Mitsubishi Denki Kabushiki Kaisha

Mitsubishi Denki K.k.

Moriaki Takechi

Shigenori Kuroda

Tatsuya Oue

Takahiro Matsumoto

Tsugio Watanabe

Toshiki Idemaru

Yuji Simada

Yosio Saitou

Takeshi Kataoka

A superconducting magnet apparatus has two or more divided superconducting coils successively arrayed in series and a magnetic shield. The divided superconducting coils arrayed in the axial direction are successively electrically connected in series, and protective diodes are connected between two connection points symmetrically-located with respect to the center of the serially-connected superconducting coil array as a reference.

Superconducting magnet apparatus with a magnetic shield

A magnetic field correction device for enhancing the homogeneity of a magnetic field generated by a magnet of a magnetic resonance imaging device. The correction device includes a plurality of magnetic shim holders disposed at predetermined circumferential angles on a support cylinder coaxial with the magnet. Each shim holder accommodates a magnetic shim element consisting of a first and a second magnetic bar member of distinct lengths and a first and a second non-magnetic tube for accommodating the first and second magnetic bar members therein. The members are positioned by respective stoppers inserted into the tubes.

Magnetic field correction device

A superconducting magnet apparatus comprising a superconducting main coil (1) for generating a uniform magnetic field and at least one superconducting shim coil (2a, 2b) electromagnetically coupled to the superconducting main coil (1) for increasing the uniformity of the magnetic field generated by the main coil (1). An emergency run down main coil heater element (21) is disposed adjacent to the main coil (1) for demagnetizing the latter, an emergency run down shim coil heater element (22a, 22b) is disposed in proximity of the shim coil (22a, 22b) for demagnetizing the latter, and a heater power source (24) is provided for supplying an electrical power to the heater elements (21,22a,22b). A switching unit (25,26,27) is connected between the heater elements (21,22a, 22b) and the heater power source (24) for connecting the heater power source (24) to the shim coil heater element (22a, 22b) and to the main coil heater element ( 21) at different time points with a predetermined time interval therebetween. The predetermined time interval may be selected such that the superconducting main coil (1) revert to a normal state after the superconducting shim coil (2a, 2b) has reverted to a normal state. The switching unit may include a first switch for selectively energizing the main coil heater element (21) and a second switch for selectively energizing the shim coil heater elements (22a, 22b) and a control unit for actuating the first and second switches at the different time points.

Superconducting magnet apparatus with an emergency run-down system

A superconducting magnet device includes a superconducting coil for generating a magnetostatic field, and a pulsating magentic field generating coil disposed on the inner diameter side of the superconducting coil. An inner cylinder of a thermal shielding tank located between the superconducting coil and the pulating magentic field generating coil is maintained at a temperature equal to or lower than the liquid nitrogen temperature. The inner cylinder is made of a superconductor which becomes superconductive at a temperature equal to or higher than the liquid nitrogen temperature. Further, a heating wire for heating the inner cylinder which is in a superconductive state to cause it to become normal conductive is provided on the inner cylinder of the thermal shielding tank in a direction in which it cuts across an induced current loop generated by the excitation of the static magnetic field.

Superconducting magnet device

A magnetic field compensating apparatus having a plurality of compensating units comprising a plurality of serial coils each of which is disposed concentrically along the main magnetic field and symmetrically with regard to a plane perpendicular to the main magnetic field and a plurality of power sources which separately supply currents to these compensating units, and made in such a manner that a plurality of error magnetic field components are generated by each of the compensating units, a compensating magnetic field is obtained by the whole of a plurality of the compensating units, and each of the currents supplied to the compensating units is decided in accordance with a constitution of a corresponding compensating unit.

Magnetic field compensating apparatus

A superconducting electromagnet apparatus wherein a superconducting main coil and a superconducting shield coil for reducing external magnetic field leakage generated by the main coil are magnetically, but not electrically, coupled, a single magnetizing power source is connected across the main coil, and persistent currect switches are respectively connected in parallel with the main coil and the shield coil.

