foil 4 may be disposed near the vacuum nozzle 3. In the laminated foil 46, the foil having lower corrosion resistance is disposed near the vacuum nozzle 3 and thus the laminated foil 46 becomes less corrosive, further improving the durability.

[0052] In the embodiment, the cooling-gas supply unit 9 supplies the cooling gas C. The cooling-gas supply unit 9 may supply and collect the cooling gas C (in other words, the cooling gas C is circulated). The cooling-gas supply unit 9 may be replaced with a cooling-liquid supply unit that supplies and circulates a cooling liquid (water or oil). This configuration is further preferable because the cooling liquid efficiently collects heat from the tip part.

[0053] Additionally, in the embodiment, the tip part of the vacuum nozzle 3 has a flat outer surface. The outer surface of the tip part may have a large number of grooves so as to increase the area of the tip part exposed to the cooling gas C. In particular, the grooves are more preferably formed perpendicularly to the axis of the vacuum nozzle 3 (that is, a large number of circumferential grooves) because the cooling gas C efficiently collects heat from the tip part. As a matter of course, the grooves may be replaced with a large number of projections. In order to more efficiently transfer heat from the tip part to the cooling gas C, a cooling fin may be provided on the tip part.

[0054] In the embodiment, the shape and thickness of the heat-conducting transmission foil 6 were not specifically described. The heat-conducting transmission foil 6 may have any shape and thickness as long as heat is quickly transferred from the window foil 4 to the tip part of the vacuum nozzle 3 and heat is hardly generated even when the electron beam E is transmitted due to the low density. For example, the heat-conducting transmission foil 6 is preferably so thick that heat other than heat transferred through the window foil 4 exposed to the atmosphere (other than convective heat transfer and thermal radiation) is completely transmitted to the tip part of the vacuum nozzle 3. Specifically, if the window foil 4 is a titanium foil having a thickness of 5 m and the heat-conducting transmission foil 6 is an aluminum foil having a thickness of 8 m, at least about 99% of heat generated on the titanium foil by the transmission of the electron beam E is transmitted to the tip part of the vacuum nozzle 3 so as to cool the titanium foil. This leaves only a small amount of heat on the titanium foil and thus the heat is sufficiently transferred through the titanium foil exposed to the atmosphere. Hence, a temperature increase on the titanium foil is suppressed. For comparison, in the related art where the heat-conducting transmission foil 6 is not provided (in other words, only the window foil 4 is provided) and the window foil 4 is a titanium foil having a thickness of 10 m, about 75% of heat generated on the titanium foil by the transmission of the electron beam E is transmitted to the tip part of the vacuum nozzle 3 so as to cool the titanium foil. This leaves a larger amount of heat on the titanium foil and thus the heat is not sufficiently transferred through the titanium foil exposed to the atmosphere. Hence, a temperature increase on the titanium foil is not suppressed.

[0055] A simulation was conducted to confirm the effect of the embodiment. First, conditions were set as follows: the titanium foil and the aluminum foil had the thicknesses described in the embodiment, the vacuum nozzle 3 had an internal diameter of 4 mm, and the electron beam E was generated so as to heat the tip and base of the vacuum nozzle 3 to temperatures of 700 K and 400 K, respectively. As a result, in the case of a foil including a titanium foil (5 m thick) and an aluminum foil (8 m thick) on the tip of the vacuum nozzle 3, the titanium foil was cooled by no less than 7.6 W without forced air-cooling. In contrast, in the case of a foil only including a titanium foil (10 m thick) on the tip of the vacuum nozzle 3, the titanium foil was cooled only by 1.2 W with forced air-cooling. Thus, it is assumed that the foil including the window foil 4 and the heat-conducting transmission foil 6, that is, the laminated foil 46 on the tip of the vacuum nozzle 3 is more resistant to the electron beam E having a large current.

EXAMPLE

[0056] According to a more specific example of the embodiment, the electron beam irradiation device 1 will be described below based on the accompanying drawings. Configurations omitted in the embodiment will be mainly discussed. The same configurations as those of the embodiment are indicated by the same reference numerals and the explanation thereof is omitted.

[0057] As illustrated in FIG. 4, the electron beam irradiation device 1 according to the example includes a vacuum pump 12 for evacuating the vacuum chamber 2 and the vacuum nozzle 3, and a vacuum L-shaped pipe 13 connecting the vacuum chamber 2 and the vacuum pump 12. Moreover, the electron beam irradiation device 1 includes an external flange 18 that fixes the vacuum nozzle 3 to the vacuum chamber 2 and guides the cooling gas C into the coolant passage 8, and a coolant pipe 19 connecting the external flange 18 and the cooling-gas supply unit 9.

[0058] The vacuum chamber 2 includes an internal flange 22 for fixing the electron beam generator 21. The internal flange 22 is disposed on the opposite end of the vacuum chamber 2 from the vacuum nozzle 3. The vacuum nozzle 3 is made of a copper alloy. The vacuum pump 12 is capable of setting the interiors of the vacuum chamber 2 and the vacuum nozzle 3 at a degree of vacuum (high vacuum to ultrahigh vacuum) suitable for accelerating the electron beam E. The vacuum L-shaped pipe 13 is positioned so as to separate the vacuum pump 12 from the electron beam E in the vacuum chamber 2 while locating the axis of the vacuum pump 12 in parallel with the axis of the vacuum chamber 2. Thus, even if a magnetic field is generated by the vacuum pump 12, the influence of the magnetic field on the electron beam E can be reduced.

