Abstract:
An electron gun includes the following: a primary thermionic electron source, a secondary thermionic electron source and a focusing electrode disposed within a first housing that includes one or more reference members adjustably attached to a housing support connected to a first platform; an anode and one or more focusing coils disposed within a second housing comprising one or more insulating members adjustably connected to the first platform; and one or more deflection coils disposed within a third housing connected to the second housing and located opposite said first housing.

Description:
FIELD OF USE  
       [0001]     This invention relates to an electron gun and, more particularly, to an electron gun having two thermionic electron sources.  
       BACKGROUND OF THE INVENTION  
       [0002]     Electron beam furnaces and coaters are used to heat materials to produce vapors for deposition on an article. An electron beam furnace includes an electron gun, a deflection system, and a cooling system. The electron gun generates an electron beam. The deflection system directs the electron beam toward the material to be heated. The cooling system cools the electron gun to prevent it from overheating.  
         [0003]     An electron gun typically includes an electron source, a focusing electrode, and an accelerating electrode. The electron source is typically a cathode heated by an electric current to cause the cathode to emit electrons. The focusing electrode is typically negatively charged to repel the electrons and thereby direct the electrons in a direction generally toward the accelerating electrode. The accelerating electrode is typically less negatively charged than the electron source and the focusing electrode to cause the electrons to form into a beam and travel in the downstream direction.  
         [0004]     In one known type of electron gun, the electron source and the focusing electrode are elongated and disposed in a head. The head is supported by a platform spaced apart from the accelerating electrode. This type of electron gun is reliable and available in many different power ratings. The physical size of the head, the accelerating electrode, and the platform of a given one of these electron guns depends on its power rating.  
         [0005]     During operation the electron beam generates ions, the ions move in the reverse direction relative to the motion of the electrons and accelerate in the electric field between the cathode and anode. As these high energy ions strike the cathode surface, the ions cause the cathode material to diffuse and vaporize. The cathode eventually deforms due to constant reflected electron bombardment and erodes away. Cathode deformation also impacts the performance of the electron gun. The evaporation rate of the electron gun becomes altered. As a result, the average life and overall useful life of the electron gun becomes significantly reduced. In turn, one&#39;s ability to coat a requisite number of targets in assembly is hampered and overall productivity is significantly affected.  
         [0006]     Consequently, there exists a need for an electron gun assembly constructed to increase service and active life of the electron gun as well as permit the quick and efficient replacement of the thermion source without restricting the power rating of the electron gun.  
       SUMMARY OF THE INVENTION  
       [0007]     In accordance with the present invention, an electron gun broadly comprises a primary thermionic electron source, a secondary thermionic electron source and a focusing electrode disposed within a first housing broadly comprising one or more reference members adjustably attached to a housing support connected to a first platform; an anode and one or more focusing coils disposed within a second housing broadly comprising one or more insulating members adjustably connected to the first platform; and one or more deflection coils disposed within a third housing connected to the second housing and located opposite the first housing.  
         [0008]     In accordance with the present invention, a method for using an electron gun broadly comprises heating a primary thermionic electron source; emitting a first electron beam from the primary thermionic electron source through a first electric field; striking a secondary thermionic electron source with the first electron beam; heating the secondary thermionic electron source; emitting a second electron beam from the secondary thermionic electron source; accelerating the second electron beam through a second electric field; focusing the second electron beam through a focusing electrode; passing the second electron beam through an accelerating anode; focusing the second electron beam through one or more magnetic fields; deflecting the second electron beam through one or more magnetic fields; and striking a target with the second electron beam.  
         [0009]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a representation of a cross-sectional view of the second housing and third housing of an axial electron gun of the present invention;  
         [0011]      FIG. 2  is a representation of a cross-sectional view of the first housing of the axial electron gun of  FIG. 1 ; and  
         [0012]      FIG. 3  is a graph comparing the thermionic electron source (or cathode life) of the axial electron gun of the present invention to a first generation linear electron beam gun and a second generation linear electron beam gun of the prior art. 
