WO2015092964A1

WO2015092964A1 - Electron beam emitter

Info

Publication number: WO2015092964A1
Application number: PCT/JP2014/005351
Authority: WO
Inventors: Kaveh Bakhtari
Original assignee: Hitachi Zosen Corporation
Priority date: 2013-12-19
Filing date: 2014-10-22
Publication date: 2015-06-25
Also published as: JP2016211850A

Abstract

An electron beam emitter (1) includes an electron generating source (2) generating electrons (e^-), a vacuum chamber (3) containing the electron generating source (2) in an interior (30), a transmission window (5) that keeps the airtightness of the vacuum chamber (3) and transmits the electrons (e^-), and a cooling mechanism (32), (31o), (31i) for cooling the transmission window (5). The transmission window (5) is formed of a pure material that is an anti-corrosive heat conductive material such as SiC and includes a thin membrane portion (50) transmitting the electrons (e^-) and a thick membrane portion (51) that has a continuous thickness. The thick membrane portion (51) includes an outer thick membrane portion on the circumference of the transmission window 5. The outer thick membrane portion is held by a wall (31) constituting the vacuum chamber (3) and is connected to the cooling mechanism (32), (31o), (31i).

Description

ELECTRON BEAM EMITTER

The present invention relates to an electron beam emitter.

An electron beam sterilizer for sterilizing containers such as beverage bottles with electron beams includes an electron beam emitter for emitting electron beams. Such an electron beam emitter includes an electron generating source capable of generating electrons and a vacuum chamber containing the electron generating source. The vacuum chamber is further provided with a transmission window that can transmit electrons. The transmission window includes membrane that transmits electrons and a grid that acts as a reinforcing member of the membrane and cools the membrane with heat transfer. It should be noted that the transmission window in a small size does not require the grid. In other words, the electron beam emitter accelerates electrons generated by the electron generating source in the vacuum chamber and passes the accelerated electrons through the transmission window so as to emit electron beams to the outside of the vacuum chamber. For such an electron beam emitter, disclosed is a transmission window having a configuration manufactured in a simplified manner (e.g., see Patent Literature 1).

In the electron beam emitter, not all of the electrons having reached the transmission window pass through the transmission window. Some of the electrons are absorbed by the transmission window, so that the transmission window rises in temperature. For this reason, a cooling mechanism for cooling the transmission window is generally provided on the electron beam emitter.

Further, the electron beam sterilizer, an ozone generator, and so on, in many cases, include the electron beam emitter disposed in the atmosphere. In these cases, since electrons emitted from the electron beam emitter generate highly corrosive factors (nitrogen oxide, ozone, nitric acid, and so on) as byproducts, the electron beam emitter is disposed in a highly corrosive environment.

Patent Literature 1: WO 1997/048114

However, the electron beam emitter described in Patent Literature 1 has the transmission window of multiple layers. These layers include at least a first layer 44 (or a second layer 46) and a corrosion stop layer 48 that are different in coefficient of thermal expansion, generating a thermal stress to easily cause damage on the bonded interface between the two layers. Meanwhile, if the corrosion stop layer 48 is not used in order to avoid a thermal stress, the transmission window may be corroded.

As described above, in the conventional electron beam emitter, the transmission window may be damaged or corroded, increasing the frequency of replacing the transmission window.

Accordingly, an objective of the present invention is to provide an electron beam emitter including a transmission window that is hardly damaged or corroded, reducing the frequency of replacing the transmission window.

In order to attain the objective, an electron beam emitter according to a first aspect of the present invention includes: an electron generating source capable of generating electrons; a vacuum vessel containing the electron generating source; a transmission window that keeps the airtightness of the vacuum vessel and is capable of transmitting the electrons from the electron generating source; and a cooling mechanism for cooling the transmission window, the transmission window being formed of a pure material that is an anti-corrosive heat conductive material and including a thin membrane portion that transmits the electrons and a thick membrane portion that is thicker than the thin membrane portion and has a continuous thickness, the thick membrane portion being positioned at least on the circumference of the transmission window, the thick membrane portion on the circumference of the transmission window being held by a wall constituting the vacuum vessel and connected to the cooling mechanism.

An electron beam emitter according to a second aspect of the present invention is the electron beam emitter according to the first aspect, wherein the anti-corrosive heat conductive material is at least one selected from the group consisting of Silicon Carbide, Silicon Nitride, Silicon, Sapphire, Aluminum Oxide, Silicon Dioxide, Diamond, and Aluminum Nitride.

