MAGNETIC CIRCUIT FOR MAGNETIC FIELD LENS

摘要

PROBLEM TO BE SOLVED: To provide a compact magnetic circuit for a magnetic field lens for providing strong magnetic field intensity. SOLUTION: The magnetic circuit includes a magnet unit 11 having a center hole 17 through which an electron beam penetrates in the vertical direction and formed into almost a spherical shape around the center hole 17. The magnet unit 11 consists of: a pair of truncated cone-shaped main magnet members 12 and 16 having the magnetization direction same as that of the optical axis of the electron beam and arranged so that their top portions face each other; a plurality of auxiliary magnet members 13, 14 and 15 each arranged around each of the truncated cone-shaped main magnet members and having magnetization direction different from that of the adjacent magnet member; and a pole piece 19 fixed to the top portions of the truncated cone-shaped main magnet members 12 and 16. The magnet unit 11 is formed into vertical symmetry with respect to a surface perpendicularly crossing the axis of the center hole 17 as a reference surface at an air gap center formed by the pole piece. When the diameter of the inscribing circle contacting to the outside peripheral surface of the main magnet member is D1, and the diameter of the inscribing circle contacting to the inside surface of the main magnet member is D2, D1/D2is not less than 2. COPYRIGHT: (C)2006,JPO&NCIPI