Abstract:
A system and method to provide uniform, high intensity radially inwardly directed electron beams to the interior of a cylindrical volume for the purpose of destroying toxic, hazardous, or noxious organic and/or inorganic compounds contained in air or other media flowing through a cylindrical region; or to destroy or inactivate bacteria, viruses, fungi, or mold spores in such flowing media; to sterilize contents of flowing media; to treat fluidized grains, herbs, or other products; or to destroy chemical warfare agents. A window assembly to transmit electromagnetic radiation, for example, an electron beam, x-rays, or other high energy electromagnetic radiation, is also disclosed.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application relates to U.S. Provisional Patent Application No. 61/135,138 filed on Jul. 17, 2008, entitled RADIALLY INWARDLY DIRECTED ELECTRON BEAM SOURCE FOR TREATMENT OF FLOWING MEDIA, which is hereby incorporated herein in its entirety by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to apparatus and processes for producing electromagnetic energy, and, more particularly, to systems and methods to transmit high energy electromagnetic radiation from a source to an external region, for example, to treat materials and, more particularly, to treat a flow of matter containing a harmful or noxious component. Specifically, one embodiment of the present invention provides a system and method to provide a uniform, high-intensity electron beam to the interior of a cylindrical volume for the purpose of destroying toxic, hazardous, or noxious organic and/or inorganic compounds contained in air or other media flowing through a cylindrical region, so as to destroy or inactivate bacteria, viruses, fungi, or mold spores in such flowing media; or to sterilize the contents of flowing media; or to treat fluidized grains, herbs, or other similar products to provide sterilization; or to destroy chemical warfare agents. Another embodiment of the present invention provides a system and method to provide a high-intensity electron beam or other electromagnetic radiation, for example, x-ray radiation, to the interior of a cylindrical utilization region or other external region. 
     2. Description of the Prior Art 
     Various devices are known for producing electromagnetic radiation. Known devices and processes include electron beam devices and other devices such as devices that produce x-rays. A beam of electrons or x-rays is controlled to radiate energy for any of a variety of purposes well-known to persons skilled in the art. 
     For example, various devices are known for destroying toxic, hazardous, or noxious organic and/or inorganic compounds contained in flowing air or other media. Known devices and processes include electron beam devices. A beam of electrons irradiates the flowing air or other media to destroy the toxic, hazardous, or noxious organic and/or inorganic compounds contained in the flowing media. 
     The configurations of known electron beam and other electromagnetic radiation devices may typically incorporate a structure to control the emitted radiation, but are not generally conducive to the effective and efficient transmission of the emitted radiation or the dissipation of heat that is generated. Moreover, known configurations are not scalable. 
     For example, the configurations of known electron beam devices are not generally conducive to the effective and efficient treatment of the flowing media. Moreover, known configurations are not scalable to treat large volumes of flowing media. 
     It would be desirable to provide a solution that overcomes the disadvantages of known electron beam and other electromagnetic radiation devices. More particularly, it would be desirable to provide an electron beam or other electromagnetic radiation system and method that effectively and efficiently transmit the emitted radiation and dissipate heat. It would also be desirable to provide such a system and method that are scaleable. It would also be desirable to provide a solution that overcomes the disadvantages of known electron beam devices for treating flowing media. More particularly, it would be desirable to provide an electron beam system and method that effectively and efficiently treat the flowing media. Additionally, it would also be desirable to provide such a system and method that are scaleable to treat various volumes, including large volumes, of flowing media. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, a system and method are provided for transmitting an electron beam, x-rays, or other form of high energy electromagnetic radiation from an evacuated space in which the radiation is generated to an external region, for example, to treat flowing media. In accordance with one embodiment, the system comprises an electron beam generator that preferably employs a thermionic cathode. Advantageously, cold electron emission cathodes do not require heating power. In accordance with one preferred embodiment, the electron beam generator comprises a cold electron emitting surface in sheet form, which can be shaped to different patterns of emission, and emits electrons from a large surface area. The cathode is disposed on the inside of a cylinder. Constructed with or without a control grid, and with an applied negative high voltage between the cathode and a grounded cylinder of smaller diameter, for example, a tube or window assembly, a beam of electrons is accelerated in a direction perpendicular to the common axis of the cylinders. The smaller cylinder is preferably provided with windows constructed of sufficiently thin material, so that the electrons pass through such windows into an inner cylindrical region within the smaller cylinder. The electrons irradiate flowing media passing through the inner cylindrical region. In accordance with a preferred embodiment, the flowing media passing through the inner cylindrical region is effectively and efficiently processed for the purpose of destroying toxic, hazardous, or noxious organic and/or inorganic compounds contained in air or other gaseous media flowing through the cylindrical region, so as to destroy or inactivate bacteria, viruses, fungi, or mold spores in such flowing media; or to sterilize the contents of the flowing media; or to treat fluidized grains, herbs, or other similar products to provide sterilization; or to destroy chemical warfare agents. 
