JPS6450349A - Superconductive lens for charged particle beam - Google Patents

Abstract

PURPOSE:To efficiently concentrate a magnetic flux to a lens action area to make a strong enough magnetic flux leak on a lens optical axis by inserting a superconductor in a pole piece gap of a normal conductive lens of a conventional type or by arranging a superconductive projection near a small gap of a superconductive diamagnetic shield member of a superconductive lens of a conventional type. CONSTITUTION:When a superconductive lens is constituted by inserting a superconductor 31 in a gap of a pole piece 30 of a normal conductive lens of a conventional type, magnetic flux leaking in the pole piece gap can be concentrated by the superconductor to a lens action area to make an efficient use of the magnetic flux. Since a magnetic yoke 32 and the pole piece 30 are made of a substance of a high magnetic permeability such as ferromagnetic, a high magnetic flux density is obtained with a relatively weak excitation. Also, if a superconductive lens is constituted by inserting a superconductive projection 63 in a small gap 62 of a superconductive diamagnetic shield member 61 of the superconductive lens, the magnetic flux 65 excited by a superconductive exciter coil 64 is locally bent by a perfect diamagnetic effect of the superconductive projection 63 and efficiently leaks through the small gap 62 onto the optical axis of the lens.