WO2024048179A1 - Dispositif à aimant supraconducteur et dispositif de diagnostic par résonance magnétique nucléaire - Google Patents

Dispositif à aimant supraconducteur et dispositif de diagnostic par résonance magnétique nucléaire Download PDF

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WO2024048179A1
WO2024048179A1 PCT/JP2023/028156 JP2023028156W WO2024048179A1 WO 2024048179 A1 WO2024048179 A1 WO 2024048179A1 JP 2023028156 W JP2023028156 W JP 2023028156W WO 2024048179 A1 WO2024048179 A1 WO 2024048179A1
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superconducting
current
magnet device
coil
temperature
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English (en)
Japanese (ja)
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毅 和久田
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株式会社日立製作所
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H01F6/04—Cooling

Definitions

  • the present invention relates to a superconducting magnet device that generates a high magnetic field and utilizes the magnetic field, and a nuclear magnetic resonance diagnostic device.
  • a superconducting magnet device can generate a higher magnetic field than permanent magnets or normal conducting electromagnets. For this reason, superconducting magnet devices are widely used as ultra-high magnetic field magnets for research, magnets for analysis devices such as NMR (nuclear magnetic resonance), and magnets for medical MRI (Magnetic Resonance Imaging). .
  • the operating modes of superconducting magnet devices are broadly classified into two (see, for example, Patent Document 1).
  • the first operation mode is a power drive mode in which a magnetic field is generated by supplying current from the power supply to excite the magnet, and the current continues to flow from the power supply during operation.
  • a superconducting circuit is constructed by installing a persistent current switch (PCS) in the superconducting magnet, a current is applied to the superconducting circuit from the power source to generate a magnetic field, and then the current is supplied from the power source.
  • PCS persistent current switch
  • persistent current mode which operates while disconnected from the power supply, there is no noise intrusion from the power supply, so a temporally stable magnetic field can be obtained.
  • applications such as NMR and MRI that utilize this property and particularly require stability of the magnetic field, conventional wisdom has believed that operation in persistent current mode is essential.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a superconducting magnet device and a nuclear magnetic resonance diagnostic device that can realize a temporally stable magnetic field in drive mode operation.
  • a superconducting magnet device is a superconducting magnet device comprising a superconducting coil around which a superconducting wire is wound, and a power source for exciting the superconducting coil, A switch element and a protective resistor are connected in parallel to the coil, and the switch element is made of a high-temperature superconductor wire, and the current capacity of the switch element is greater than the rated operating current of the superconducting coil.
  • the switching element is sufficiently small and electrically shorts the superconducting coil in a low resistance state when a predetermined magnetic field is being generated, and in a high resistance state when the magnetic field is changing.
  • the main feature is that the superconducting coil operates to spontaneously change its open/close state by changing the amount of current supplied from the power source to the superconducting coil.
  • a temporally stable magnetic field can be realized in drive mode.
  • FIG. 1 is a circuit diagram showing the basic configuration of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 2 is a circuit diagram showing the basic configuration of a superconducting magnet device according to a comparative example. 1 is a conceptual diagram showing a basic mounting state of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 2 is an equivalent circuit diagram for explaining magnetic field stabilization realized by the superconducting magnet device according to the embodiment of the present invention.
  • FIG. 3 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil during the excitation process of the superconducting magnet device according to the embodiment of the present invention.
  • FIG. 2 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil during a demagnetization process of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 4 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil in a current adjustment process of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 6 is a diagram showing temporal changes in currents flowing through each of the excitation power source and the superconducting coil when the superconducting magnet device according to the embodiment of the present invention is subjected to pre-energization operation.
  • FIG. 4 is a diagram showing temporal changes in currents flowing through each of an excitation power source and a superconducting coil in a current adjustment process of a superconducting magnet device according to an embodiment of the present invention.
  • FIG. 6 is a diagram showing temporal changes in currents flowing through each of the ex
  • FIG. 1 is a conceptual diagram showing a first mounting state of a superconducting magnet device according to an embodiment of the present invention. It is a conceptual diagram showing an example of operating temperature setting concerning a superconducting bypass element. It is a conceptual diagram showing an example of operating temperature setting concerning a superconducting bypass element. It is a conceptual diagram showing the 2nd mounting state of the superconducting magnet device concerning an embodiment of the present invention. It is a conceptual diagram showing the 3rd mounting state of the superconducting magnet device concerning an embodiment of the present invention.
  • FIG. 1 is an explanatory diagram showing a nuclear magnetic resonance diagnostic apparatus using a superconducting magnet device according to an embodiment of the present invention.