     In accordance with another aspect of the present invention, a window component subassembly is provided comprising an outer cylinder that provides a means of mechanical support and heat conduction for an inner cylinder. The cylinders have a plurality of slits that comprise windows through which an electron beam, x-rays, or other form of high energy electromagnetic radiation is transmitted. 
     The outer cylinder may be comprised of a single material with the required mechanical strength, thermal conductance, and thermal expansion coefficient as required for the construction of the window subassembly, or a plurality of cylinders and segments that together provide the required characteristics if use of a single cylinder of material with the required characteristics is prohibited by practical and/or economic factors. The inner cylinder is preferably bonded to the outer cylinder to enable the transfer of heat to keep the window areas of the inner cylinder cool during operation. The material for the inner cylinder has properties such that the radiation passes through it with a minimum of absorption and reflection. The material must also have sufficient mechanical strength to withstand the differential pressure between the vacuum and application space and be available as a thin foil because the absorption and reflection of the radiation increases with the thickness and density of the material. 
     The thermal expansion coefficients of the inner and outer cylinders are approximately equal to minimize the mechanical stress and distortion of the cylinders during the bonding process construction of the window component subassembly. 
     An additional cylinder having an outside diameter smaller than the inside diameter of the inner foil window cylinder and bonded to it may be added to the window component subassembly to further reduce mechanical and thermal stress in the window foil and/or to reduce or prevent corrosion of the inner surface of the window foil by material being treated in the application space. In accordance with one embodiment, both the inner window foil cylinder and the additional cylinder are constructed from titanium. 
     In accordance with one example, the supporting or outer cylinder is comprised of a copper cylinder to provide the high thermal conductance and a 410S stainless steel cylinder that has an expansion coefficient nearly equal to the thermal expansion coefficient of the titanium foil window material. 
     In accordance with a preferred embodiment, a window component subassembly is provided wherein the additional cylinder preferably comprises an inner sleeve having a given outside diameter and preferably constructed from a titanium alloy. The inner sleeve has a plurality of slits which comprise windows for radiation. The window component subassembly further comprises an outer cylinder comprising an outer sleeve having a given inside diameter that is greater than the outside diameter of the inner sleeve and a given outside diameter. The outer sleeve is preferably constructed from a metal having a relatively high coefficient of thermal expansion, for example, OFE grade copper. 
     The window component subassembly also preferably comprises an outer support having a given inside diameter that is larger than the outside diameter of the outer sleeve. Preferably, the subassembly comprising the outer sleeve and outer support is then brazed together using a braze sheet, for example, a copper-gold-nickel material, disposed between the outer sleeve and the outer support. The brazed subassembly is then provided with a plurality of slits which comprise windows for radiation. 
     Preferably, a foil comprising the inner cylinder, for example, a titanium alloy foil, is placed around the circumference of the additional cylinder comprising the inner sleeve so as to overlie the slits in the inner sleeve. The foil-wrapped inner sleeve is slid into the outer sleeve so that the slits of the inner sleeve align with the slits of the outer sleeve and outer support. 
     Additionally, in accordance with a preferred embodiment, a window assembly incorporating the window component subassembly is provided. The window subassembly additionally comprises a first end support subassembly and a second end support subassembly preferably each constructed from a metal having a relatively high coefficient of thermal expansion, for example, OFE grade copper. The first and second end support subassemblies each comprise a flange having an outside diameter that is less than the inside diameter of the inner sleeve of the window component subassembly. The flanges are slid into the opposite ends of the inner sleeve. A tubular mandrill having a higher coefficient of thermal expansion is then inserted through the interior of the first and second end support assemblies and the inner sleeve. The window assembly is then heated to form a diffusion bond between the first and second end support subassemblies and window component subassembly. 
     The foregoing and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of various embodiments, which proceeds with reference to the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The various embodiments of the present invention will be described in conjunction with the accompanying figures of the drawing to facilitate an understanding of the present invention. In the figures, like reference numerals refer to like elements. In the drawing: 
         FIG. 1  is a schematic cross-sectional view illustrating one embodiment of the system in accordance with an aspect of the present invention. 
