Magnetically shielding structure

A magnetically shielding structure comprising:

• a cylindrical shielding body extending along an axis disposed in a longitudinal direction and composed of a superconductive material which manifests a Meissner effect after transition from a normal conductive state to a superconductive state when said cylindrical shielding body is cooled below a predetermined critical temperature,
• cylindrical collar means, made of a highly permeable material and having an outer diameter smaller than an inner diameter of said cylindrical shielding body and a through opening oriented in the longitudinal direction along which said axis extends, for absorbing and magnetically shorting a penetrating magnetic field, said cylindrical collar means being disposed outside and in the vicinity of an opening end of said cylindrical shielding body,
• said cylindrical collar means comprising a plurality of highly permeable collars arranged coaxially in a multiple layer construction to form a space between each of said collars, and
• cylindrical shielding cover means, made of a highly permeable material and having an inner diameter larger than the outer diameter of said cylindrical shielding body, for coaxially covering over the outer circumference of said cylindrical collar means and of said cylindrical shielding body, said cylindrical shielding cover means being displaced relative to said cylindrical shielding body so that a space between said cylindrical shielding cover means and said cylindrical shielding body is provided.