JP2019220524A - Superconducting magnet and protection method thereof - Google Patents

Abstract

To provide a superconducting magnet capable of rapidly extracting a current when a quench occurs.SOLUTION: A superconducting magnet includes a superconducting coil winding 1, a protection resistor 5, and an excitation power supply 3, and the protection resistor 5 is connected in parallel with the superconducting coil winding 1 with respect to a loop circuit including the superconducting coil winding 1 and the excitation power supply 3. The superconducting coil winding 1 and a heater coil winding 2 are co-wound along the superconducting wire. One end of the superconducting coil winding 1 and one end of the heater coil winding 2 are connected to form a non-inductive current path, and has a quench-back heater power supply 4 for supplying a current to the current path.SELECTED DRAWING: Figure 1

Description

  The present invention relates to superconducting magnets, and in particular, to magnet protection during quench of high-temperature superconducting magnets.

High-temperature superconducting materials can be operated in higher temperature regions without using liquid helium, which is expensive and scarce as a resource. For this reason, superconducting magnets using such magnets have been developed (for example, see Patent Document 1). HTS magnet (hereinafter, referred to as HTS magnet) is not only the advantage of not using a liquid helium, conventional metal-based superconducting magnet (NbTi, Nb 3 _Sn) quenched been a Problem In the (normal conducting transition) Since there is almost no need to worry, it is highly reliable in operating magnets.

  However, once a quench occurs, the quench is an important issue for the superconducting magnet that requires measures (for example, see Non-Patent Document 1). Therefore, when quench occurs, it is necessary to quickly recover magnetic energy from the superconducting magnet to prevent burning of the magnet. For example, a superconducting magnet needs to cut off the current supply from the excitation power supply and quickly recover the stored energy (magnetic energy) of the magnet.

  In the case of a power-supply-type superconducting magnet, when a quench occurs, the occurrence is immediately detected, and the superconducting magnet is immediately disconnected from the excitation power supply. In detecting the quench, the voltage generated in the magnet is constantly monitored, and when the abnormal voltage of the resistance is observed, the operation shifts to the magnet protection operation. As a method of recovering energy, it is common to dissipate it as heat with a protective resistor or diode connected to the magnet circuit, and sometimes a part of the energy is positively converted into heat by the magnet (coil) itself. .

  As a method of actively collecting energy by the magnet itself, there is a method called quench back. In this method, a superconducting coil is equipped with a heater or a structure that generates eddy current due to magnetic field attenuation during quench, and heat is applied to the superconducting coil by an active or passive method during quench, thereby expanding the resistance region of the superconducting coil. It is. This method is applied to a magnet in which energy cannot be recovered quickly from the standpoint of dielectric strength only with a protective resistor installed outside the magnet.

  Conventionally, in superconducting magnets, various quench protection methods have been adopted according to the size and operation mode of the magnet, and are technically established, and there is no possibility of burning the magnet.

Japanese Patent No. 5665634

Takagi et al., "High Sensitivity of HTS Coil Quench Detection Using Co-Wound Coil", Low Temperature Engineering, Vol. 52, No. 1, pp. 44-51, 2017

  Although it is an HTS magnet that requires little attention to the occurrence of quench, there is still the risk of quench occurring due to artificial misolation or unexpected heat input to the magnet. Protection and energy recovery are necessary as with other superconducting magnets. When quench occurs, HTS magnets are adversely affected by the difficulty of quench, and the following problems occur.

  In a conventional superconducting magnet such as NbTi, when quench occurs, the resistance region that has transitioned to normal conduction rapidly expands over the entire magnet (quench propagation). Therefore, a resistive voltage is immediately observed immediately after quenching, and quench detection is easy. However, in a thermally stable HTS magnet having a high critical temperature, the quench propagation speed is low and the resistance region does not expand, so that the voltage generation is extremely small and quench detection is difficult. With the HTS magnet, quenching cannot be detected until the resistance region is enlarged, so that it takes time to detect the quench, and it takes time to shift to the magnet protection operation. Therefore, it is necessary to rapidly recover energy in the HTS magnet in a shorter time than in the conventional superconducting magnet.