  • HTS high temperature superconductors
  • REBCO rare earth elements
  • BSCCO rare earth elements
  • MgB 2 magnesium diboride
  • the high-temperature superconductor HTS has a high critical temperature, and by utilizing this property, it is operated in a temperature range where the specific heat is an order of magnitude higher than that of liquid helium. Therefore, high-temperature superconducting magnets (HTS magnets) can be put to practical use in that they have an order of magnitude larger quench energy margin than LTS magnets against the normal conduction transition phenomenon (quench) caused by thermal energy input into the superconducting magnets due to disturbances. It is expected that
  • a superconducting coil means a coil (winding) using a superconductor as a wire.
  • a superconducting coil and a superconducting magnet (sometimes simply called a “magnet” or “magnet”) have substantially the same meaning.
  • a superconducting coil is sometimes simply abbreviated as a "coil.”
  • a superconducting magnet (superconducting coil)
  • the energy stored in the coil is used to prevent the coil from burning out. must be promptly recovered from the coil.
  • the superconducting magnet operated in the drive mode is equipped with a protective resistor (see numeral 25 shown in FIGS. 1 and 2) that converts this energy into heat and recovers it.
  • superconducting magnets that use the low-temperature superconductor LTS as a wire
  • the superconducting coils actively or passively enter a resistance state, and part of the stored energy is used to increase the temperature of the coils. It will bring.
  • the quench margin is small, so when quench buds occur, the resistance region quickly expands, and the stored energy is converted into heat due to the electrical resistance. That is, in the chamber of the cryostat (see reference numeral 18 shown in FIGS. 1 and 2), a shunt resistor/diode is provided in parallel with the superconducting coil. The energy stored in the superconducting coil is distributed and recovered between the electrical resistance inside the coil and these shunt resistors or diodes. Furthermore, in a coil that has a large amount of stored energy, the resistance area is actively expanded using a heater or the like to recover energy in a wide resistance area and prevent burnout of the coil.
  • HTS magnets have a large quench margin, so even if quench occurs, the expansion speed of the resistance region is about two orders of magnitude slower than that of LTS magnets, and resistance generation is limited to a small region. Therefore, the energy stored in the coil is consumed in this small area, which may easily lead to burnout.
  • HTS magnets it is also possible to expand the resistance range using a heater, just as with LTS magnets.
  • HTS magnets have a problem in that they require more thermal energy input than LTS magnets.
  • energy recovery during quenching of the HTS magnet mainly involves external energy recovery, and requires an energy recovery mechanism by turning off the persistent current switch PCS at high speed and by shutting off the power.
  • the persistent current switch PCS is also made of the high temperature superconductor HTS.
  • the persistent current switch PCS (see reference numeral 53 in the comparative example shown in FIG. 2) is generally equipped with a heater (see reference numeral 57 in the comparative example shown in FIG. 2).
  • the persistent current switch PCS itself is put into a resistance state (switched off) by heating it with a heater.
  • a large amount of thermal energy is required to bring the persistent current switch PCS made of the high-temperature superconductor HTS into a resistance state.
  • the present invention provides an excitation power source 23 (referred to as "current source I") for exciting a superconducting coil 11 made of a high-temperature superconductor HTS as a wire, as shown in FIG. ), to which the superconducting coil 11 is connected, and at both ends of the superconducting coil 11, there is a superconducting bypass made of a high-temperature superconductor HTS, which exhibits a sufficiently smaller current capacity than the rated operating current of the superconducting coil 11, as a wire.
  • An embodiment of a superconducting magnet device 10 configured by superconductingly connecting elements 15 will be disclosed. According to the superconducting magnet device 10 according to the present invention, by operating the device 10 in the drive mode, a temporally stable magnetic field can be obtained at low cost while protecting the magnet during quenching.
  • FIG. 1 is a circuit diagram showing the basic configuration of a superconducting magnet device 10 according to an embodiment of the present invention.
  • conductive wires and the like containing a superconductor as a wire are illustrated with thick solid lines
  • conductive wires and the like containing a normal conductor as a wire are illustrated with thin solid lines.
  • a "superconductor” is a substance whose electrical resistance becomes substantially zero below the superconducting critical temperature (which causes a superconducting phenomenon).
  • a superconducting magnet device 10 connects a superconducting bypass element (a "switch element") to a superconducting coil 11 via a first conducting wire 13 made of a superconductor (preferably a high-temperature superconductor HTS). ) 15 connected to the superconducting circuit 16; ) 23 and a protective resistor 25.
  • a superconducting bypass element a "switch element”
  • HTS high-temperature superconductor
  • a magnetic field is generated in the superconducting coil 11 by receiving current from the excitation power source 23 connected in series via the first conducting wire 13 and the power lead 17.
  • the superconducting coil 11 is a coil made of a high-temperature superconductor HTS as a wire material.