         FIG. 2  is a cross-sectional view along line A-A of  FIG. 1 . 
         FIG. 3 , comprising  FIGS. 3A and 3B , is an isometric view of a preferred embodiment of the system in accordance with the present invention. 
         FIG. 4  is a detailed isometric cross-sectional view of the system shown in  FIG. 3 . 
         FIG. 5  is a detailed isometric view of one preferred cathode and control grid structure. 
         FIG. 6  is a detailed isometric view of an alternative cathode and control grid structure. 
         FIG. 7  illustrates an electron beam pattern produced in the system in accordance with the present invention. 
         FIG. 8  is a flow diagram illustrating a method in accordance with one embodiment of the present invention. 
         FIG. 9  is an isometric view illustrating a preferred embodiment of the window assembly in accordance with another aspect of the present invention. 
         FIG. 10  shows an end support subassembly comprising the window assembly of  FIG. 9 . 
         FIG. 11  is an isometric view of an end support comprising the end support subassembly of  FIG. 10 . 
         FIG. 12  is an isometric view of an end sleeve comprising the end support subassembly of  FIG. 10 . 
         FIG. 13  is an isometric cross-sectional view illustrating manufacture of the end support subassembly of  FIG. 10 . 
         FIG. 14  shows brazing induced strain produced as a result of manufacture of the end support subassembly of  FIG. 10 . 
         FIG. 15  shows an isometric view partially in cross-section of a window component subassembly comprising the window assembly of  FIG. 9  positioned within a tool used for manufacture of the window component subassembly. 
         FIG. 16  is an isometric cross-sectional view of an outer cylinder comprising an outer sleeve comprising the window component subassembly shown in  FIG. 15 . 
         FIG. 17  is an isometric view of an inner cylinder comprising foil preferably placed around the circumference of a portion of an additional cylinder comprising an inner sleeve comprising the window component subassembly shown in  FIG. 15 . 
         FIG. 18  is an isometric cross-sectional view illustrating manufacture of the outer sleeve and outer support of the window component subassembly of  FIG. 15 . 
         FIG. 19  shows brazing induced strain produced as a result of manufacture of the outer sleeve and outer support of the window component subassembly of  FIG. 15 . 
         FIG. 20  is a cross-sectional view of an alternative embodiment of the window assembly in accordance with one aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Generally, in accordance with an aspect of the present invention, an electron beam system in accordance with various embodiments preferably employs cold electron emission technology to produce sheets of emitters deployed in a cylindrical geometry. The cathode is held in a vacuum by a grounded, sealed cylindrical housing and insulated from ground potential. The cylindrical housing is vacuum sealed, and can be equipped with an ion pump. A high voltage power supply accelerates emitted electrons in a radially inward direction towards the centerline of the cylindrical geometry. The electrons pass in vacuum through windows constructed of thin foil material (e.g., titanium or a titanium compound) preferably comprising a window assembly and emerge into a cylindrical region, for example, an application space where irradiation of matter or compounds contained in an air stream or other media flowing through the cylindrical region occurs. The cold electron emitting surfaces can be masked to provide electron emission from a series of sectors that are matched in shape and alignment with the windows though which the electrons are accelerated. Alternatively, the system can include a control grid with openings that are of matching size and shape and aligned with the windows through which the electrons pass into the cylindrical region. 
     Referring to the drawing figures,  FIG. 1  shows a cross-sectional view illustrating one embodiment of a system  10  in accordance with one aspect of the present invention. The system  10  comprises an electron beam generator preferably employing a cold electron emission source to produce discrete emitters of specific shape and size to inject energetic electrons radially inwardly into an inner cylindrical region  12  to irradiate flowing media passing through the inner cylindrical region. 
     As shown in  FIG. 1 , the system  10  comprises a first cylinder  14  and a coaxial second cylinder  15 , both of which are electrically grounded. An emitting cathode  16  is disposed in a vacuum and may be mounted to a grounded sheath  18  within the first cylinder  14 . The sheath  18  may be an insulative material such as epoxy, oil, or gas. The first cylinder  14  is attached to the outer surface of a duct  20  and surrounds the duct and other elements of the system. The cathode  16  is preferably a cold cathode emission device. The system  10  is vacuum-sealed, and is preferably equipped with an ion pump  22 . A high voltage power supply  24  is connected through the duct  20  to the cathode  16  and may also be connected to a control electrode or grid  26  to accelerate the emitted electrons in a radially inward direction toward the centerline of the cylindrical geometry. As shown in  FIG. 2 , insulators  30  are incorporated to provide mechanical support for the cathode  16  and the control grid  26 . Alternatively, the control electrode or grid  26  may be omitted. 