     
    
       [0013]     Like reference numbers and designations in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0014]     The axial electron gun of the present invention incorporates two thermionic electron sources. Upon heating a primary thermionic electron source, the primary thermionic electron source emits a flow of electrons which bombards a secondary thermionic electron source causing its heating. The electrons within the beam accelerate and obtain energy within electric fields of opposing potentials generated by the primary and secondary thermionic electron sources. The acceleration of electrons within the electric field causes the electrons to align and form an electron beam with the aid of the focusing electrode. The focusing electrode directs the electron beam into an aperture of an accelerating anode aligned in a direct line-of-sight with the secondary thermionic electron source. The electron beam continues accelerating as it passes the anode and enters within range of magnetic fields generated by a set of focusing coils and a set of deflection coils. The two sets of coils are capable of generating magnetic fields having sufficient intensity to deflect the electron beam vertically and horizontally and further focus the electron beam. Depending on a direction and intensity of this field, the electron beam deflects in the required direction. The resultant electron beam may be utilized to heat objects and even perform scanning operations.  
         [0015]     The electron gun of the present invention is an axial electron gun capable of mounting to existing electron beam physical vapor deposition equipment due to its compact size and versatile nature. The axial electron gun  10  generally comprises a first housing  12 , or a thermionic electron source assembly, a second housing  14 , or an electron beam focusing assembly, and a third housing  16 , or an electron beam control module. Components of the electron beam control module may also be found within the electron beam focusing assembly.  
         [0016]     The present axial electron gun employs one or more means for adjusting. The means for adjusting may generally be described as any type of adjustable implement that can secure two or more parts together and then release, if necessary, to disassemble the parts. Suitable adjustable implements may include, but are not limited to, screws, bolts, nuts, clamps, and the like. Likewise, the channels through which these means for adjusting are inserted may be possess the necessary complimentary facial indicia to mate, if necessary, with the means for adjusting. Representative facial indicia may include, but is not limited to, grooves, smooth bore, chamfered surfaces, tapered surfaces, combinations comprising at least one of the foregoing facial indicia, and the like. The present axial electron gun also employs one or more means for securing. The means for securing may generally be described as any type of securable implement that can secure two or more parts together and then release, if necessary, to disassemble the parts. Suitable securable implements may include, but are not limited to, screws, bolts, nuts, clamps, and the like.  
         [0017]     Referring now to  FIGS. 1 and 2 , the thermionic electron source assembly of first housing  12  may be connected to second housing  14  by one or more high voltage insulators  11 . High voltage insulators  11  may be disposed through one or more apertures  13  of a plate  15  of first housing  12 . Apertures  13  are designed to threadingly receive high voltage insulators  11 . Plate  15  also includes an aperture  17  and an adjustment flange  19  through which the thermionic electron source assembly is disposed there through and adjustably positioned. High voltage insulators  11  may be secured to second housing  14  using a means for securing  21  attached to a ledge  23  of second housing  14 . Second housing  14  may be detachably connected to third housing  16  using one or more second means for securing  25 . For purposes of illustration, high voltage insulators  11  may be enclosed within a separate housing, for example, a cylindrical housing with a cap affixed on top in order to prevent exposure to dusting from the metal vapor deposition process.  
         [0018]     First housing  12  ( FIG. 2 ) of axial electron gun  10  may comprise a false trap  18  disposed within a false trap holder  20 . For purposes of illustration, false trap holder  20  may include a ledge  22  or other means for supporting false trap  18 . False trap holder  20  may further include a lip  24  designed to be supported by an insulator  26 . Insulator  26  may comprise a single solid part or two halves that attach together. Insulator  26  connects to form an aperture designed to receive false trap holder  20 . A first means for adjusting  28  may be disposed within one or more first channels  30  formed within insulator  26  and false trap holder  20  and hold false trap holder  20  firmly in place within insulator  26 . Insulator  26  may be further disposed about a filament holder  32 . Filament holder  32  may be a single solid part or comprise two halves that combine together. Filament holder  32  may be secured firmly in place within insulators  26  by a second means for adjusting  34  disposed within one or more second channels  36  formed within insulator  26  and filament holder  32 . One or more electrical terminals  52  are preferably connected to second means for adjusting  34 , and one or more shielding apparatus  54  may be disposed between electrical terminals  52  and second means for adjusting  34 . Shielding apparatus  54  are designed to protect insulator  26  of axial electron gun  10  against dusting created by the metal vapor deposition process. The false trap holder  20 , insulator  26  and filament holder  32  combine to form and define a gun chamber  50  within first housing  12 .  
