AU708665B2

AU708665B2 - Hydronic cooling of particle accelerator window

Info

Publication number: AU708665B2
Application number: AU16281/97A
Authority: AU
Inventors: Joseph R. Lovin; David S. Shevick
Original assignee: Cryovac LLC
Current assignee: Cryovac LLC
Priority date: 1992-10-01
Filing date: 1997-03-17
Publication date: 1999-08-12
Anticipated expiration: 2013-10-01
Also published as: AU1628197A

Description

P:\OPERCAE\1628197.106 -16/6/99 -2- There is thus a significant need for improvement with regard to the cooling of electron beam accelerator windows.

SUMMARY OF THE INVENTION According to the present invention there is provided a method of irradiating an article, comprising the steps of: providing an electron beam accelerator, said accelerator comprising a window, a target region, and a heat pipe for cooling the window; said heat pipe comprising a hollow tube having an evaporator section in contact with the window and a condenser section, a volatile liquid in said hollow tube, and a wick; irradiating an article in the target region; cooling the window while irradiating the article; and providing an inert gas to the target region during the irradiating to substantially decrease 000.0: 15 ozone production.

o to According to a preferred embodiment of the present invention there is provided an t "electron beam accelerator, said accelerator comprising a particle accelerator window, a target region, and a plurality of heat pipes, each of said heat pipes comprising a hollow tube having an evaporator section in contact with the window and a condenser section, a volatile liquid in said hollow tube, and a wick; irradiating an article in the target region and thereby causing the particle accelerator window *to heat, thereby heating the liquid and converting the liquid to a vapor to thereby cool the particle accelerator window;

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condensing the vapor to reform the liquid; 25 returning the reformed liquid to the evaporator section of the particle accelerator through the wick; and providing an inert gas to the target region during the irradiating to substantially decrease ozone production.

According to a further aspect of the present invention there is provided an article when irradiated by a method as defined in either of the preceding paragraphs.

In a preferred aspect, the inert gas is nitrogen.

Advantageously, the present invention reduces or eliminates the air available for /Sz z R ionization during the cooling of such windows.

P:\OPER\CAE\16281-97.106- 16/6/99 2A- These as well as other advantages are preferably achieved by an improvement to an electron beam accelerator, used in the method of the present invention, in the form of heat pipes located on the window structures of such a generator for the cooling of such window by such heat pipes. The heat pipes eliminate the need for air cooling and thus reduce or eliminate the production of ozone.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of a method in accordance with the invention will now be described by way of example only, with reference to the accompanying drawings in which: Figure 1 of the drawings illustrates schematically the operation of a heat pipe.

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Figure 2 of the drawings illustrates schematically an electron beam accelerator in

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association with an x-ray target or product to be irradiated.

Figure 3 of the drawings is an isometric view of an electron beam accelerator window assembly in accordance with this invention.

20 DETAILED DESCRIPTION I In accordance with this invention, it has been found that the window of an electron beam accelerator may be cooled by the placement thereon of heat pipes for the conduction of heat away therefrom. It is most surprising in accordance with this invention that heat pipes o 25 function without deterioration in the environment of an electron beam accelerator. Various other advantages and features will become apparent from a reading of the following description given with reference to the various figures of drawing.

P:\OPER\CAE\16281-97.106 16/6199 -3- Heat pipes have been utilized in a variety of applications since their inception. They have been most utilized in the art of injection molding but also utilized in the nuclear reactor art. As used herein and shown schematically in figure 1, a heat pipe is generally a hollow tube having a volatile substance therein. The heat pipe is normally formed of thermally conductive material and upon placement of the tube within a heat environment, the volatile liquid within the heat pipe vaporizes and absorbs the heat energy from the portion of the heat pipe subjected to the heat load. This causes the liquid at that point to boil and enter a vapor state. When that happens, the liquid picks up the latent heat of vaporization in passing from the liquid to vapor state. The gas which then has a higher pressure moves toward the center of the sealed container and away from the heat source to a cooler location where it is condensed by external means of cooling. When the gas is condensed, it gives up the latent heat of vaporization. The liquid medium is then returned toward the heat source through the heat pipe wick.

The heat pipe thus functions to transfer heat from the input to output end of the heat

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15 pipe with effective thermal conductivities many thousands of times that of copper heat sinks.

For example, a heat pipe is described in U.S. Patent No. 4,601,331 which utilizes a heat pipe in the environment of a microwave tube collector. Such patent is hereby incorporated by :e reference.