     Referring to  FIGS. 1 and 2 , the electrons pass from the vacuum through windows  28  constructed of thin material (e.g., titanium or a titanium compound) and emerge into the central cylindrical region  12  where irradiation occurs to the materials or compounds contained in an air stream or other media that flows in the axial direction of the cylinder. In the embodiment that comprises the control grid  26 , the windows  28  are aligned with slots in the control grid. In the alternative embodiment in which the control grid  26  is omitted, the windows  28  are aligned with masked emission areas of the cold cathode  16 . 
     The cold cathode emitter  16  is preferably packaged as a unit that contains the emitter, electron beam optical focusing elements that direct the electron beam onto the individual exit windows  28  that separate the vacuum from the cylindrical region  12 , and the control grid  26  with variable bias voltage that controls the magnitude of the beam injected into the cylindrical region. 
     A preferred embodiment of the system  10  is shown in  FIG. 3 . For example,  FIG. 3A  shows a system  10 A that is adapted to be incorporated into a standard 10-inch duct. Flanges  10 A 1  and  10 A 2  are sized for interconnecting the system  10 A in line with a 10-inch duct.  FIG. 3B  shows an exemplary system  10 B that is adapted to be incorporated into a standard 4-inch duct. Flanges  10 B 1  and  10 B 2  are sized for interconnecting the system  10 B in line with a 4-inch duct. Thus, the system  10  in accordance with the various embodiments is scalable to accommodate use in various fluid flow systems. 
     As shown in  FIGS. 3A and 3B , a nipple  22 A or  22 B is provided to connect to the ion pump  22  to draw a vacuum. Additionally, a high voltage connector  24 A or  22 B is provided to connect the control grid  26  and/or the cathode  16  to the high voltage power supply  24 . Additionally, a water cooling supply line and return line  40  may be provided, as shown in  FIG. 3B . 
       FIG. 4  is a detailed isometric cross-sectional view of the scalable system  10  shown in  FIG. 3 . The first cylinder  14  is defined by a cylindrical housing comprising end walls  14 A and  14 B and a cylindrical outer wall  14 C, that provides a shielded vacuum enclosure. The cylindrical housing  14 A,  14 B,  14 C is at ground potential. The ion pump  22  is connected to the nipple  22 A,  22 B and the duct  20  to the interior of the cylindrical housing  14 A,  14 B,  14 C to evacuate the interior of the cylindrical housing. The cathode  16  is preferably a segmented cold cathode constructed of carbon nanotube composite comprising carbon nanotubes vertically grown from a substrate. As shown in  FIGS. 4 and 5 , the segments  16 A of the cathode  16  are spaced apart and mounted on a cylindrical cathode support  42 .  FIG. 5  also shows the control grid  26  which comprises slots  26 A through which electrons emitted by the segments  16 A of the cathode  16  are accelerated. The control grid  26  may in turn be mounted to the cathode support  42  by the insulators  30 . Preferably, as shown in  FIGS. 4 and 5 , a focus grid  44  is provided to direct the electrons accelerated through the slots  26 A in the control grid  26  toward the windows  28 . In the alternative embodiment without a control grid, the focus grid  44  prevents scatter of electrons and forms an electron beam. 
     In accordance with an alternative embodiment, wire filament cathode elements are substituted for the segments of the carbon nanotube composite cathode shown in  FIG. 5 .  FIG. 6  is a detailed isometric cross-sectional view of the scalable system  10  shown in  FIG. 3  that illustrates the wire filaments  16 B of the cathode  16  spaced apart and mounted on the cylindrical cathode support  42 .  FIG. 6  also shows the control grid  26  which comprises the slots  26 A through which electrons emitted by the wire filaments  16 B of the cathode  16  are accelerated. Preferably, the focus grid  44  is provided to focus the electrons accelerated through the slots  26 A in the control grid  26 . In the alternative embodiment without a control grid, the focus grid  44  prevents scatter of electrons and forms an electron beam. 
