Patent ID: 7928730

Claim:
Electromagnet apparatuses configured to generate a homogeneous magnetic field in a homogeneous magnetic field region having a pair of cryogenic vessels between which the homogeneous magnetic field region is interposed, the pair of cryogenic vessels lying along and intersecting a central axis passing through the homogeneous magnetic field region; each of the pair of cryogenic vessels including a superconducting main coil placed opposite each other and a superconductive shielding coil placed opposite each other, between which the homogeneous magnetic field region is interposed, and for passing a current in a direction reverse to a current of the superconductive main coil; each of the pair of cryogenic vessels having a first side nearest to the homogenous magnetic field region and a second side opposite the first side; a pair of first ferromagnetic members, each comprising one or more ferromagnetic materials, placed opposite each other along the central axis and within the pair of cryogenic vessels, each of the pair of first ferromagnetic materials having first sides closest to the first sides of the cryogenic vessels and having second sides opposite the first sides, wherein an outer periphery of the pair of first ferromagnetic members is a circle; a pair of second ferromagnetic members, each comprising one or more ferromagnetic materials, configured opposite each other along the central axis and within the pair of cryogenic vessels, and adjacent to the second side of each of the first ferromagnetic members relative to the homogeneous magnetic field region, respectively, wherein an outer periphery of the pair of second ferromagnetic members is a circle of which a diameter is larger than a diameter of the circle of the first ferromagnetic members.