X-ray tube electron beam formation and focusing

摘要

X-ray tube electron beam focusing utilizing a cathode having a large cavity therein in which an electron cloud is generated and which is shielded from the primary electric field between the cathode and the anode. The electron cloud flows from the cavity through a small narrow passage and into the primary electric field. An opposed spaced apart pair of electrical grids each comprising an array of individual electrode segments have selected opposed segments electronegatively biased to change the cross-section of the passing electron stream therebetween. The altered cross-section of the electron stream determines the size of the focal spot of the electron beam impacting the target anode.