     Referring again to  FIGS. 4 ,  5 , and  6 , the cathode  16 , control grid  26 , insulators  30 , and focus grid  44  are preferably mounted within a shielding enclosure  46  that provides a shield for sharp edges within the enclosure. The enclosure  46  is in turn mounted to the high voltage connector  24 A,  24 B within the duct  20 . The high voltage connector  24 A,  24 B is preferably a commercially available cone-shaped air-excluding type connector having a two-conductor to center ring connection configuration. One of the conductors is electrically connected to the cathode  16 , and the other conductor may be connected to the control grid  26 . 
     The high voltage power supply  24  is connected to the high voltage connector  24 A,  24 B. In accordance with one example, the high voltage power supply  24  supplies a relatively high negative voltage, for example, minus 160 kV to the cathode  16  and a relatively lower negative voltage, for example, minus 150 kV, to the control grid  26 . As is well understood by persons skilled in the art, the voltage applied to the control grid  26  by the high voltage power supply  24  can be varied to provide constant current operation. 
     As also shown in  FIG. 4 , the coaxial second cylinder  15  comprises a tube  15 A which is mounted within a through opening  14 D in the end walls  14 A and  14 B of the cylindrical housing. The tube  15 A is at ground potential. In accordance with one preferred embodiment, the tube  15 A comprises a stainless steel liner bonded to a copper sheath. The stainless steel liner resists corrosion due to contact with the flowing media. The copper sheath provides good thermal conduction to dissipate heat. In one example, the composite tube  15 A had a thickness of approximately 1 mm. 
       FIG. 4  also illustrates the windows  28  formed in the coaxial second cylinder  15 . In accordance with one embodiment, the windows  28  are constructed by first providing slits in the tube  15 A that are spaced apart and adapted to be aligned with the segments  16 A ( FIG. 5 ) or filaments  16 B ( FIG. 6 ) of the cathode  16 . Then, a titanium/aluminum foil is applied to the exterior of the tube  15 A overlying the slits and bonded to the tube by any of several methods known to persons skilled in the art. For example, the titanium/aluminum foil may be applied to the exterior of the tube  15 A overlying the slits and diffusion bonded to the tube. 
     In accordance with another aspect of the present invention, a window assembly may be provided in conjunction with the electron beam system shown in  FIGS. 1 and 4 . Referring to  FIG. 9 , a window assembly  110  may advantageously be substituted for the tube  15 A. The window assembly  110  has slits  122 A ( FIG. 15 ) comprising windows corresponding to the windows  28 , so that the electrons pass into the cylindrical region  12 . 
     Considered in more detail,  FIG. 9  is an isometric view of the window assembly  110  in accordance with one embodiment adapted to transmit radiation, for example, an electron beam, from an external source (not shown) to the cylindrical region  12 . The window assembly  110  preferably comprises a first end support subassembly  114  and a second end support subassembly  116 . The window assembly  110  also comprises a window component subassembly  118  disposed intermediate the first and second end support subassemblies  114 ,  116 . 
     The first end support subassembly  114  and second end support subassembly  116  are preferably similarly manufactured, but the first end support subassembly has a left-to-right orientation, while the second end support subassembly has a right-to-left orientation such that the first and second end support subassemblies shown in  FIG. 9  are mirror images of one another. Referring to  FIG. 10 , the first end support subassembly  114  comprises an end support  114 A shown in more detail in  FIG. 11 . The end support  114 A is preferably constructed from a metal having a relatively high coefficient of thermal expansion, for example, oxygen free electronic (OFE) grade copper having a coefficient of thermal expansion of 17.6×10 −6  cm/cm ° C. (9.8×10 −6  in/in ° F.). The end support  114 A has a first portion  114 A 1  having a given outside diameter and is preferably machined to provide a second portion  114 A 2  having a reduced outside diameter. 
     The first end support subassembly  114  also comprises an end sleeve  114 B, as shown in  FIG. 10 . As shown in more detail in  FIG. 12 , the end sleeve  114 B has a given inside diameter and is preferably constructed from a metal having a lower coefficient of thermal expansion than the end support  114 A. In the example in which the end support  114 A is constructed from OFE grade copper, the end sleeve  114 B may be constructed from 410S stainless steel, for example, having a coefficient of thermal expansion of 10.5×10 −6  cm/cm ° C. (5.9×10 −6  in/in ° F.). 
