Patent ID: 6781494
Filing Date: 2004-08-24
Classification: G01R

Abstract:
A magnet system for generating a magnetic field (H) in a direction of a z axis in a working volume (AV) disposed on the z axis about z=0, wherein the magnetic field (H) of the magnet system can be expanded along the z axis about z=0 in a polynomial in z having coefficients Hn, the system comprising:a radially inner partial coil system (C1); a radially outer partial coil system (C2) disposed coaxially with respect to said radially inner system, said inner and outer coil system having magnetic dipole moments in an operating state of opposite signs and differing by an amount &Dgr;m with |&Dgr;m|<2.5% of a magnitude of a magnetic dipole moment of said radially inner partial coil system, said inner and said outer coil system being parts of an actively shielded superconducting magnet coil system (M); an external device for current supply; and at least one current path (P1, . . . , Pn) which is superconductingly closed in an operating state, said current paths (P1, . . . , Pn) each being charged, in an operating state, by said external current supply device with a respective current (IP1, . . . IPn), wherein said current paths (P1, . . . Pn) have an overall contribution to the magnetic field (H) of the magnet system in the operating state in the working volume (AV) of the magnet system of an amount which is less than 5% of a field contribution of said magnet coil system (M) in the operating state, wherein, when optimizing a fringe field behavior outside of the magnet system, an overall magnitude of magnetic dipole moments of said current paths (P1, . . . , Pn) charged to their respective operating currents (IP1, . . . , IPn) is at least 0.1% of a magnitude of a magnetic dipole moment of a charged said outer partial coil system (C2), wherein, when charging said current paths (P1, . . . , Pn) to their respective operating current (IP1, . . . , IPn), a resulting change &Dgr;H2 of a coefficient of second order (H2) of the polynomial expansion of the magnetic field (H) of the magnet system is given by: |&Dgr;H2|T/m2, 0.9Â·|H2(M)|), wherein H2(M) designates the coefficient of second order of the polynomial expansion of the magnetic field of said actively shielded superconducting magnet coil system (M) in the operating state.