  • the high temperature superconductor HTS used in the superconducting coil 11 is not particularly limited, but for example, magnesium diboride (MgB 2 ) can be used.
  • MgB 2 magnesium diboride
  • the superconducting coil 11 is connected in series to an excitation power source 23 via a first conducting wire 13 and a pair of power leads 17a, 17b, etc., respectively.
  • the pair of power leads 17a and 17b may be collectively referred to as "power leads 17."
  • a superconducting bypass element 15 is connected to both ends of the superconducting coil 11 via a first conducting wire 13 in a superconducting manner or with a sufficiently low resistance.
  • “superconductingly connected” means, in addition to pressure welding or spot welding, connecting superconductors to each other via superconducting solder or a superconducting phase.
  • the superconducting bypass element 15 is made of a high-temperature superconductor HTS having a sufficiently small (1% or less) current capacity with respect to the rated operating current of the superconducting coil 11.
  • the high temperature superconductor HTS used in the superconducting bypass element 15 is not particularly limited, but for example, magnesium diboride (MgB 2 ) can be suitably employed.
  • the superconducting bypass element 15 suppresses current inflow into the superconducting coil 11 by bypassing a fluctuating current (noise current) that is smaller than the current capacity of the element 15 with respect to the fluctuating component of the current supplied from the excitation power source 23. On the other hand, it has a function of flowing a current exceeding the current capacity to the superconducting coil 11.
  • the superconducting coil 11 short-circuited by the superconducting bypass element 15 does not operate the persistent current switch PCS (see reference numeral 53 in the comparative example shown in FIG. 2 described later) normally used in persistent current mode operation. (without providing the heater 57 in the persistent current switch PCS53), excitation and demagnetization can be performed.
  • the superconducting magnet device 10 according to the embodiment of the present invention although the superconducting coil 11 behaves like a normal electromagnet, it is possible to achieve magnetic field stability equivalent to persistent current mode operation.
  • the superconducting first conducting wire 13 and the normally conducting power lead 17 are connected in a normal conducting manner by a joining means such as soldering.
  • the normally conductive power lead 17 and the normally conductive second conducting wire 19 are connected to each other by a joining means such as soldering.
  • a protective resistor 25 is connected in parallel to the superconducting circuit 16 including the superconducting coil 11 via the first conducting wire 13 and the power lead 17.
  • the protective resistor 25 plays the role of recovering the energy accumulated in the superconducting coil 11 during quenching.
  • the excitation power source 23 plays a role of supplying DC excitation current to the superconducting coil 11 via the second conductive wire 19, the power lead 17, and the first conductive wire 13, respectively.
  • the excitation current supplied by the excitation power supply 23 is variably set to an appropriate magnitude.
  • a pair of circuit breakers 21a and 21b are inserted and connected to both ends of the excitation power source 23 of the second conducting wire 19.
  • the pair of circuit breakers 21a and 21b serve to disconnect the excitation power source 23 from the superconducting circuit 16 including the superconducting coil 11 during quenching.
  • the superconducting bypass element 15 having a smaller current capacity than the rated operating current of the superconducting coil 11 is connected to both ends of the superconducting coil 11 in a superconducting manner, and the superconducting coil 11 is An excitation power source 23 for excitation is connected to the superconducting coil 11 for operation. That is, the superconducting bypass element 15 and the protective resistor 25 are connected to the superconducting coil 11 in parallel.
  • the superconducting bypass element 15 which is a switch element, is configured using a high-temperature superconductor HTS as a wire, and the current capacity of the superconducting bypass element 15 is sufficiently smaller than the rated operating current of the superconducting coil 11.
  • the superconducting bypass element 15 electrically short-circuits the superconducting coil 11 in a low resistance state (switch-on state) while generating a predetermined magnetic field. , when changing the magnetic field, it enters a high resistance state (switched off state), and changes the open/close state spontaneously (passively) by changing the amount of current supplied from the excitation power supply 23 to the superconducting coil 11. It works like this.
  • the open/close state of the superconducting bypass element 15 can be spontaneously (passively) changed by changing the amount of current supplied from the excitation power source 23 to the superconducting coil 11. Since the superconducting coil 11 is excited/demagnetized only by turning on/off current from the excitation power source 23, a temporally stable magnetic field can be realized in drive mode operation.
  • FIG. 2 is a circuit diagram showing the basic configuration of a superconducting magnet device 50 according to a comparative example.
  • conductive wires made of a superconductor are shown as thick solid lines
  • conductive wires made of a normal conductor are shown as thin solid lines.
  • the superconducting magnet device 10 according to the embodiment of the present invention and the superconducting magnet device 50 according to the comparative example have similar basic configurations. Therefore, the description will focus on the differences between the two, instead of the description of the basic configuration of the superconducting magnet device 50 according to the comparative example.