     The end support subassembly  114  is preferably manufactured as follows. The inside diameter of the end sleeve  114 B is larger than the outside diameter of the first portion  114 A 1  of the end support  114 A. A braze sheet  120 , for example, a copper-gold-nickel material, can be placed around the circumference of the first portion  114 A 1  of the end support  114 A, and the end sleeve  114 B can be slid onto the end support  114 A with the braze sheet disposed between the first portion  114 A 1  of the end support  114 A and the end sleeve  114 B, as shown in  FIG. 13 . The subassembly  114 A,  114 B and braze sheet  120  is then brazed at 780 degrees Centigrade, which produces the brazing induced strain shown in  FIG. 14 . The brazed subassembly is then preferably machined to remove any deformation (shown in  FIG. 14 ) resulting from brazing, and the end sleeve  114 B is machined to remove a portion of the end sleeve to expose a flange portion  114 A 1 X of the first portion  114 A 1  to produce the finished end support subassembly  114  shown in  FIG. 10 . 
     The second end support subassembly  116  preferably consists of similar components as the first end support subassembly  114  and is manufactured in a similar manner as the first end support subassembly, although the orientation is reversed to that of the first end support subassembly, as shown in  FIG. 9 . Accordingly, persons skilled in the art will readily understand the structure of the second end support subassembly  116  in view of the preceding description. 
     Referring now to  FIG. 15 , a window component subassembly  118  preferably comprises an additional cylinder comprising an inner sleeve  118 A. The inner sleeve  118 A has a given outside diameter and is preferably constructed from a titanium alloy, for example, having a coefficient of thermal expansion of 9.0 to 13×10 −6  cm/cm ° C. (4.9 to 7.1×10 −6  in/in ° F.). The inner sleeve  118 A is machined to provide a plurality of slits  122 A which comprise windows for radiation. 
     As shown in  FIG. 16 , the window component subassembly  118  further comprises an outer cylinder comprising an outer sleeve  118 B having a given inside diameter that is greater than the outside diameter of the inner sleeve  118 A and a given outside diameter. The outer sleeve  118 B is preferably constructed from a metal having a relatively high coefficient of thermal expansion, for example, OFE grade copper having a coefficient of thermal expansion of 17.6×10 −6  cm/cm ° C. (9.8×10 −6  in/in ° F.). 
     The window component subassembly  118  also preferably comprises an outer support  124  having a given inside diameter, as shown in  FIG. 18 . The inside diameter of the outer support  124  is larger than the outside diameter of the outer sleeve  118 B. A braze sheet  126 , for example, a copper-gold-nickel material, can be placed around the circumference of the outer sleeve  118 B, and the outer support  124  can be slid onto the outer sleeve  118 B with the braze sheet disposed between the outer sleeve  118 B and the outer support  124 , as shown in  FIG. 18 . The subassembly  118 B,  124  and braze sheet  126  is then brazed at 780 degrees Centigrade, which produces the brazing induced strain shown in  FIG. 19 . The brazed subassembly is then preferably machined to remove any deformation (shown in  FIG. 19 ) resulting from brazing. The brazed subassembly comprising the outer sleeve  118 B and outer support  124  is then machined to provide a plurality of slits  122 B which comprise windows for electromagnetic radiation. 
     As shown in  FIG. 17 , an inner cylinder comprises foil  118 C, for example, titanium alloy foil. The inner foil cylinder  118 C is preferably placed around the circumference of the inner sleeve  118 A so as to overlie the slits  122 A. The titanium alloy foil  118 C has a thickness of 1.0 mil. or less, for example. 
     The window component subassembly  118  is preferably manufactured as follows. As shown in  FIG. 15 , the titanium-alloy-film-wrapped inner sleeve  118 A,  118 C is slid into the outer sleeve  118 B so that the slits  122 A of the inner sleeve align with the slits  122 B of the outer sleeve and outer support  124 . The resulting subassembly  118 A,  124 ,  118 B,  118 C is slid into a tool  128 . 
     The manufacture of the window subassembly  110  can be completed as follows. A material, for example, silver, is deposited onto the exterior of the inner sleeve  118 A and the flange  114 A 1 X of the first end support subassembly  114  and the corresponding flange of the second end support subassembly  116 . The flange  114 A 1 X of the first end support subassembly  114  and the corresponding flange of the second end support subassembly  116  have an outside diameter that is less than the inside diameter of the inner sleeve  118 A, and are slid into the opposite ends of the inner sleeve disposed in the tool  128 . A tubular mandrill (not shown) having a higher coefficient of thermal expansion than the tool  128  is then inserted through the interior of the first and second end support subassemblies  114 ,  116  and the inner sleeve  118 A. The final window assembly  110  is then heated at approximately 450 degrees centigrade to form a diffusion bond between the first and second end support subassemblies  114 ,  116  and window component subassembly  118 . 