         [0019]     At least a portion of filament holder  32  is inserted within a thermal barrier enclosure  38  of first housing  12 . Within thermal barrier enclosure  38 , a clamp  40  may be disposed about filament holder  32 . Clamp  40  may be a single solid part or comprise two halves that combine together. Clamp  40  and filament holder  32  may combine to form a cavity  42  designed to receive a primary thermionic electron source  44 . Filament holder  32  may also be secured firmly in placed within clamp  40  by a third means for adjusting  46  disposed within one or more third channels  48  formed within filament holder  32  and clamp  40 .  
         [0020]     Primary thermionic electron source  44  may be disposed within cavity  42  and through a first thermal shield  54  and a second thermal shield  56 . Preferably, primary thermionic electron source  44  is a filament coil circumferentially disposed between filament holder  32  and clamp  40 . Suitable filament coils may comprise any suitable material for use in an electron gun that is capable of emitting electrons when heated such as, but not limited to, tungsten and the like. First thermal shield  54  may comprise a plurality of thermal shield plates having apertures designed to permit insertion of primary thermionic electron source  44  therethrough. Likewise, second thermal shield  56  may also comprise an aperture designed to permit insertion of primary thermionic electron source  44  therethrough. Second thermal shield  56  is preferably disposed in contact with and below first thermal shield  54 . Primary thermionic electron source  44  is preferably disposed opposite a secondary thermionic electron source  58 .  
         [0021]     Secondary thermionic electron source  58  may be disposed within one or more adjustable rings  60  and further disposed within a focusing electrode  62  secured to thermal barrier enclosure  38 . Adjustable rings  60  are preferably designed to accommodate and secure secondary thermionic electron source  58  within focusing electrode  62 . Secondary thermionic electron source  58  may also be supported by a ledge  66  of focusing electrode  62 . Focusing electrode preferably includes an aperture  70  through which secondary thermionic electron source  58  is disposed through and a planar surface  72  of source  58  is in a direct line of sight to secondary housing  14 . Secondary thermionic electron source  58  may comprise a substantially cylindrical shape having a circumferentially disposed lip  64  about a planar surface of source  58 . Circumferentially disposed lip  64  is preferably in contact with ledge  66  such that secondary thermionic electron source  58  may be suspended within aperture  70  of focusing electrode  62 . A plate  68  may be disposed in contact with and on top of both secondary thermionic electron source  58  and focusing electrode  62  to firmly secure both components within thermal barrier enclosure  38 .  
         [0022]     Secondary thermionic electron source  58  may comprise any suitable material for use in an electron gun that is capable of emitting electrons when heated such as, but not limited to, tungsten and the like. Preferably, primary thermionic electron source  44  and secondary thermionic electron source  58  comprise the same material.  
         [0023]     The electron beam focusing assembly of second housing  14  includes a depressed area  74  where an accelerating anode  78  having a substantially frustoconical shape comprising an aperture  76  may be disposed therein. Frustoconical projection  75  may be secured in place by a plate  77  and a fifth means for adjusting  80  disposed thereupon within depressed area  74 . Aperture  76  is preferably aligned in a direct line-of-sight with secondary thermionic electron source  58 . An accelerating anode  78  is preferably positioned and aligned in a direct line-of-sight with secondary thermionic electron source  58 . A pair of focusing coils  86 A,  86 B may be disposed within second housing  14  such that each focusing coil  86 A and  86 B are aligned parallel to electron beam chamber  82  and receive power via a power connection  94 . Surrounding each focusing coil  86 A,  86 B are a plurality of cooling channels  88  designed to carry a cooling fluid flow and prevent coils  86 A and  86 B from overheating during use of axial electron gun  10 . A cooling fluid reservoir (not shown) may be connected to axial electron gun  10  using one or more cooling fluid hoses  90  and  92  to deliver cooling fluid to the axial electron gun  10 . Focusing coils  86 A,  86 B and cooling channels  88  are preferably protected from electron scattering and contamination by a thermal shielding material  95 .  
