Patent ID: 6496091
Filing Date: 2002-12-17
Classification: G01R,H01F

Abstract:
A superconducting magnet device (M, S, P1, . . . , Pn) for generating a magnetic field in a direction of a z axis in a working volume disposed about z=0, and the device comprising:a magnet coil system (M) with at least one current-carrying superconducting magnet coil; at least one additional superconductingly closed current path (P1, . . . , Pn), wherein magnetic fields generated in the z direction in the working volume by said addition al current paths (P1, . . . , Pn) due to induced currents do not exceed a magnitude of 0.1 Tesla; a shim device (S) with at least one superconducting shim coil, said shim device (S) generating a field which varies along the z axis with a kth power of z for an even power of k>0, said shim device (S) designed such that a variable gSeff=gSâˆ’gTÂ·(Lclâˆ’&agr;Lcor)âˆ’1Â·(Lâ† Sclâˆ’&agr;Lâ† Scor) is substantially zero and an absolute value ofgSeff,cl=gSâˆ’gTÂ·(Lcl)âˆ’1Â·Lâ† Scl is larger than zero, wherein said variables have following definitions:âˆ’&agr;: average magnetic susceptibility in a volume of said magnet coil system (M) with respect to field fluctuations which do not exceed a magnitude of 0.1 T, wherein 0gT=(gM, gP1, . . . , gPj, . . . , gPn), gPj: Field per ampere of said current path Pj in the working volume without field contributions of said current paths Pi for iâ‰ j, of said magnet coil system (M), and of said shim device (S), gM: Field per ampere of said magnet coil system (M) in the working volume without field contributions of said current paths (P1, . . . , Pn) and without field contributions of said shim device (S), gS: Field per ampere of said shim device (S) in the working volume without field contributions of said current paths (P1, . . . , Pn) and without field contributions of said magnet coil system (M), Lcl: Matrix of inductive couplings between said magnet coil system (M) and said current paths (P1, . . . , Pn) and among said current paths (P1, . . . , Pn), Lcor: Correction for said inductance matrix Lcl, which would result with complete diamagnetic expulsion of disturbance fields from said volume of said magnet coil system (M), Lâ† Scl: Vector of inductive couplings of said shim device (S) with said magnet coil system (M) and said current paths (P1, . . . , Pn), Lâ† Scor: Correction for said coupling vector Lâ† Scl, which would result with complete diamagnetic expulsion of disturbance fields from said volume of said magnet coil system (M).