MAGNET IN WHICH TRAPEZOID SHIM IS PROVIDED IN POLE FACE

摘要

PROBLEM TO BE SOLVED: To suppress unevenness in the three-dimensional field of a magnet comprising first and second pole pieces having substantially opposing first and second pole faces arranged through an interval. SOLUTION: A first pole face 16 has an axis 42 extending substantially toward a second pole face 18 and a substantially circular shim tray 68 is fixed to the first pole face while being arranged to be substantially coaxial with the axis. The circular shim tray is provided with a substantially trapezoidal shim 70 when it is viewed oppositely to the first pole face. The trapezoidal shim can be arranged on an imaginary concentric circle on the circular shim tray where the trapezoids on the same circle have substantially the same shape and the trapezoids on different circle have different shapes.