         [0024]     The electron beam control module of third housing  16  may be disposed in contact with and below second housing  14 . Third housing  16  may comprise a base  96  and a pair of sidewalls  98  integrally disposed to base  96 . Sidewalls  98  extend to form both a cooling channel  100  and a cradle structure  102  designed to accommodate a pair of deflection coils  104 A,  104 B attached to power connection  94 . Cradle structure  102  includes an edge  106  integrally formed therein and designed to be supported by an exterior wall  108  of base  96 . A thermal shield  110  having an aperture  112  may be disposed upon deflection coils  104 A,  104 B, cradle structure  102  and sidewalls  98 . Thermal shield  110  may be connected to cradle structure  102  by a sixth means for adjusting  114  in order to protect deflection coils  104 A,  104 B from scattered electrons and contamination. Thermal shield  110  and sidewalls  98  combine to form and define an electron beam chamber  116  of axial electron gun  10 . Electron beam chamber  116  is preferably aligned with in a direct line-of-sight with electron beam chamber  82  of second housing  14 . Third housing  16  of axial electron gun  10  may be secured to an existing structure using any number of means for securing as discussed earlier and known to one of ordinary skill in the art.  
         [0025]     Focusing coils  86 A,  86 B and deflection coils  104 A,  104 B may comprise magnets and, preferably, ring-type 12-pole magnetic circuits combined with the coils. The magnetic circuits, coils and housing  12 ,  14  and  16  are all under “ground” potential. Focusing coils  86 A,  86 B and deflection coils  104 A,  104 B are each wound together, respectively, in groups of two and connected in series such that the beginning of one wound coil  86 A, for example, the north pole, is connected to the end of another wound coil  86 B, for example, the south pole. Either focusing coils,  86 A and  86 B or deflection coils  104 A and  104 B, generate magnetic fields capable of vertically deflecting an electron beam while the other set of focusing coils,  104 A and  104 B or  86 A and  86 B, generates magnetic fields capable of horizontally deflecting the electron beam.  
         [0026]     High potential circuits may be utilized for filament current circuits, bombardment circuits and accelerating voltage circuits for axial electron gun  10 . Low potential circuits may be utilized as power supply circuits for both deflection coils and magnets and focusing coil and magnets. The operating power of axial electron may be expressed by multiplication of a beam current by accelerating voltage. The power of axial electron gun  10  may be adjusted through the change of filament current of the primary thermionic electron source  44  for the change of bombardment current of the secondary thermionic electron source  58 , that is, through the change of temperature of source  58 .  
         [0027]     During operation, a filament current of about 1 ampere (A) to 80 A, and more particularly about 5 A to 70 A, and preferably about 10 A to 60 A may be applied through electrical terminals  52  through insulators  26  and to the filament coil of primary thermionic electron source  44 . Primary thermionic electron source  44  generates a thermionic particle cloud, for example, an electron cloud, whose electrons align within the electric field generated by the current application through the primary thermionic electron source  44 . These electrons are directed toward, bombard and heat secondary thermionic electron source  58  to generate another thermion particle cloud. The bombardment voltage may be approximately 0.5 kilovolts (kV) to 2.5 kV, and more particularly about 1.0 kV to 2.0, and preferably 1.5 kV. The bombardment current may be adjusted, if necessary, up to about 1 A. Secondary thermionic electron source  58  is also charged by the current to possess an opposite potential, for example, negative potential, relative to both primary thermionic electron sources  44  to create another electric field of opposite potential. The accelerating voltage of the electric field may be about 5 kV to 45 kV, and more particularly about 10 kV to 35 kV, and preferably about 17 kV to 25 kV. As the electron beam passes through the electric fields of opposite potential the electrons accelerate. The thermions, or electrons, are aligned within the electric field and directed by focusing electrode  62  towards accelerating anode  78  as an electron beam (not shown).  
         [0028]     As the electron beam passes through accelerating anode  78 , the electrons enter magnetic fields generated by focusing coils  86 A,  86 B and deflection coils  104 A,  104 B. A total current of about 0.1 A to 2 A, and more particularly about 0.5 A to 1.5 A, and preferably 1 A may be applied to focusing coils  86 A,  86 B. A total current of about 1 A to 5 A, and more particularly about 2 A to 4 A, and preferably about 3 A may be applied to deflection coils  104 A,  104 B. The application of varying currents generates magnetic fields that permit the operator of the axial electron gun  10  to deflect the electron beam at an angle of about 5 degrees (°) to 35°, and more particularly about 10° to 30°, and preferably about 20° in order to perform scanning operations using the electron beam.  
