Electron beam gun with grounded shield to prevent arc down

Abstract

A grounded metallic shield which comprises an electrode enclosing the filament leads and emitters of an e-Gun in a high vacuum chamber of the type used in melting and casting metals and other materials and evaporation sources. The shield is spaced from the filament leads and emitters a distance in the order of the electron mean free path for the pressure uses within the high vacuum chamber. The structure and method of use thereof suppresses or eliminates arc-downs or glow discharges.

What is claimed is: 
     
       1. In an electron beam gun within a high vacuum chamber subjected to a pre-selected vacuum, a plurality of high voltage surfaces, a metallic shield surrounding all of said high voltage surfaces, means grounding said shield, said shield being spaced from said surfaces a distance less than the mean free path of electrons at said pre-selected vacuum, said high voltage surfaces comprising filament leads and an emitter structure connected through said filament leads to a high voltage source external to said chamber, said shield being formed with a small hole in the path of electrons from said emitter to a target in said vacuum chamber, a crucible, and means to focus and direct the path of electrons from said emitter structure to said crucible over an arc passing through said small hole. 
     
     
       2. The chamber of claim 1 in which said filament leads comprise rods and said shield comprises at least one tube in co-axial relation to said rods. 
     
     
       3. The chamber of claim 1 in which said shield comprises sheets substantially enclosing said emitter. 
     
     
       4. The chamber of claim 1 in which said shield is formed with slits to permit vacuum pump-out of said shield. 
     
     
       5. The chamber of claim 1 in which said path of electrons is over an arc of approximately 270°. 
     
     
       6. The chamber of claim 1 in which said path of electrons is over an arc of approximately 180°. 
     
     
       7. In combination, means including a wall to form a vacuum chamber, a crucible shaped with a hollow suitable for containing a target material, means for subjecting said chamber to a pre-selected vacuum, a plurality of high voltage feed-ins leading from an external high voltage source through said wall into said chamber, a feedthrough for said feed-ins, filament leads connected to said feed-ins, an emitter structure connected to said filament leads, and a metallic shield grounded relative to said crucible surrounding said filament leads, said emitter structure, said feedthrough and all other high voltage surfaces within said chamber other than said crucible, said shield being spaced from said filament leads, from said emitter structure and said feedthrough a distance less than the mean free path of electrons at said pre-selected vacuum, said shield being formed with a small hole in the path of electrons from said emitters to said target material, and beam directing means to focus and direct said path of electrons in an arcuate path from said emitter structure through said small hole and into said hollow of said crucible. 
     
     
       8. The combination of claim 7 in which said shield is formed with slits to permit vacuum pump-out within said shield by said means for subjecting said chamber to a pre-selected vacuum for melting or evaporation of said target material. 
     
     
       9. The combination of claim 7 in which said shield comprises at least one tube in co-axial relation to said filament leads. 
     
     
       10. The combination of claim 7 in which said shield comprises metallic sheets substantially enclosing said emitter structure. 
     
     
       11. The combination of claim 9 in which said emitter structure and said crucible are positioned relative to said small hole so that the path of electrons from said emitter structure into said crucible is over an arc of approximately 180°. 
     
     
       12. The combination of claim 9 in which said beam directing means comprising a plurality of magnets in said chamber, said path of electrons from said emitter structure into said crucible being over an arc of approximately 270°. .Iadd. 
     
     
       13.  In an electron beam gun within a high vacuum chamber subject to a preselected vacuum, a plurality of high voltage surfaces, a metallic shield surrounding all of said high voltage surfaces, means maintaining said shield at a substantially different voltage than said plurality of high voltage surfaces, said shield being spaced from said surfaces a distance less than the mean free path of electrons at said pre-selected vacuum, said high voltage surfaces comprising filament leads and an emitter structure connected through said filament leads to a high voltage source external to said chamber, said shield being formed with a small hole in the path of electrons from said emitter to a target in said vacuum chamber, a crucible, and means to focus and direct the path of electrons from said emitter structure to said crucible over an arc passing through said small hole. .Iaddend. .Iadd.14. In a combination, means including a wall to form a vacuum chamber, a crucible shaped with a hollow suitable for containing a target material, means for subjecting said chamber to a pre-selected vacuum, a plurality of high voltage feed-ins leading from an external high voltage source through said wall into said chamber, a feedthrough for said feed-ins, filament leads connected to said feed-ins, an emitter structure connected to said filament leads, and a metallic shield maintained at a substantially different voltage relative to said high voltage feed-ins surrounding said filament leads, said emitter structure, said feedthrough and all other high voltage surfaces within said chamber other than said crucible, said shield being spaced from said filament leads, from said emitter structure and said feedthrough a distance less than the mean free path of electrons at said pre-selected vacuum, said shield being formed with a small hole in the path of electrons from said emitters to said target material, and beam directing means to focus and direct said path of electrons in an arcuate path from said emitter structure through said small hole and into said hollow of said crucible. .Iaddend. .Iadd.15. In an electron beam gun within a high vacuum chamber subjected to a pre-selected vacuum, a plurality of high voltage surfaces, a metallic shield surrounding all of said high voltage surfaces, means maintaining said shield at a voltage substantially less than that of said high voltage surfaces, said shield being spaced from said surfaces a distance less than the mean free path of electrons at said pre-selected vacuum, said high voltage surfaces comprising filament leads and an emitter structure connected through said filament leads to a high voltage source external to said chamber, said shield being formed with a small hole in the path of electrons from said emitter to a target in said vacuum chamber, a crucible, and means to focus and direct the path of electrons from said emitter structure to said crucible over an arc passing through said small hole. .Iaddend. .Iadd.16. In combination, means including a wall to form a vacuum chamber, a crucible shaped with a hollow suitable for containing a target material, means for subjecting said chamber to a pre-selected vacuum, a plurality of high voltage feed-ins leading from an external high voltage source through said wall into said chamber, a feedthrough for said feed-ins, filament leads connected to said feed-ins, an emitter structure connected to said filament leads, and a metallic shield maintained at a voltage substantially less than that of said filament leads, said metallic shield surrounding said emitter structure, said feedthrough and all other high voltage surfaces within said chamber other than said crucible, said shield being spaced from said filament leads, from said emitter structure and said feedthrough a distance less than the mean free path of electrons at said pre-selected vacuum, said shield being formed with a small hole in the path of electrons from said emitters to said target material, and beam directing means to focus and direct said path of electrons in an arcuate path from said emitter structure through said small hole and into said hollow of said crucible. .Iaddend.