  • the superconducting circuit 52 is made of a superconductor (not the high-temperature superconductor HTS), as shown in FIG.
  • a persistent current switch PCS 53 is connected in parallel to the superconducting coil 51 via the first conducting wire 13.
  • the persistent current switch PCS 53 belonging to the superconducting circuit 52 includes a superconducting wire 55 made of a superconductor (not a high-temperature superconductor HTS) and a heater 57 for heating the superconducting wire 55. It consists of: Heater 57 is provided close to superconducting wire 55 . A heater power source 59 is connected to the heater 57 .
  • a superconducting circuit 52 provided in a superconducting magnet device 50 receives a current supply from an excitation power source 23 connected in series via a first conductive wire 13 and a power lead 17, and includes a superconducting coil 51 and a superconducting conductive wire 55. A predetermined persistent current is circulated within the superconducting circuit 52. Thereby, the superconducting circuit 52 generates a magnetic field in the superconducting coil 51.
  • the superconducting wire 55 when the superconducting wire 55 is heated by the heater 57 and the temperature of the superconducting wire 55 exceeds a predetermined superconducting critical temperature, the superconducting wire 55 changes from the superconducting state to the normal state. It transitions to a conductive state (that is, the persistent current switch PCS53 turns off). Thereafter, when the heating by the heater 57 is stopped and the superconducting wire 55 is cooled down to below the superconducting critical temperature, the superconducting wire 55 transitions to a superconducting state (that is, the persistent current switch PCS 53 is turned on).
  • FIG. 3 is a conceptual diagram showing the basic mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
  • the superconducting circuit 16 included in the superconducting magnet device 10 according to the embodiment of the present invention is housed in a cryostat 18, which is an insulated vacuum container.
  • the cryostat 18 is configured to cool the indoor temperature of the cryostat 18 to below a predetermined superconducting critical temperature using an electric refrigerator (see reference numeral 31 in FIG. 9), liquid helium, nitrogen, hydrogen, argon, etc. There is.
  • the cryostat 18 has a pair of through holes 20 for inserting the power lead 17 therethrough.
  • a pair of power leads 17 connected to the superconducting circuit 16 are fixed to the cryostat 18 while being inserted through the pair of through holes 20 .
  • the side of the power lead 17 connected to the excitation power source 23 is exposed to the outside of the cryostat 18 .
  • FIG. 4 is an equivalent circuit diagram for explaining the principle of magnetic field stabilization realized by the superconducting magnet device 10 according to the embodiment of the present invention.
  • the problem here is the DC component (drift). This can be considered as part of periodic noise that fluctuates with an extremely long time constant. Regarding this as well, the cutoff frequency fc may be appropriately set by considering that the period varies in a 24-hour period, for example. However, this concept requires a resistance R of extremely small value. Therefore, consider the DC component as follows. That is, in the equivalent circuit shown in FIG. 4, the time change I(t) of the current supplied from the current source I is considered as shown in (Equation 1).
  • I0 is the set current value
  • a is the amount of variation per unit time.
  • the relationship between the current IL flowing in the coil (superconducting coil 11) and the current IR flowing in the resistor (superconducting bypass element 15) can be described as (Equation 2).
  • the stability of the magnetic field is required to be 0.1 ppm in one hour of magnetic field use, and the inductance L of the superconducting coil 11 is 96H, then The resistance value that satisfies this requirement is 5.3 microohms or less.
  • the time constant ⁇ at this time is about 5000 hours, the cutoff frequency is 8.8 nHz, and the 10 Hz current noise is reduced by about 9 orders of magnitude. In this way, it has been found that by short-circuiting the superconducting coil 11 with a microohm-order resistance (superconducting bypass element 15), stabilization of the magnetic field can be achieved.
  • the superconducting bypass element 15 needs to be turned off when applying current to the coil (superconducting coil 11) or drawing current from the coil, but turned on when generating and using a constant magnetic field.
  • implementation can be considered in which the superconducting bypass element 15 is turned on and off by providing a heater 57 close to the superconducting bypass element 15, like the persistent current switch PCS53 (see FIG. 2) according to the comparative example.
  • PCS53 persistent current switch
  • a wire made of a high-temperature superconductor HTS having a sufficiently small critical current characteristic (for example, 1%) with respect to the rated operating current of the coil (superconducting coil 11) is used to conduct superconducting.
  • a sufficiently small critical current characteristic for example, 1%) with respect to the rated operating current of the coil (superconducting coil 11)
  • the superconducting bypass element 15 spontaneously (passively) performs superconducting without actively driving the heater 57 like the persistent current switch PCS53 according to the comparative example. By making the transition to normal conductivity, a switching operation related to on/off control can be realized.