An electron beam emitter according to a third aspect of the present invention is the electron beam emitter according to the first or second aspect, wherein the transmission window has a leveled surface on the external side of the vacuum vessel.

An electron beam emitter according to a fourth aspect of the present invention is the electron beam emitter according to the first or second aspect, wherein the thick membrane portion is connected to the cooling mechanism by brazing.

An electron beam emitter according to a fifth aspect of the present invention is the electron beam emitter according to the first or second aspect, wherein the thick membrane portion has a honey-comb structure.

An electron beam emitter according to a sixth aspect of the present invention is the electron beam emitter according to the first or second aspect, wherein the thick membrane portion is disposed radially from the center to the circumference of the transmission window.

An electron beam emitter according to a seventh aspect of the present invention is the electron beam emitter according to the first or second aspect, further including a moisture condensation preventing unit for keeping the temperature of the transmission window at a temperature for preventing moisture condensation, the moisture condensation preventing unit including a thermometer for measuring the temperature of the transmission window and a flow rate controller for controlling the flow rate of a coolant.

An electron beam emitter according to an eighth aspect of the present invention is the electron beam emitter according to the first or second aspect, wherein one of a reinforcing member and an anti-corrosive cover is disposed on the transmission window.

The electron beam emitter can reduce the frequency of replacing a transmission window since the transmission window is hardly damaged or corroded.

FIG. 1 is a schematic cross-sectional view showing an electron beam emitter according to a first embodiment of the present invention;

FIG. 2 shows the electron beam emitter wherein FIG. 2A is a perspective cross-sectional view of the electron beam emitter, and FIG. 2B is a cross-sectional view of the electron beam emitter taken along the line A-A of FIG. 2A (a plan view showing the transmission window of the electron beam emitter);

FIG. 3 is an isothermal diagram showing an enlarged cross section of the transmission window when a coolant is not circulated in the electron beam emitter;

FIG. 4 is an enlarged cross-sectional view showing the transfer of cooling by a coolant within a thick membrane portion, wherein FIG. 4A is an isothermal diagram of the thick membrane portion with a continuous thickness (present invention), and FIG. 4B is an isothermal diagram of the thick membrane portion with a discontinuous thickness;

FIG. 5 is a cross-sectional view showing a method for manufacturing the transmission window, wherein FIG. 5A shows a pure material of which the transmission window is formed, FIG. 5B shows that the pure material is laser-patterned, and FIG. 5C shows the manufactured transmission window;

FIG. 6 shows a transmission window in an electron beam emitter according to a second embodiment of the present invention and corresponds to FIG. 2B (the plan view of the transmission window);

FIG. 7 shows a transmission window in an electron beam emitter according to a third embodiment of the present invention and corresponds to FIG. 2B (the plan view of the transmission window);

FIG. 8 is an enlarged cross-sectional view showing a transmission window in an electron beam emitter according to a modification of the present invention; and

FIG. 9 is an enlarged cross-sectional view showing a transmission window in an electron beam emitter according to another modification of the present invention.

First Embodiment
An electron beam emitter according to a first embodiment of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, an electron beam emitter 1 includes an electron generating source 2 capable of generating electrons e^- and a vacuum chamber (vacuum vessel) 3 containing the electron generating source 2 in an interior 30. The vacuum chamber 3 is connected to a vacuum pump 4 (may be removable) that creates a vacuum in the interior 30. Further, the vacuum chamber 3 has a transmission window 5 that can transmit electrons e^- from the electron generating source 2. The transmission window 5 keeps airtightness in the vacuum chamber 3 along with a wall 31 constituting the vacuum chamber 3. In the vacuum chamber 3, the wall 31 on a part connected to the transmission window 5 has a double wall construction: an outer shell 31o and an inner shell 31i. A space between the outer shell 31o and the inner shell 31i circulates a coolant 32. The outer shell 31o and the inner shell 31i are connected to the transmission window 5 by brazing 35 (not limited to the brazing 35). It should be noted that the outer and inner shells 31o and 31i and the coolant 32 are an example of a cooling mechanism.
The transmission window 5 will be described below.

The transmission window 5 is made of an anti-corrosive heat conductive material, and as shown in FIG. 1, includes a thin membrane portion 50 that transmits electrons e^- and a thick membrane portion 51 that is thicker than the thin membrane portion 50. The thick membrane portion 51 acts as a reinforcing member for the transmission window 5. This enables the transmission window 5 to have a thinner part, which transmits electrons e^-, than a conventional transmission window with a uniform thickness. Thus, the transmission window 5 has a thinner part (that is, the thin membrane portion 50) that transmits electrons e-, hardly depriving the passing electrons e- of energy.