     Referring again to  FIG. 4 , the window assembly  110  is mounted within the through opening  14 D in the end walls  14 A and  14 B of the cylindrical housing  14 . The window assembly  110  is at ground potential. In accordance with one preferred embodiment, the OFE copper sleeves comprising the window assembly  110  provide good thermal conduction to dissipate heat. In one example, the window assembly  110  had a thickness of approximately 1 mm. The slits  122 A in the window assembly  110  comprising the windows corresponding to the windows  28  are adapted to be aligned with the segments of the cathode  16 . 
     High energy radiation passes through the slits  122 A, the foil  118 C constructed of thin material (e.g., titanium or a titanium compound such as a titanium/aluminum alloy), and slits  122 B comprising the windows corresponding to the windows  28  and emerges into the cylindrical region  12  where irradiation occurs, for example, to treat materials or compounds contained in an air stream or other media that flows in the axial direction of the cylinder. 
     As shown in  FIG. 4 , the interior of the tube  15 A or window assembly  110  forms the cylindrical region  12 . Radiation produced by the system  10  will flow from the input and output ends of the cylindrical region  12 , so a shield to prevent leakage is preferably provided to avoid exposure of personnel to radiation. In accordance with one embodiment, a helix or an auger of sufficient shielding capacity is inserted into each of the input and output openings to the cylindrical region  12 , but not within the region  12  itself. Accordingly, as shown in  FIG. 4 , a first shielding helix or auger  48 A is provided at an input end of the tube  15 A or window assembly  110 , and a second shielding helix or auger  48 B is provided at an output end of the tube or window assembly. In one example, the shielding helixes or augers  48 A,  48 B are constructed from stainless steel coated copper. The shielding helixes or augers  48 A,  48 B provide shielding to prevent radiation from escaping. Also, the helix or auger shielding increases turbulence in the cylindrical region  12 . 
     The edges of the shielding helixes or augers  48 A,  48 B are in contact or near contact with the inner walls at the input and output sections of the tube  15 A or window assembly  110  through which media flows. The media flows through the helix or auger in a spiral geometry. This method provides two advantages: a compact shield against escaping radiation; and a means to create turbulence of the media flow entering the cylindrical region  12  and bringing the flowing media closer to the maximum region of power deposition of the electron beam, located in a layer closer to the electron beam windows  28 . This aids the system design goal of providing uniform dose distribution (or beam power deposition) to all unit volumes of media flowing through the cylindrical region  12 , and improves overall system treatment efficiency. 
     In accordance with one contemplated modification, within the cylindrical region  12 , a modified helix or auger of smaller diameter leaving gaps between the walls at the input and output sections of the tube  15 A or window assembly  110  and helix or auger blades may additionally be provided to force the media flow close to the regions of maximum electron beam intensity, and provide local turbulence close to the electron beam windows  28 . The optimum form of such a partial helix or auger might depart from a pure helix or auger shape. 
     As shown in  FIG. 7 , the inwardly directed electron beam  32  provides a distinct advantage over unidirectional or outwardly directed beams for creating a uniform flux throughout the treatment space defined by the cylindrical region  12 . The electrons lose energy from collisions with the molecules entrained in the flowing media, so strength of the interaction of the electron beam and the flowing media decreases with distance from the window surface. Inwardly directed electron beams  32  combine as the energy decreases, and thus maintain greater flux density with distance from the window surface. 
     The inward direction of the electron beams  32  from the cylindrical structure comprising the cathode  16 , control grid  26 , and focus grid  44  mounted within the shielding enclosure  46  toward the smaller cylindrical structure comprising the tube  15 A or the window assembly  110  improves the transmission of electrons through the windows  28 . The electrostatic field intensity increases logarithmically to cause the beams to be focused to a smaller cross-section as they approach the windows  28 . Thus, fewer of the electrons strike the supporting structure where they are lost from the beams entering the cylindrical region  12 . 
     A preferred embodiment of the method in accordance with an aspect of the present invention is shown in  FIG. 8 , generally indicated by the numeral  50 . Flowing media is introduced into the cylindrical region  12 , as indicated by a step  52  shown in  FIG. 8 . During treatment in the system, the media flowing through the cylindrical region  12  is irradiated with electrons radially inwardly directed through the windows  28  into the treatment region, as indicated by a step  54  shown in  FIG. 8 . Preferably, turbulence is generated in the media flow in the cylindrical region  12  and/or the media is forced to flow close to the regions of maximum electron beam intensity, as indicated by a step  56  shown in  FIG. 8 . Also, shielding is preferably provided to prevent escape of radiation from the cylindrical region  12 , as indicated by a step  58  shown in  FIG. 8 . Subsequently, additional flowing media may be introduced into the cylindrical region  12  and treated, as indicated by the arrow from step  58  to step  52  shown in  FIG. 8 . 