[0059] The external flange 18 stably holds the vacuum nozzle 3 cantilevered from the vacuum chamber 2 and simplifies a structure from the coolant pipe 19 to the coolant passage 8, that is, a structure that guides the cooling gas C from the coolant pipe 19 to the coolant passage 8. The coolant pipe 19 is not particularly limited but is preferably short in length such that the cooling gas C does not collect heat other than heat from the vacuum nozzle 3, which is unnecessary heat.

[0060] As illustrated in FIG. 5, the window foil 4 is not limited as long as the window foil 4 allows the transmission of the electron beam E and is resistant to a high atmospheric pressure applied by sealing the evacuated vacuum nozzle 3. The window foil 4 is, for example, a titanium foil having a uniform thickness of about 1 m to 10 m (preferably about 3 m to 5 m). The heat-conducting transmission foil 6 is, for example, an aluminum foil similarly having a uniform thickness of about 2 m to 20 m (preferably about 5 m to 15 m). The laminated foil 46 including the window foil 4 and the heat-conducting, transmission foil 6 (strictly speaking, also including a boundary layer 5) is quite thin and always receives a high atmospheric pressure and thus is easily broken by an unexpected collision or the like. Thus, the structure is formed such that the laminated foil 46 disposed on the tip of the vacuum nozzle 3 is sufficiently surrounded by the outer pipe 7, that is, the tip of the outer pipe 7 projects out of the tip of the vacuum nozzle 3. The projection has any length as long as the laminated foil 46 is protected by the outer pipe 7. The projection is not shorter than, for example, the internal diameter of the vacuum nozzle 3.

[0061] A method for manufacturing the electron beam irradiation device 1 will be described below.

[0062] As the laminated foil forming step, the window foil 4 and the heat-conducting transmission foil 6 are fitted to each other by diffusion bonding. As illustrated in FIG. 5, through the diffusion bonding, the boundary layer 5 is formed between the window foil 4 and the heat-conducting transmission foil 6 by chemical bonding between the material of the window foil 4 and the material of the heat-conducting transmission foil 6. The boundary layer 5 has any thickness as long as the window foil 4 and the heat-conducting transmission foil 6 are fitted to each other. Thus, the time for diffusion bonding is set such that the boundary layer 5 is sufficiently thick.

[0063] The operations of the electron beam irradiation device 1 will be described below.

[0064] First, as illustrated in FIG. 4, the vacuum pump 12 evacuates the vacuum chamber 2 and the vacuum nozzle 3 to a degree of vacuum (high vacuum to ultrahigh vacuum) suitable for accelerating the electron beam E. Subsequently, power is supplied to the electron beam generator 21 from the power supply (not illustrated), so that the electron beam F is generated from the electron beam generator 21. The electron beam F is accelerated in the vacuum chamber 2 and the vacuum nozzle 3, is guided into the vacuum nozzle 3, and then passes through the laminated foil 46. This mainly heats the window foil 4. Heat from the window foil 4 is immediately transmitted to the tip part of the vacuum nozzle 3 through the heat-conducting transmission foil 6. Since the vacuum nozzle 3 is entirely made of a copper alloy, heat from the heat-conducting transmission foil 6 is transmitted over the vacuum nozzle 3. Most of the heat transmitted to the vacuum nozzle 3 is quickly transferred to the cooling gas C supplied into the clearance 8 between the vacuum nozzle and the outer pipe 7. Thus, the window foil 4 is sufficiently cooled.

[0065] In addition to the effect of the electron beam irradiation device 1 according to the embodiment, the electron beam irradiation device 1 of the present example achieves the following effect: The durability is further improved for the following reasons. Firstly, as illustrated in FIG. 5, the laminated foil 46 of the present example includes the boundary layer 5 firmly bonding the window foil 4 and the heat-conducting transmission foil 6 and is surrounded by the outer pipe 7. Secondly, as illustrated in FIG. 4, the vacuum nozzle 3 is fixed to the external flange 18 so as to be connected to the vacuum chamber 2.

[0066] In the example, the detail of the vacuum nozzle 3 was specifically determined and a simulation result was obtained as follows: The vacuum nozzle 3 was 150 mm in length, 4 mm in internal diameter, and 1 mm in thickness and was made of copper. The electron beam E was generated so as to heat the tip and base of the vacuum nozzle 3 to temperatures of 400 K and 300 K, respectively. In this case, a heat quantity of no less than 7.48 W was transferred and sufficient cooling was achieved. For comparison, under the same conditions except that the vacuum nozzle 3 was replaced with a stainless vacuum nozzle, only a heat quantity of 1.64 W was transferred and resulted in insufficient cooling.

[0067] The embodiment and the example are merely exemplary and are not restrictive in all the aspects. The scope of the present invention is not indicated by the foregoing description but the claims. The scope of the present invention is intended to include meanings equivalent to the claims and all changes in the scope. From among the configurations described in the embodiment and the example, the configurations other than that described as a first invention in Solution to Problem are optional and thus can be deleted and changed as appropriate.