Abstract: A method of shimming a magnet having correction coils is provided. The field strength in the bore of the magnet is measured at a predetermined number of points. The field inhomogeneity is determined from the measured field strengths. The field created by a fixed current in each shim coil operating alone, at each of the predetermined points is determined. The shim correction coil currents are determined using a linear programming solver to minimize the field inhomogeneity and the correction coil currents. The correction coil currents are determined based on the measured field in the bore of the magnet and the field created by each of the shim coils when carrying a fixed current, with the correction coil currents each constrained to a maximum value which is adjusted for the current in the correction coils when the field strength was measured. The correction coils are adjusted to the determined values and the fields strength of the magnet is gain measured at the predetermined points.

Abstract: A passive shim assembly for a magnet having a central bore is provided. The passive shim assembly includes a plurality of axially extending guide rails bonded directly to the bore of the magnet and equally spaced circumferentially. A plurality of arcuately shaped drawers are slidably mounted between adjacent channel pieces. A plurality of stacks of arcuate strips of magnetic flux conducting material demountably secured to each of the drawers, the strips extending in the circumferential direction.

Abstract: An apparatus for installing shim guide rails in an MR magnet is provided including a plurality of beam members, one for every guide rail to be installed. A plurality of coaxial ring shaped members spaced apart from one another are joined together by the beam members. The beam members extend axially and are spaced circumferentially about the outer diameter of the ring shaped members forming a cylindrical open ended cage. Each of the beam members defines a plurality of radially extending spaced apart apertures. A plurality of ladder-like structures each of which is associated with a respective beam member is provided. Each of the ladder-like structures included two side pieces joined by a plurality of rungs extending between the side pieces. The rungs pass through the holes in the beam members with one of the side pieces situated inside the cylindrical cage and the other situated outside the cage.

Abstract: A superconducting switch is bifilarly wound with two superconductors. The superconductors are wound around a core inside a housing and are electrically insulated from one another. One of the superconductors is radially further out than the other and a common heater element is between the superconductors to switch both superconductors substantially simultaneously between the persistent and non-persistent states.