Superconducting electromagnet apparatus

A nuclear magnetic resonance imaging apparatus has a superconducting coil which generates a static magnetic field, an electrically-conducting tubular heat shield which surrounds the superconducting coil, and a pair of confronting circular coils which are coaxial with the longitudinal axis of the cylindrical thermal shield and generate a gradient field in the longitudinal direction of the heat shield. The magnetic field generated by the circular coils induces eddy currents in the heat shield, and the eddy currents generate magnetic fields which form a composite magnetic field together with the magnetic field generated by the circular coils. The circular coils are positioned such that the terms in the expression for the magnetic flux density of the composite magnetic field which are proportional to the cube of the distance in the longitudinal direction of thermal shield cancel one another.

Nuclear magnetic resonance imaging apparatus

A superconducting electromagnet apparatus wherein a superconducting main coil and a superconducting shield coil for reducing external magnetic field leakage from the main coil are connected in series, a magnetizing power source is connected across the series connection assembly, and persistent current switches are respectively connected in parallel with the main coil and the shield coil.

A superconducting electromagnet for nuclear magnetic resonance imaging has a pair of Z gradient coils surrounded by a heat shield. The heat shield comprises an electrically-conducting tube having one or more cylindrical portions which have longitudinal slits formed therein and at least two annular portions which do not have slits and which are integral with the cylindrical portions. The annular portions are inductively coupled with the Z gradient coils. The axial positions of the centers of the annular portions are selected such that the sum of the cubic term in the expression for the magnetic field generated by eddy currents which are induced in the annular portions and the cubic term in the expression for the magnetic field generated by the Z gradient coils is equal to zero. The resulting composite magnetic field varies substantially linearly along the longitudinal axis of the electromagnet.

Superconducting electromagnet for NMR imaging

A superconducting magnet apparatus comprises a superconducting coil, a persistent current switch with a small current bearing capacity, and a protective element respectively connected in parallel with the superconducting coil and an emergency run down unit including a heater circuit having a heater power source, a heater element disposed in proximity to the superconducting coil, and a heater circuit switch connected in series with the heater element. Thus, the heater element is energized and warmed to bring at least a part of the superconducting coil into a normal state.

Superconducting magnet apparatus with emergency run down unit

An electromagnet has a magnetic shield whose end plate is formed with an asymmetrical side hole 10 in addition to a center opening 6. The thickness of portion 11 of the end plate which covers an area defined by a deviation angle of not more than 180.degree. with a center line passing through a center of the side hole is made larger than the remaining portion of the end plate.

Electromagnet having magnetic shield

A superconducting magnet apparatus comprises an emergency run down unit having a heater power source and a heater circuit switch, a superconducting coil, and a persistent current switch circuit, the persistent current switch connected in parallel to the superconducting coil and including a first persistent current switch connected in parallel to a first protective element of low resistance and a second persistent current switch connected in parallel to a second protective element of high resistance. The second persistent current switch has a persistent switch-heater connected to the heater power source through the heater circuit switch. Thus, when it becomes necessary to demagnetize the superconducting magnet apparatus being operated in a persistent current mode, the second persistent current switch parallel to the second protective element of high resistance is opened, whereby current flowing through the superconducting magnet decays rapidly.

A superconducting magnet comprising a superconducting coil for generating a magnetic field when current flows therethrough and a vacuum heat insulation vessel storing and maintaining therein the coil at a cryogenic temperature, said vacuum heat insulation vessel having a part, such as a cylindrical outer wall, made of a ferromagnetic material which provides a path of high magnetic permeability for outwardly-directed flux lines of the magnetic field generated by said coil to reduce the spread of the flux lines and weaken the magnetic field outside the vessel.

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Ako, Japan

Moriaki Takechi