  • FIG. 5 shows a schematic diagram of the time change in the supply current from the current source I and the time change in magnetic field generation (coil current) during the excitation process.
  • the solid line in FIG. 5 represents the time change in the current supplied from the current source I, and the broken line represents the time change in the generated magnetic field (coil current).
  • the current flowing through the superconducting bypass element 15 has not reached the critical current value, the element 15 maintains its superconducting state, and no current flows through the coil (superconducting coil 11) for a while. It does not flow (see the section from time t0 to time t51 shown in FIG. 5).
  • FIG. 6 shows a schematic diagram of the time change in the current supplied from the current source I and the time change in magnetic field generation (coil current) during the demagnetization process.
  • the solid line in FIG. 6 represents the time change of the supplied current from the current source I, and the broken line represents the time change of the generated magnetic field (coil current).
  • the supply current value of the current source I is gradually decreased linearly from the point where the current source I is operated at a constant value (see the section before time t61 shown in FIG. 6) (see the section after time t61 shown in FIG. 6). From the coil and the superconducting bypass element 15, it appears that a current in the opposite direction from the current source I is superimposed and swept, and the same phenomenon as in the excitation process occurs regarding this reverse direction current.
  • the current supply from the current source I can be performed without being conscious of turning on/off the heater 57 or adjusting the current. It becomes possible to excite and demagnetize the magnet (superconducting coil 11) only by manipulating the amount.
  • Sufficient energy (calorific value) is required to completely bring the superconducting bypass element 15 into a normal conducting state using Joule heat, and this is due to the normal conducting resistance of the high temperature superconductor HTS that constitutes the superconducting bypass element 15 and the superconducting bypass element. It is determined by Joule heat generation, which is determined by the square product of the current flowing through 15, and the heat generation duration time.
  • the current is suddenly increased to instantly increase the heat generation of the superconducting bypass element 15 (pre-energization operation:
  • the time delay can be shortened. Therefore, by designing and controlling the current sweep speed and current input amount in the pre-energization before the start of the current sweep, the time required to transition the superconducting bypass element 15 to the resistance state and the current input speed to the coil can be controlled. be able to.
  • the current capacity of the superconducting bypass element 15 is sufficient as long as it can pass the ripple noise current of the current source I, and if the current capacity is too large, a large current is required to bring the superconducting bypass element 15 into a voltage generating state. It becomes wasted. Therefore, the current capacity of the superconducting bypass element 15 is approximately less than 1% of the rated operating current of the superconducting coil 11, and the current is approximately less than 1 A.
  • the superconducting bypass element 15 When the superconducting bypass element 15 is in a resistance state (switch-off state), the accumulated energy of the superconducting coil 11 is distributed to the protective resistor 25 and the normal resistance (electrical resistance in the switch-off state) of the superconducting bypass element 15 in inverse proportion to each other. and recovered as heat.
  • the normal resistance of the superconducting bypass element 15 is not sufficiently large with respect to the protective resistor 25, the energy of the magnet is recovered inside the cryostat 18 in which the superconducting bypass element 15 is provided, so that recooling takes time. Further, a heat capacity is required to prevent the superconducting bypass element 15 itself from being burnt out.
  • the value of the electrical resistance of the superconducting bypass element 15 in the switch-off state is set to a value that is 10 times or more, preferably 30 times or more, as compared to the value of the electrical resistance of the protective resistor 25.
  • the superconducting bypass element 15 was designed so that the electrical resistance value in the switch-off state was 100-300 ohms.
  • the superconducting coil 11 was manufactured by winding 85 m of a magnesium diboride (MgB 2 ) superconducting single core wire with a wire diameter of 0.64 mm and having a base material of niobium titanium alloy (Nb-Ti).
  • the superconducting bypass element 15 was also manufactured using the magnesium diboride (MgB 2 ) superconducting single core wire.
  • the resistivity of this superconducting single core wire at 40K is designed to be 38 x 10 ⁇ -8 ohm meters, and the electrical resistance value at this time is 100 ohms.
  • the critical current value is defined as the current when an electric field of 1 ⁇ 10 ⁇ -4 [V/m] is generated.
  • the wire length of the superconducting coil 11 is 85 m
  • the voltage generated in the superconducting bypass element 15 when a current corresponding to the critical current value flows through the element 15 is 8.5 mV.
  • the superconducting coil 11 is excited by the voltage (8.5 mV) generated in the superconducting bypass element 15.
  • the inductance of the superconducting coil 11 is 96H, the rate of increase in the current applied to the superconducting coil 11 by this voltage is 89 ⁇ A/sec. Under these conditions, it would take as much as 780 hours to excite the magnet to the rated operating current (250 A), which is not realistic.