The anti-corrosive heat conductive material is at least one selected from the group consisting of Silicon Carbide, Nitrogen Carbide, Silicon, Sapphire, Aluminum Oxide, Silicon Dioxide, Diamond, and Aluminum Nitride. It should be noted that silicon carbide is most preferable for the anti-corrosive heat conductive material from a comprehensive perspective, that is, in terms of high anti-corrosion, high thermal conductivity, high strength, and so on.

As shown in FIG. 2, the thick membrane portion 51 includes an outer thick membrane portion 52 on the circumference of the transmission window 5 and an inner thick membrane portion 53 inside the outer thick membrane portion 52. The outer thick membrane portion 52 is cooled directly with the coolant 32 while the inner thick membrane portion 53 receives the transfer of cooling from the outer thick membrane portion 52, which will be detailed below. Further, the transmission window 5 has irregularities disposed so as to face the electron generating source 2, the irregularities being generated by a difference in thickness between the thin membrane portion 50 and the thick membrane portion 51. An opposite surface 55 of the irregularities (the outer side of the vacuum chamber 3) is leveled. It should be also noted that the transmission window 5 has the leveled opposite surface 55, hardly depriving passing electrons e^- of energy.

As specifically shown in FIG. 3, the outer thick membrane portion 52 is connected to the inner shell 31i by brazing 35i on the side of the electron generating source 2 and to the outer shell 31o by brazing 35o on the outer circumferential side. In other words, the outer thick membrane portion 52 is connected so as to be cooled directly with the coolant 32. However, since the thick membrane portion 51 is thicker than the thin membrane portion 50, the thick membrane portion 51 absorbs more electrons e^- than the thin membrane portion 50, so that the thick membrane portion 51 rises in temperature. Thus, as shown in FIG. 3, if the coolant 32 is not circulated, in the outer thick membrane portion 52, an area inside the inner shell 31i (H1 surrounded by a contour line) is heated to the highest temperature, followed by an area next to the area H1 (H2 surrounded by a contour line) followed by an area next to the area H2 (H3 surrounded by a contour line). Thus, the thick membrane portion 52 is connected so as to be cooled directly with the coolant 32, efficiently cooling the areas H1 to H3 having a high temperature.

As shown in FIG. 2, the inner thick membrane portion 53 is continuous with the outer thick membrane portion 52 in plan view. The inner thick membrane portion 53 is also continuous with itself. In other words, the inner thick membrane portion 53 is formed unicursally from the outer thick membrane portion 52. Thus, as is clear from the vertical section of FIG. 4A, the thick membrane portion 51 has a continuous thickness (uniform thickness as an example in FIG. 4A). The thick membrane portion 51 is cooled more efficiently than a thick membrane portion with a discontinuous thickness in FIG. 4B for the following reason:

FIGS. 4A and 4B each show that the thick membrane portion has a predetermined part (assumed to be a part in contact with the coolant 32) cooled and that the cooling is transferred within the thick membrane portion. In FIG. 4, in the thick membrane portion, an area C1 is directly cooled to the lowest temperature, followed by areas C2, C3, ..., and C9, in this order. The thick membrane portion 51 in FIG. 4A of the first embodiment has a continuous thickness. Thus, the cooling of the predetermined part is transferred without any interruptions to the areas C1, C2, ..., and C8, in this order. The area C8 has the highest temperature. In contrast, the thick membrane portion of FIG. 4B has a discontinuous thickness. Thus, the cooling of the predetermined part is transferred to the areas C1, C2, ..., and C9, in this order so as to circumvent the discontinuous portion. The area C9 has the highest temperature (a higher temperature than the area C8). Thus, the thick membrane portion 51 in FIG. 4A of the first embodiment is cooled more efficiently than the thick membrane portion in FIG. 4B, efficiently cooling the overall configuration. It should be noted that the transmission window 5 according to the first embodiment is made of an anti-corrosive heat conductive material, that is, a highly heat conductive material, further efficiently cooling the configuration.

As shown in FIG. 2, the inner thick membrane portion 53 has, for example, a honey-comb structure. Thus, the transmission window 5 is advantageous in strength, so that the outer thick membrane portion 52 and the inner thick membrane portion 53 can be reduced in thickness. This makes the transmission window 5 hard to absorb electrons e^- and have an extremely high temperature.