         [0029]     The axial electron gun of the present invention has many advantages over existing flat beam electron gun designs currently available. Referring to  FIG. 3 , a graph illustrates and compares the useful life of a first generation linear electron beam gun (A) to a second generation linear electron beam gun (B) to the axial electron gun of the present invention (C). Second generation linear electron beam guns overcame certain disadvantages of first generation linear electron beam guns to which second generation linear electron beam guns provided an increase of approximately 22.9% over their average life. The actual life of the present axial electron gun provides an increase of approximately 55% percent over the average life of second generation linear electron beam guns which translates into an actual life of approximately 100%. This significant improvement is due to the present axial electron gun utilizing both a primary thermionic electron source and a secondary thermionic electron source.  
         [0030]     During operation, electrons reflect off of the intended target and travel backwards through the gun chamber. These reflected electrodes strike surfaces throughout the gun chamber&#39;s interior including the thermionic electron source. In contrast to the present axial electron guns, current electron guns only employ one thermionic electron source that is continuously exposed to reflected electrons. As a result, the thermionic electron source deforms due to constant reflected electrode bombardment and eventually erodes away. This causes the electron beam gun to experience a diminished scanning frequency and changes the evaporation rate of the electron beam gun. In the present axial electron gun, the secondary thermionic electron source possesses a large mass (as compared to the primary thermionic electron source) and acts not only as a source of electrons but also as a target for reflected electrons. Continuous exposure to these reflected electrons will eventually deform and erode the secondary thermionic electron source; however, the primary thermionic electron source will continue operating without experiencing erosion. The resultant design incorporating two thermionic electron sources increases the active life (and average life) of the axial electron gun as compared to currently existing electron gun models, as documented in  FIG. 3 . Moreover, the present axial electron beam gun experiences a stabilized evaporation rate and an increased scanning frequency. For practical purposes, this increase in its active life translates into the present axial electron gun&#39;s ability to effectively double the amount of targets able to be coated during its use.  
         [0031]     Secondly, the necessity to replace an electron gun in an existing electron beam coating apparatus spurred the concept behind the present axial electron gun. The inventors of record sought to replace an old model electron beam gun only to discover the newer model electron beam gun was massive in size and measured at least three feet long. Unfortunately, the newer model&#39;s size prevented its use in the existing apparatus. As a result, the present axial electron beam gun has a compact design and preferably measures approximately 240 millimeters (9.45 inches) in height and 200 millimeters (7.87 inches) in diameter. It is also contemplated that the dimensions can be altered while maintaining the novel design features. For example, the present axial electron beam gun height may be from approximately 200 millimeters (7.87 inches) to 400 millimeters (15.75 inches) and the diameter may be from approximately 150 millimeters (5.91 inches) to 300 millimeters (11.8 inches). The compact design of the present axial electron gun makes the overall footprint of the entire gun assembly smaller than most electron beam guns currently available yet provides power equivalent to larger assemblies while also possessing a much longer useful life. The compact design also permits the present axial electron beam gun to be fitted to many, if not all, commercially available electron beam coating apparatus. As illustrated in  FIG. 1 , the axial electron gun may be mounted to an existing structure using any number of methods, for example, screwed, bolted, riveted, punched, clamped and the like.  
         [0032]     Thirdly, the present axial electron beam gun also provides significant cost benefits over other commercially available electron guns. It is estimated that the present axial electron beam gun may cost approximately $60,000.00 to $100,000.00 for the entire apparatus. In contrast, existing commercially available electron guns cost approximately $400,000.00 to $500,000.00. And, these existing commercially available electron guns do not possess the design advantages and average useful life demonstrated by the present axial electron gun. Moreover, as experienced by the inventors of record, certain commercially available electron guns cannot be utilized broadly for existing commercially available electron beam coating apparatus to the significant difference in size.  
         [0033]     Lastly, the present axial electron beam gun may also be assembled by a single person using common tools. None of the parts are too heavy for one person to lift and piece together. And, in addition, most parts either fit within each other or are secured to one another using screws, bolts and other means for adjusting as described herein. Consequently, an operator may quickly assemble the present axial electron gun using a variety of wrenches and screwdrivers to connect the parts.  
         [0034]     It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible to modification of form, size, arrangement of parts, and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.