Figure 2 of the drawings illustrates an electron beam accelerator and/or x-ray 20 generator of the type applicable to the current invention. Referring to figure 2 of the drawings, there is illustrated an electron beam accelerator 1 and an x-ray generator 3. The electron beam accelerator generally has a filament 5 from which electrons are emitted and passed through a high voltage divider network 7 through a plurality of anodes 9 to arrive in a scan coil assembly 11. In passing through the scan coil assembly, the electrons are scanned 25 through a scanning horn 13 to contact a window 15 such as that described above. An electron 17 is illustrated as having passed through the window and headed toward a metal x-ray target 21 or product to be irradiated. In a preferred aspect of the present invention, an article to be irradiated may be a polymeric material, coating or ink.

After traversing through the window the high speed electrons interact with the stream of air being used to cool the window resulting in ionization of the air molecules and consequently the formation of ozone and NO, products.

Referring to figure 3 of the drawings, a window assembly 31 is illustrated having a P:\OPER\CAE\16281-97.106 16/6/99 window mounting bracket 33, foil window 35 and a plurality of heat pipes illustrated here as 37, 39 and 41. Heat pipes 37, 39 and 41 rest upon window 35 for the conducting of heat away therefrom. There is illustrated also as a part of the window assembly 31, external cooling means 45 which are preferably water cooling for the heat pipes 37, 39 and 41.

A preferred heat pipe for utilization with this invention is a heat pipe from Noren Company of Menlow Park, California, which utilizes either mercury or water as the volatile liquid. Surprisingly, both have been found to operate in the environment of the electron accelerator.

One of the advantages associated with the use of heat pipes for cooling an electron window is that the entire electron beam x-ray generator or product irradiation chamber may be isolated in nitrogen and generally the entire environment is isolated except for the cooling water. Therefore, there are no adverse effects to the environment associated with ozone production. The generally inert surrounding of nitrogen also provides for the likelihood of oooea longer life of all equipment in that environment.

15 It is thus seen that this invention provides a significant improvement in the cooling of electron beam accelerator windows. It further seen that this improvement eliminates the production of ozone which has heretofore been associated with electron beam accelerators.

o* As many variations become apparent to those of skill in the art from a reading of the 2 foregoing description, such variations are embodied within the spirit and scope of this .i 20 invention as defined by the following appended claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be :understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

P:\OPER\CAE\16281-97.106- 16/6/99 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A method of irradiating an article, comprising the steps of: providing an electron beam accelerator, said accelerator comprising a window, a target region, and a heat pipe for cooling the window, said heat pipe comprising a hollow tube having an evaporator section in contact with the window and a condenser section, a volatile liquid in said hollow tube, and a wick; irradiating an article in the target region; cooling the window while irradiating the article; and providing an inert gas to the target region during irradiation to substantially decrease ozone production.

2. A method of irradiating an article, comprising the steps of providing an electron beam accelerator, said accelerator comprising a particle accelerator window, a target region, and a plurality of heat pipes, each of said heat pipes comprising a hollow tube having an evaporator section in contact with the window and a condenser section, a volatile liquid in said hollow tube, and a wick; airradiating an article in the target region and thereby causing the particle accelerator window to heat, thereby heating the liquid and converting the liquid to a vapor to "-athereby cool the particle accelerator window; :.:condensing the vapor to reform the liquid; returning the reformed liquid to the evaporator section of the particle accelerator through the wick; and providing an inert gas to the target region during the irradiating to substantially decrease ozone production.

3. The method of claim 1 or 2, wherein the inert gas is nitrogen.

4. The method of any one of claims 1-3, wherein the article comprises a polymeric material.

The method of any one of claims 1-3, wherein the article comprises a coating.

Claims

6. The method of any one of claims 1-3, wherein the article comprises an ink.
7. An article when irradiated by a method in accordance with any one of claims 1-6. DATED this 16th day of June, 1999. Cryovac, Inc. By DAVIES COLLISON CAVE Patent Attorneys for the applicant 4 S 5 5* 5* a* a. S *5 S S S S. S S S. 5555 S. S S S S S S S S a
55555. S P:\OPER\CAE\16281-97.106 16/6/99 -7- ABSTRACT OF THE DISCLOSURE A method of irradiating an article using an electron beam apparatus window having improved cooling associated therewith, which is in the form of heat pipes located on the window of such apparatus for the cooling of such window by such heat pipes, whereby the heat pipes eliminate the need for air cooling and thus eliminate the production of ozone. .9 *e 9*q*