Patent ID: 6777938
Filing Date: 2004-08-17
Classification: G01R

Abstract:
A method for operating an NMR (nuclear magnetic resonance) magnet coil system having superconducting conductor structures with an overall magnetic inductance L0 for generating a homogeneous magnetic field B0 in a measuring volume, the method comprising the steps of:a) short-circuiting the magnet coil system using at least one superconducting switch (S0) through which an operating current I0 flows in a persistent mode; b) defining one or more disjoint partial regions (1, 2, . . . , nâˆ’1) of the magnet coil system which can be separately superconductingly short-circuited using one or more further superconducting switches (S1, S2, . . . , Snâˆ’1), each of said further switches provided between two points (P1, Q1), (P2, Q2), . . . (Pnâˆ’1, Qnâˆ’1) of a winding of the magnet coil system, said disjoint partial regions (1, 2, . . . , nâˆ’1) having associated inductances L1, L2, . . . , Lnâˆ’1 and generating magnetic field contributions B1, B2, . . . , Bnâˆ’1 to the homogeneous magnetic field B0 in the measuring volume, wherein Î±=&LeftBracketingBar;L0&it;&Sum;j=1n&it;(L-1)jn&it;BjB0&RightBracketingBar;&leq;0.8with 1&lE;j&lE;n and Bn being a magnetic field contribution to the homogeneous magnetic field B0 of a residual region (n) of the magnet coil system, reduced by said separately superconductingly short-circuited partial regions (1, 2, . . . , nâˆ’1), and having an inductance Ln, wherein (Lâˆ’1)jn is an entry of a jth line and nth column of an inverse of an inductance matrix of the magnet coil system, wherein L0 is said overall magnetic inductance equal to a sum of all entries of said inductance matrix; andc) activating said one or more further superconducting switches (S1, S2, . . . , Snâˆ’1) to separately superconductingly short-circuit said partial regions (1, 2, . . . , nâˆ’1) at a start of said persistent mode of the magnet coil system.