# US 10,121,955 B2 · Superconducting magnet, MRI, and NMR

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- Number: US 10,121,955 B2
- Document ID: US10121955B2
- Status: Granted
- Kind: B2
- Application number: 15/100,702
- Filed: 2013-12-20
- Published: 2016-10-20
- Granted: 2018-11-06
- Earliest claimed: 2013-12-20
- Assignees: Hitachi, Ltd.
- Applicants: Hitachi, Ltd.
- Inventors: Hideki Tanaka; Tsuyoshi Wakuda
- Web page: https://patentgrep.com/patent/US10121955B2

## CPC

- H10N 60/84: Switching means for devices switchable between superconducting and normal states
- G01R 33/3815: with superconducting coils, e.g. power supply therefor
- H01F 6/008: {Electric circuit arrangements for energising superconductive electromagnets}
- H02H 1/0007: {concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445)}
- H02H 7/001: {for superconducting apparatus, e.g. coils, lines, machines}
- H10N 60/355: Power cryotrons
- H10N 60/80: Constructional details
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H)

## Abstract

An object of the present invention is to provide a persistent current switch with high heating efficiency by simplifying the configuration of the persistent current switch and reducing the heat capacity. To achieve the object, a superconducting magnet in accordance with the present invention includes a superconducting coil, a persistent current switch, and one of an alternating-current power supply, a pulsed power supply, or a charge/discharge circuit. The one of the alternating-current power supply, the pulsed power supply, or the charge/discharge circuit is connected to a loop circuit of the superconducting coil and the persistent current switch such that it is in parallel with the persistent current switch.

## Claims

### Claim 1

A superconducting magnet comprising:
a superconducting coil;
a persistent current switch; and
an alternating-current power supply, wherein
the alternating-current power supply is connected to a loop circuit of the superconducting coil and the persistent current switch such that the alternating-current power supply is in parallel with the persistent current switch,
the persistent current switch includes a superconducting wire,
the superconducting wire has disposed on an inner periphery thereof a normal conducting portion and a superconducting filament, and has disposed on an outer periphery thereof a sheath, and
provided that a frequency of the alternating-current power supply is f, a thickness of the sheath is t, a resistivity of a material of the sheath is ρ, and a permeability of the sheath is μ, t/2<√(ρ/πfμ).

### Claim 2 (depends on 1)

The superconducting magnet according to claim 1, wherein an alternating current flows through the outer periphery of the superconducting wire in a concentrated manner.

### Claim 3 (depends on 2)

The superconducting magnet according to claim 2, wherein a current passes through the sheath on the outer periphery of the superconducting wire in a concentrated manner, so that a Joule heat is generated and the superconducting wire is heated.

### Claim 4 (depends on 1)

The superconducting magnet according to claim 1, further comprising a protection circuit, the protection circuit being connected in parallel with the loop circuit of the superconducting coil and the persistent current switch.

### Claim 5 (depends on 4)

The superconducting magnet according to claim 4, wherein inductance of the protection circuit is higher than inductance of the persistent current switch.

### Claim 6 (depends on 1)

The superconducting magnet according to claim 1, further comprising a quench detector, the quench detector being connected in parallel with the loop circuit of the superconducting coil and the persistent current switch.

### Claim 7

A superconducting magnet comprising:
a superconducting coil;
a persistent current switch; and
one of a pulsed power supply or a charge/discharge circuit, wherein
the one of the pulsed power supply or the charge/discharge circuit is connected to a loop circuit of the superconducting coil and the persistent current switch such that the one of the pulsed power supply or the charge/discharge circuit is in parallel with the persistent current switch,
the persistent current switch includes a superconducting wire,
the superconducting wire has disposed on an inner periphery thereof a normal conducting portion and a superconducting filament, and has disposed on an outer periphery thereof a sheath, and
provided that a fundamental frequency of a waveform of a current supplied by one of the pulsed power supply or the charge/discharge circuit when expanded in a Fourier Series is f, a thickness of the sheath is t, a resistivity of a material of the sheath is ρ, and a permeability of the sheath is μ, t/2√(ρ/πfμ).

### Claim 8 (depends on 7)

The superconducting magnet according to claim 7, wherein a current from the one of the pulsed power supply or the charge/discharge circuit flows through the outer periphery of the superconducting wire in a concentrated manner.

### Claim 9 (depends on 8)

The superconducting magnet according to claim 8, wherein a current passes through the sheath on the outer periphery of the superconducting wire in a concentrated manner, so that a Joule heat is generated and the superconducting wire is heated.

### Claim 10 (depends on 1)

A Magnetic Resonance Imaging (MRI) or a Nuclear Magnetic Resonance (NMR) comprising the superconducting magnet according to claim 1.