A method for manufacturing the transmission window 5 of the electron beam emitter 1 will be described below.

First, as shown in FIG. 5A, prepared is a pure material (that is, a single block or a single solid object) 5p that is made of the anti-corrosive heat conductive material with a uniform thickness.

Next, as shown in FIG. 5B, laser patterning is performed on the pure material 5p.

As shown in FIG. 5C, the laser-patterned portion is the thin membrane portion 50 and the remainder is the thick membrane portion 51, and the transmission window 5 is thus completed. The transmission window 5 is connected to the inner shell 31i and the outer shell 31o of the vacuum chamber 3 by the brazing 35.
The effects of the electron beam emitter 1 will be discussed below.

First, the vacuum pump 4 creates a vacuum in the interior 30 of the vacuum chamber 3. The coolant 32 is then circulated between the inner shell 31i and the outer shell 31o while the electron generating source 2 generates electrons e^-. The electrons e^- emitted from the electron generating source 2 are accelerated in the interior 30 to reach the transmission window 5. Most of the electrons e^- pass through the thin membrane portion 50 of the transmission window 5 and constitute electron beams for irradiation. On the other hand, the electrons e^- having reached the thick membrane portion 51 of the transmission window 5 are absorbed by the thick membrane portion 51, so that the thick membrane portion 51 rises in temperature. However, the high-temperature outer thick membrane portion 52 is cooled directly with the coolant 32. Further, since the high-temperature inner thick membrane portion 53 is continuous with the outer thick membrane portion 52 and the inner thick membrane portion 53 is continuous with itself, the cooling is efficiently transferred from the outer thick membrane portion 52. Moreover, the outer thick membrane portion 52 and the inner thick membrane portion 53 are each made of a highly heat conductive material (anti-corrosive heat conductive material), so that the inner thick membrane portion 53 is further efficiently cooled. For this reason, in the electron beam emitter 1, the transmission window 5 is further efficiently cooled with electron beams emitted from the transmission window 5.

As described above, since the transmission window 5 is further efficiently cooled without being heated to an extremely high temperature, the electron beam emitter 1 is hardly damaged by thermal expansion. Further, the transmission window 5 formed of the pure material 5p is hardly damaged even if thermal expansion occurs, unlike a transmission window including multiple material layers. The transmission window 5 made of a material with anti-corrosion (anti-corrosive heat conductive material) is hardly corroded. Since the transmission window 5 is hardly damaged or corroded, the electron beam emitter 1 can reduce the frequency of replacing the transmission window 5.

Since the transmission window 5 is hardly corroded, the electron beam emitter 1 can be prevented from being contaminated by particles generated by corrosion.

Second Embodiment
The electron beam emitter 1 of the first embodiment includes the inner thick membrane portion 53 having a honey-comb structure whereas an electron beam emitter 1 of a second embodiment includes an inner thick membrane portion 53 disposed radially from the center of a transmission window 5 toward an outer thick membrane portion 52 in plan view. The electron beam emitter 1 according to the second embodiment will be described below. In the following description, configurations different from those of the first embodiment will be explained, the same configurations as those of the first embodiment are indicated by the same reference numerals, and the explanation thereof is omitted.

As shown in FIG. 6, the inner thick membrane portion 53 according to the second embodiment includes, in plan view, radial main ribs 68 that are formed radially from around a center C of the transmission window 5 to the outer thick membrane portion 52 and parallel auxiliary ribs 69 that are in parallel with and shorter than the radial main ribs 68.

Thus, in the electron beam emitter 1 of the second embodiment, the radial main ribs 68 are extended linearly from the outer thick membrane portion 52 to around the center C of the transmission window 5, efficiently cooling even the center C of the transmission window 5 that is hardest to cool. In other words, in the electron beam emitter 1 of the second embodiment, the transmission window 5 is further efficiently cooled with electron beams emitted from the transmission window 5.

As described above, since the transmission window 5 in the electron beam emitter 1 of the second embodiment is more efficiently cooled than that of the first embodiment, the frequency of replacing the transmission window 5 can be reduced further.

Third Embodiment
The electron beam emitter 1 according to the first or second embodiment has the circular transmission window 5 in plan view whereas an electron beam emitter 1 according to a third embodiment has a rectangular transmission window 5 in plan view. The electron beam emitter 1 according to the third embodiment will be described below. In the following description, configurations different from those of the first and second embodiments will be explained, the same configurations as those of the first and second embodiments are indicated by the same reference numerals, and the explanation thereof is omitted.