  • the current capacity of the superconducting bypass element 15 only needs to have a capacity for transmitting current noise, and as mentioned above, it is desirable to have a small current capacity from the viewpoint of voltage generation. Therefore, the current capacity of the superconducting bypass element 15 is approximately 1% or less (or 1 A or less) with respect to the rated operating current of the superconducting coil 11.
  • HTS copper oxide superconductor
  • BSCCO bismuth-based superconductor
  • MgB 2 magnesium diboride
  • the superconducting bypass element 15 is provided at a location that belongs to a temperature range higher than the rated operating temperature of the superconducting coil 11.
  • the temperature range related to this temperature region is set below the critical temperature of the superconducting bypass element 15 and within 5K with respect to the critical temperature. In this way, by providing the superconducting bypass element 15 at a location that belongs to a temperature range higher than the rated operating temperature of the superconducting coil 11 and operating the superconducting bypass element 15 near the critical temperature, the rated operating temperature of the superconducting coil 11 can be achieved.
  • a superconducting bypass element 15 having a current capacity on the order of 1% of current is realized.
  • the superconducting bypass element 15 by installing the superconducting bypass element 15 in a relatively high-temperature atmosphere environment, it can be transferred to the normal conductive state even with a slight Joule heat generation, so that the superconducting bypass element 15 can easily be placed in the resistance state (switched off state). ).
  • the inductance is often reduced to zero by using non-inductive winding, but in the embodiment according to the present invention, the superconducting bypass element 15 is inductively wound. By doing so, the current transport characteristics are reduced by the self-magnetic field generated in the superconducting bypass element 15 during excitation and demagnetization.
  • the ambient temperature at the location where the superconducting bypass element 15 is installed is set to be just below the critical temperature of the superconductor. Near the critical temperature, it becomes sensitive to magnetic fields, making it possible to more effectively reduce the current capacity. As a result, a superconducting bypass element 15 with good controllability can be realized.
  • the inductively wound superconducting bypass element 15 has an inductance, and the noise current is distributed between the superconducting coil 11 and the superconducting bypass element 15 with an inverse ratio of impedance between the superconducting coil 11 and the superconducting bypass element 15. become.
  • the inductance of the superconducting coil 11 is on the order of 100H, and by configuring the inductance of the superconducting bypass element 15 on the order of 1 mH, the incorporation of ripple noise can be reduced to approximately one hundred thousandth. Ripple noise is sufficiently small compared to 1 ⁇ 10 ⁇ -3.
  • the superconducting bypass element 15 is inductively wound on the order of 1 mH, the magnetic field fluctuation due to ripple noise can be suppressed to the order of 1 ⁇ 10 ⁇ -7, so that no practical problem occurs in MRI applications, for example.
  • FIG. 9 is a conceptual diagram showing a first mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
  • illustrations of the excitation power source 23, protection resistor 25, etc. connected to the power lead 17 are omitted (because they are similar to the example shown in FIG. 3).
  • the superconducting magnet device 10 employing this first mounting state is a conduction-cooled superconducting magnet device for tunnel-type MRI that generates a horizontal magnetic field.
  • the superconducting magnet device 10 is equipped with an electric refrigerator 31.
  • the electric refrigerator 31 for example, a Gifford-McMahon refrigerator (GM refrigerator), which is a two-stage refrigerator, can be employed.
  • GM refrigerator Gifford-McMahon refrigerator
  • This electric refrigerator (GM refrigerator) 31 has a two-stage cooling capacity, and the first stage (the first stage 33 related to the electric refrigerator 31) can cool down to 80K or less, and the second stage (Second stage 35 related to electric refrigerator 31) can cool to a range of about 4-10K.
  • the superconducting circuit 16 provided in the superconducting magnet device 10 is operated in a state where it is conductively cooled by the action of the electric refrigerator 31.
  • the superconducting coil 11, superconducting bypass element 15, etc. provided in the superconducting circuit 16 are provided inside the cryostat 18, as in the example shown in FIG.
  • the superconducting first conducting wire 13 related to the superconducting circuit 16 is connected via the HTS power lead 22. It is connected to a power lead 17 that is normally conductive (for example, made of phosphorus-deoxidized copper).
  • the high temperature superconducting HTS power lead 22 is made of a copper oxide superconductor such as REBCO or BSCCO.
  • the connection part 24 (see FIG. 9) between the normal conductive power lead 17 and the high temperature superconducting HTS power lead 22 is thermally anchored to the first stage 33 of the electric refrigerator 31 (see FIG. 9). (see dashed arrow). Furthermore, the low temperature section 26 of the HTS power lead 22 is thermally anchored to the second stage 35 of the electric refrigerator 31 (see the broken line arrow in FIG. 9).
