Patent ID: 6160869
Filing Date: 2000-12-12
Classification: H01J

Abstract:
A system for focusing an electron beam spot upon an X-ray emitting target in a scanning electron beam CT X-ray system that includes an electron gun mounted within a vacuum housing chamber that has an upstream region, commencing with said electron gun, wherein the electron beam expands and has a downstream region, terminating at said X-ray emitting target, wherein the electron beam converges to form the beam spot, the system for focusing comprising:a deflecting magnet having an X-axis deflecting coil winding and a Y-axis deflecting coil winding, disposed on a Z-axis projecting through said vacuum housing chamber at a downstream region of said X-ray system;a chicane assembly of dipole magnets, disposed coaxially with and upstream from said deflecting magnet, each of said dipole magnets having an X-axis dipole coil winding coupled in series with said Y-axis deflecting coil winding, and having a Y-axis dipole coil winding coupled in series with said X-axis deflecting coil winding;said X-axis deflecting coil winding and said Y-axis dipole coil windings being coupleable to a first source of current, and said Y-axis deflecting coil winding and said X-axis dipole coil windings being coupleable to a second source of current;adjacent ones of said X-axis dipole coil windings being configured as to alternate polarity of electrical current passing therethrough responsive to said second source of current, and adjacent ones of said Y-axis dipole coil windings being configured as to alternate polarity of electrical current passing therethrough responsive to said first source of current;wherein said dipole magnets create a magnetic field focusing said electron beam on said X-ray emitting target; andwherein operation of said system in potentially dangerous beam profile regimes is avoided.