Chicane magnet focusing system and deflection magnet for a scanning electron beam computed tomography system

摘要

Tuning, integrating, and operating an electron beam CT scanning system is simplified by using the fringe field from dipole magnets arranged as a chicane to focus the electron beam, thus replacing conventional quadrupole and solenoid coils. Preferably four "chicane" dipole magnets are series-coupled with the windings in the downstream deflection magnet, such that the chicane magnet X and Y coils are energized 90° out of phase with the deflection magnet coils. The alternating current polarity in the chicane magnets creates an "S"- shaped electron beam trajectory that adequately uniformly focuses over the full cross-section of the electron beam. Winding the coils with a cosine distribution permits rotating the magnetic fields to change the azimuthal and deflecting planes of the electron beam, without disturbing the deflection angle and focusing properties. Chicane electrical current directions and magnet positions are such that the electron beam enters and exists the chicane on the axis of the scanning electron beam CT system. A new type of deflecting magnet is provided that has no end windings, and may be used in other beam optical systems.