  • an 80K radiation shield is provided inside the cryostat 18 so as to enclose the cryogenic part including the superconducting circuit 16.
  • This radiation shield is attached to the first stage 33 of the electric refrigerator 31.
  • the radiation shield serves to protect the interior of the radiation shield from radiant heat outside the cryostat 18 by keeping it in a cooled state.
  • the superconducting coil 11 and the superconducting bypass element 15 are superconductingly connected to form a superconducting loop via the first conducting wire 13 made of the above-described magnesium diboride (MgB 2 ) superconducting single-core wire. There is.
  • the superconducting coil 11 and the first conducting wire 13 are attached to the second stage 35 of the electric refrigerator 31 using a metal mounting member (non-metallic mounting member) having high thermal conductivity. (see dashed line arrow in FIG. 9). As a result, the superconducting coil 11 and the first conducting wire 13 are conductively cooled.
  • the first conducting wire 13 supplies current to the superconducting loop configured including the superconducting coil 11 and the superconducting bypass element 15, and The low temperature section 26 of the HTS power lead 22 and the superconducting loop are electrically connected.
  • a mounting member 37 made of stainless steel is provided for producing the same.
  • the superconducting bypass element 15 is provided in a thermally coupled state to this mounting member 37.
  • the mounting member 37 is connected integrally to each of the first stage 33 and the second stage 35 of the electric refrigerator 31, but the mounting member 37 is a separate thermal link.
  • Each of the first stage 33 and second stage 35 of the electric refrigerator 31 may be thermally coupled to the mounting member 37 via.
  • FIGS. 10A and 10B are conceptual diagrams showing examples of operating temperature settings for the superconducting bypass element 15.
  • the relationship between the temperature difference and heat flow between two points is equivalent to the relationship between potential difference and current. Therefore, as shown in FIGS. 10A and 10B, the temperature difference between the first stage temperature TH of the electric refrigerator 31 and the second stage temperature TL of the electric refrigerator 31 is distributed using thermal resistance. By doing so, the desired intermediate temperature Tm is achieved. Thermal conductivity exhibits nonlinearity with respect to temperature. Generally, the higher the temperature, the higher the thermal conductivity and the lower the thermal resistance.
  • the intermediate temperature Tm moves toward the first stage temperature TH compared to when there is no heat generation.
  • the effect of reducing the dynamic current capacity can be obtained by current shunting during excitation and demagnetization.
  • the heat transfer paths (first heat transfer path and An intermediate temperature Tm based on the temperature difference between the first stage temperature TH and the second stage temperature TL is set by the thermal resistance in the second heat transfer path (second heat transfer path).
  • the thermal resistance related to the first heat transfer path from the installation location of the electric refrigerator 31 to the first stage 33, and the second heat transfer path from the installation location of the electric refrigerator 31 to the second stage 35 is set by the interaction with the thermal resistance.
  • the temperature dependence of thermal resistance differs depending on the type of material. Therefore, it is preferable to set the thermal conductivity to be different between the first heat transfer path and the second heat transfer path.
  • the intermediate temperature Tm can be brought closer to the first stage temperature TH.
  • FIG. 11 is a conceptual diagram showing a second mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
  • the first mounting state of the superconducting magnet device 10 shown in FIG. 9 and the second mounting state of the superconducting magnet device 10 shown in FIG. 11 have many common parts. Therefore, the differences between the two will be explained in place of the explanation of the second mounting state of the superconducting magnet device 10.
  • the superconducting circuit 16 provided in the superconducting magnet device 10 according to the second mounting state is kept at an extremely low temperature while being enclosed within the refrigerant container 41 containing the liquid refrigerant. is maintained. That is, the superconducting circuit 16 provided in the superconducting magnet device 10 is immersed and cooled with a liquid refrigerant. Note that a part or all of the winding portion of the superconducting coil 11 is directly cooled by the liquid refrigerant. Moreover, the superconducting bypass element 15 is located exposed from the liquid surface of the liquid refrigerant.
  • the superconducting bypass element 15 is thermally coupled to a portion of the refrigerant container 41 existing in the radiation shield 43 room that exhibits a higher temperature than the internal space average temperature.
  • the thermal resistance of the first heat transfer path from the superconducting bypass element 15 to the above-described high temperature portion and the gap between the superconducting bypass element 15 and the superconducting coil 11 The operating temperature of the superconducting bypass element 15 is set based on the thermal resistance of the first conducting wire 13 that electrically connects the superconducting bypass element 15 and the corresponding resistance ratio.
  • FIG. 12 is a conceptual diagram showing a third mounting state of the superconducting magnet device 10 according to the embodiment of the present invention.