     The geometry of inwardly directed electron rays injected into a cylindrical treatment volume provides a very uniform and intense dose across the volume and is uniquely adaptable to media flowing through stacks and pipes to treat waste gases from industrial processes and to sterilize air streams and destroy pathogens or used to destroy contaminants extracted from groundwater or soil. 
     For example, the variety of applications of radiation to control contaminants in air streams covers a large range of airflow rates. A cylindrical geometry in accordance with the various embodiments of the present invention is scalable to meet this variation in flow rates by defining the inner diameter of the cylindrical region  12  to provide the specified air flow requirement of low pressure drop (typically a few inches of water) through the system. The range of the electrons in air is determined by the energy imparted to the electrons by the high voltage applied to accelerate the electrons, so a high voltage power supply is appropriately specified. 
     In comparison to other electron beam devices designed for destruction of compounds in flowing media, the various embodiments in accordance with the present invention have the following features:
     1. Use of cold cathode technology makes practical the cylindrical design of the system;   2. A cold cathode electron emitter unit that focuses all emitted electrons to the beam exit window for the treatment volume is optimally efficient;   3. A cold cathode electron emitter with control grid for electron emission intensity can adjust electron beam intensity to beam strength required for a given application;   4. A cylindrical design makes simpler and less costly the scaling of system size for a wider range of applications;   5. Allows reduced physical size and construction costs;   6. Reduces weight due to smaller volume of shielding required;   7. Results in reduced operating costs compared to known devices having thermionic cathodes;   8. Use of helix or auger principle to shield input and output of tubular section also provides optimum flow patterns into and, in addition, within the electron beam treatment region of the system.   

     An alternative embodiment of the window assembly  110 ′ in accordance with the present invention is shown in  FIG. 20 . The window assembly  110 ′ comprises a core  202  preferably constructed from a metal having a relatively high coefficient of thermal expansion, for example, OFE grade copper having a coefficient of thermal expansion of 17.6×10 −6  cm/cm ° C. (9.8×10 −6  in/in ° F.). The core  202  is preferably machined to provide channels  204  that provide conduits for a cooling fluid, for example, water. 
     The window assembly  110 ′ also comprises an inner support  206  preferably constructed from 410S stainless steel in the example in which the core  202  is constructed from OFE grade copper. A braze sheet (not shown), for example, a copper-gold-nickel material, can be placed between the core  202  and the inner support  206 , and the subassembly  202 ,  206  and braze sheet can then be heated at 780 degrees Centigrade to braze the core to the inner support. The brazed subassembly is then preferably machined to remove any deformation resulting from brazing. The brazed subassembly comprising the core  202  and inner support  206  is also machined to provide a plurality of slits  208  which comprise windows for radiation. 
     As shown in  FIG. 20 , the window assembly  110 ′ also comprises an outer corrosion resistant shield  212  preferably constructed from 410S stainless steel in the example in which the core  202  is constructed from OFE grade copper. The outer shield  212  is machined to provide slits  214  which comprise windows for radiation. 
     Foil  210 , for example, titanium alloy foil, is placed against the surface of the core  202  opposite the surface of the core that is brazed to the inner support  206 , as shown in  FIG. 20 . The titanium alloy foil  210  has a thickness of 1.0 mil. or less, for example. 
     The manufacture of the window assembly  110 ′ can be completed as follows. A material, for example, silver, is deposited onto the titanium-film-covered core  202 . The outer shield  212  is then placed against the foil  210 , and the assembly is clamped together and heated at approximately 450 degrees centigrade to form a diffusion bond between the titanium-film-covered core  202  and the outer shield. 
     Radiation supplied by a source (not shown) passes though slits  208 , the foil  210 , and slits  214  comprising windows of the window assembly  110 ′. Nipples (not shown) can be connected between the channels  204  and a source of cooling fluid (not shown) to supply cooling fluid to the core  202  to dissipate heat. 
     While the foregoing description has been with reference to particular embodiments and contemplated alternative embodiments in accordance with the aspects of the present invention, it will be appreciated by those skilled in the art that changes in these embodiments may be made without departing from the principles and spirit of the invention. Accordingly, the scope of the present invention can only be ascertained with reference to the appended claims.