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An rf linear accelerator for producing an electron beam. The outer wall of the rf cavity of said linear accelerator being perforated to allow gas inside said rf cavity to flow to a pressure chamber surrounding said rf cavity and having means of ultra high vacuum pumping of the cathode of said rf lin

An rf linear accelerator for producing an electron beam. The outer wall of the rf cavity of said linear accelerator being perforated to allow gas inside said rf cavity to flow to a pressure chamber surrounding said rf cavity and having means of ultra high vacuum pumping of the cathode of said rf linear accelerator. Said rf linear accelerator is used to accelerate polarized or unpolarized electrons produced by a photocathode, or to accelerate thermally heated electrons produced by a thermionic cathode, or to accelerate rf heated field emission electrons produced by a field emission cathode.

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1. A compact, radio-frequency driven, electron linear accelerator having a longitudinal axis for producing an electron beam comprising: a plurality of cylindrical disks positioned inside a large cylindrical tank which is capped at either end with an end plate; said disks being supported by a plurali

1. A compact, radio-frequency driven, electron linear accelerator having a longitudinal axis for producing an electron beam comprising: a plurality of cylindrical disks positioned inside a large cylindrical tank which is capped at either end with an end plate; said disks being supported by a plurality of cooling rods that are suspended between said end plates;means for applying high-frequency rf power to said tank and converting the rf power to an electric field along the longitudinal axis of the said disks;a cathode located at the center of one of said end plates, capable of producing electrons that are accelerated through said accelerator;magnet focusing system positioned in operative relationship to said accelerator for focusing the charged electron beam; anda plurality of longitudinal slots through the outer wall of the rf cavity of said accelerator; and means of ultra high vacuum pumping of said cathode through said longitudinal slots. 2. The linear accelerator of claim 1 wherein the rf cavity of said accelerator is a plane wave transformer. 3. A compact, radio-frequency driven, electron linear accelerator having a longitudinal axis for producing an electron beam comprising: a ½-cell rf cavity with no cooling rods inside said cavity; said cavity comprising an outer region and an inner region; said outer region of the said cavity supporting a TEM-like mode and said inner region of said cavity supporting a TM-like mode;means for applying high-frequency rf power to said tank and converting the rf power to an electric field along the longitudinal axis of the said rf cavity;a cathode located at the center of one of one of the end plates of said rf cavity, capable of producing electrons that are accelerated through said accelerator;magnet focusing system positioned in operative relationship to said accelerator for focusing the charged electron beam; anda plurality of longitudinal slots through the outer wall of the rf cavity of said accelerator;and means of ultra high vacuum pumping of said cathode through said longitudinal slots. 4. The linear accelerator of claim 1 or claim 3 wherein said rf cavity comprising two concentric regions, the outer region having a longer length than the inner region which has an active acceleration length of approximately one-quarter of the rf wavelength. 5. The linear accelerator of claim 3 wherein said rf cavity is a hybrid mode cavity. 6. The linear accelerator of claim 1 or claim 3 wherein said rf cavity is surrounded by a pressure vessel in which a getter material is used to provide ultra high vacuum pumping. 7. The linear accelerator of claim 1 or claim 3 wherein said rf cavity is surrounded by a pressure vessel that is connected to an ion pumping to provide ultra high vacuum pumping. 8. The cathode in claim 7 being made of semiconductor material such as Gallium Arsenide, capable of producing a polarized electron beam when illuminated by a polarized laser beam. 9. The linear accelerator of claim 7 further including a load lock to maintain a high vacuum condition within said tube. 10. The linear accelerator of claim 1 or claim 3 wherein said rf cavity is surrounded by a pressure vessel in which a large, low temperature surface is used to provide ultra high vacuum pumping. 11. The linear accelerator of claim 1 or 3, wherein said cathode is a photocathode that can generate pulsed electrons upon illumination by a pulse laser beam. 12. The linear accelerator of claim 1 or 3, wherein said cathode being a thermionic cathode that can be heated externally to generate an electron beam to be accelerated in said linear accelerator. 13. The linear accelerator of claim 1 or 3, wherein said cathode being a field emission cathode that can be heated by the rf field at the surface of said cathode to extract an electron beam from said cathode to be accelerated in said linear accelerator.