As shown in FIG. 7, an inner thick membrane portion 53 according to the third embodiment includes, in plan view, a wide main rib 78 that is formed lengthwise so as to pass through a center C of the transmission window 5 and multiple narrow auxiliary ribs 79 that are formed widthwise from the wide main rib 78.

Thus, in the electron beam emitter 1 according to the third embodiment, the wide main rib 78 is extended linearly from an outer thick membrane portion 52 to the center C of the transmission window 5, efficiently cooling even the center C of the transmission window 5 that is hardest to cool. In other words, in the electron beam emitter 1 according to the third embodiment, the transmission window 5 is further efficiently cooled with electron beams emitted from the transmission window 5. Further, since the electron beam emitter 1 according to the third embodiment has the rectangular transmission window 5 in plan view, electron beams having a rectangular cross-section are emitted.

As described above, the electron beam emitter 1 of the third embodiment produces the same effect as the electron beam emitter of the second embodiment, and emits electron beams having a rectangular cross-section. Thus, the electron beam emitter 1 of the third embodiment is applicable for uses suitable for irradiation of electron beams having a rectangular cross-section (e.g., sterilization of the external surface of a container).

However, in the first to third embodiments, the outer thick membrane portion 52 and the inner thick membrane portion 53 are uniform in thickness but may be at least continuous with themselves.

In the first to third embodiments, the outer shell 31o, the inner shell 31i, and the coolant 32 were described as an example of a cooling mechanism but are not particularly limited. Any cooling mechanism may be used as long as the outer thick membrane portion 52 can be cooled.

In the first to third embodiments, the leveled surface 55 of the transmission window 5 was not specifically described but, as shown in FIG. 8, a cover 56 may be disposed on the surface 55. Examples of the cover 56 include covers that act as a reinforcing member (deposition membranes, Graphite, Carbon Nanotubes, atomic layer deposition), and anti-corrosive covers (Silicon Dioxide). Any of these examples has a thickness on the order of microns.

In the first to third embodiments, the pure material 5p is laser-patterned but other methods such as plasma etching may be employed.

Furthermore, the electron beam emitter 1 may include a moisture condensation preventing unit for preventing moisture from condensing on the transmission window 5. The moisture condensation preventing unit maintains the temperature of the transmission window 5 at a temperature for preventing moisture condensation. As shown in FIG. 9, the moisture condensation preventing unit includes a thermometer 7 for measuring the temperature of the transmission window 5 and a flow rate controller for controlling the flow rate of the coolant 32. The moisture condensation preventing unit prevents moisture from condensing on the transmission window 5, hardly corroding the transmission window 5. This can reduce the frequency of replacing the transmission window 5.

Claims

An electron beam emitter comprising:
an electron generating source capable of generating electrons;
a vacuum vessel containing the electron generating source;
a transmission window that keeps airtightness of the vacuum vessel and is capable of transmitting the electrons from the electron generating source; and
a cooling mechanism for cooling the transmission window,
the transmission window being formed of a pure material that is an anti-corrosive heat conductive material and including a thin membrane portion that transmits the electrons and a thick membrane portion that is thicker than the thin membrane portion and has a continuous thickness,
the thick membrane portion being positioned at least on a circumference of the transmission window,
the thick membrane portion on the circumference of the transmission window being held by a wall constituting the vacuum vessel and connected to the cooling mechanism.
The electron beam emitter according to claim 1, wherein
the anti-corrosive heat conductive material is at least one selected from the group consisting of Silicon Carbide, Silicon Nitride, Silicon, Sapphire, Aluminum Oxide, Silicon Dioxide, Diamond, and Aluminum Nitride.
The electron beam emitter according to claim 1 or 2, wherein the transmission window has a leveled surface on an external side of the vacuum vessel.
The electron beam emitter according to claim 1 or 2, wherein the thick membrane portion is connected to the cooling mechanism by brazing.
The electron beam emitter according to claim 1 or 2, wherein the thick membrane portion has a honey-comb structure.
The electron beam emitter according to claim 1 or 2, wherein the thick membrane portion is disposed radially from a center to the circumference of the transmission window.
The electron beam emitter according to claim 1 or 2, further comprising a moisture condensation preventing unit for preventing moisture from condensing on the transmission window,
the moisture condensation preventing unit including a thermometer for measuring a temperature of the transmission window and a flow rate controller for controlling a flow rate of a coolant.
The electron beam emitter according to claim 1 or 2, wherein one of a reinforcing member and an anti-corrosive cover is disposed on the transmission window.