  • the second mounting state of the superconducting magnet device 10 shown in FIG. 11 and the third mounting state of the superconducting magnet device 10 shown in FIG. 12 have many common parts. Therefore, the differences between these two will be explained in place of the explanation of the third mounting state of the superconducting magnet device 10.
  • a cooling system that directly cools the superconducting coil 11 using a refrigerant is used as a cooling means
  • the second mounting state of the superconducting magnet device 10 shown in FIG. The three mounting states are the same in that they use a refrigerant as a cooling means, but they are different in that they employ a cooling system that indirectly cools the superconducting coil 11 using a refrigerant.
  • the operating temperature of the superconducting bypass element 15 is set to The temperature is set higher than the ambient temperature related to the coil 11.
  • the heat transfer path from the high-temperature portion to the superconducting bypass element 15 is not limited to a heat transfer path using physical solid-state heat conduction.
  • it may be a heat transfer path using heat transfer by gas such as helium gas, or it may be a heat transfer path using radiation.
  • the current capacity of the superconducting bypass element 15 can be made sufficiently smaller than the current capacity of the superconducting coil 11.
  • FIG. 13 is an explanatory diagram showing a nuclear magnetic resonance diagnostic apparatus 71 using the superconducting magnet device 10 according to the embodiment of the present invention.
  • the nuclear magnetic resonance diagnostic device 70 using the superconducting magnet device 10 according to the embodiment of the present invention is a device that utilizes the nuclear magnetic resonance phenomenon to visualize the internal state of a living body and provide it for diagnosis.
  • the nuclear magnetic resonance diagnostic apparatus 70 includes a bed 73 on which a subject 71 lies in a gap between a superconducting magnet device 10 that includes an upper superconducting coil 11 and a lower superconducting coil 11. is configured to be transported by a transporter 75 so as to be able to move forward and backward.
  • the nuclear magnetic resonance diagnostic apparatus 70 using the superconducting magnet device 10 according to the embodiment of the present invention, the internal state of the living body of the subject M can be visualized and used for diagnosis.
  • the nuclear magnetic resonance diagnostic apparatus 70 has been described as an example of application of the superconducting magnet device 10 according to the embodiment of the present invention, the present invention is not limited to this example.
  • the superconducting magnet device 10 according to the embodiment of the present invention can be applied to any application requiring a temporally stable magnetic field.

Abstract

L'invention concerne un dispositif à aimant supraconducteur (10) qui est équipé d'une bobine supraconductrice (11) et d'une alimentation électrique d'excitation (23) pour exciter la bobine supraconductrice (11). Une résistance de protection (25) et un élément de polarisation supraconducteur (15), qui présente un supraconducteur à haute température en tant que matériau de fil, sont connectés en parallèle à la bobine supraconductrice (11). La capacité de courant de l'élément de polarisation supraconducteur (15) est suffisamment inférieure au courant de fonctionnement nominal de la bobine supraconductrice (11). L'élément de polarisation supraconducteur (15) court-circuite électriquement la bobine supraconductrice (11) dans un état de faible résistance lorsqu'un champ magnétique prédéfini est créé, et, lorsque le champ magnétique change, effectue une opération pour changer spontanément l'état de commutation en passant dans un état de résistance élevée et en changeant la quantité d'alimentation en courant de l'alimentation électrique d'excitation (23) à la bobine supraconductrice (11).
PCT/JP2023/028156 2022-09-02 2023-08-01 Dispositif à aimant supraconducteur et dispositif de diagnostic par résonance magnétique nucléaire WO2024048179A1 (fr)

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JP2022-140393 2022-09-02
JP2022140393A JP2024035738A (ja) 2022-09-02 2022-09-02 超電導磁石装置、及び核磁気共鳴診断装置

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH10294213A (ja) * 1997-04-22 1998-11-04 Hitachi Ltd 酸化物系超電導マグネットシステムの製造方法及び酸化物系超電導マグネットシステム及び超電導磁場発生装置
JP2009273673A (ja) * 2008-05-15 2009-11-26 Mitsubishi Electric Corp 超電導電磁石およびｍｒｉ装置
JP2020068293A (ja) * 2018-10-24 2020-04-30 株式会社東芝 超電導磁石装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH10294213A (ja) * 1997-04-22 1998-11-04 Hitachi Ltd 酸化物系超電導マグネットシステムの製造方法及び酸化物系超電導マグネットシステム及び超電導磁場発生装置
JP2009273673A (ja) * 2008-05-15 2009-11-26 Mitsubishi Electric Corp 超電導電磁石およびｍｒｉ装置
JP2020068293A (ja) * 2018-10-24 2020-04-30 株式会社東芝 超電導磁石装置

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