  Non-insulated windings (NI (No Insulation) windings) have been proposed for HTS magnets in which it is difficult to detect burnout of the magnets because it is difficult to detect quench. Usually, a superconducting coil in which a wire-insulated superconducting wire is wound is wound in a state where the wire is not insulated. A good conductor such as copper, which is called a stabilizing material, is placed outside the superconducting wire. However, even though a good conductor has a higher resistance than a zero-resistance superconductor, in a steady state, the current flows through the superconducting wire ( Coil). When a quench occurs, the current is shunted to the adjacent superconducting winding so as to bypass the generated resistance, so that the quench can be passively protected.

  However, since this NI coil shunts even in the excitation process, a predetermined current arrangement, a current completely flows only through the superconducting wire, and it takes time to generate a magnetic field as designed, and a large magnet with a large inductance, At present, it cannot be applied to magnets such as MRI (Magnetic Resonance Imaging) and NMR (Nuclear Magnetic Resonance) which require magnetic field uniformity, and cannot be used for applications assuming a fluctuating magnetic field.

  As an example of mounting a quench-back heater on an HTS magnet, there is a 32T magnet developed by the United States National High Magnetic Field Laboratory (NHFML, USA). This magnet is provided with an HTS magnet inside a 15 T metallic superconducting magnet and generates 17 T, for a total of 32 T. The HTS magnet is formed by laminating double superconducting tapes of an oxide superconducting tape wire, and a meander-shaped sheet heater for quenching back is inserted between the pancake coils.

  This HTS magnet has a smaller size and inductance than a whole body MRI and the like, and since it is cooled with liquid helium, it has good cooling characteristics and magnet protection is easy. As the coil becomes larger, the stored energy becomes larger, and it is necessary to shorten the time for collecting the coil in order to prevent burning. At present, no HTS magnet protection system applicable to whole body MRI or the like has been put to practical use.

  An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a superconducting magnet capable of rapidly extracting a current when a quench occurs, and a method of protecting the superconducting magnet.

  In order to achieve the above object, the superconducting magnet of the present invention is a superconducting magnet having a superconducting coil in which a superconducting wire is wound, wherein the superconducting coil is co-wound with a heater wire so as to be along the superconducting wire, One end of the winding of the superconducting coil and one end of the winding of the heater wire are connected to form a non-inductive current path, and a power supply (e.g., quench-back heater power supply 4) for supplying a current to the current path is provided. It is characterized by. Other aspects of the present invention will be described in embodiments described later.

  ADVANTAGE OF THE INVENTION According to this invention, when a quench arises, an electric current can be rapidly extracted.

It is explanatory drawing which shows the basic principle of the superconducting magnet which concerns on this embodiment, (a) is a circuit diagram, (b) is a schematic external view of a superconducting coil. It is a schematic diagram which shows one form of the winding method of this embodiment. It is a schematic diagram which shows one form of the coil cross-sectional configuration of this embodiment. It is a schematic diagram which shows another form of the coil cross-section of this embodiment. It is a mimetic diagram showing other forms of coil section composition of this embodiment, (a) is a case of a round superconductor, and (b) is a case of a rectangular superconductor. It is a circuit diagram showing an example of a quench voltage detection method of the present embodiment. It is a circuit diagram showing another example of the quench voltage detection method of the present embodiment. It is explanatory drawing showing the superconducting magnet of the permanent current mode driving | operation concerning this embodiment. It is explanatory drawing showing the equivalent circuit of the permanent current mode operation | movement magnet of this embodiment.

  The present invention is intended to prevent the magnet from being burned out by simultaneously extracting the current from the HTS magnet from which energy recovery is difficult when a quench occurs and simultaneously heating the entire magnet.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited to the embodiments described here, and can be appropriately combined or improved without changing the gist.

(Basic configuration)
1A and 1B are explanatory diagrams showing a basic principle of protection of a superconducting magnet according to the present embodiment, wherein FIG. 1A is a circuit diagram, and FIG. 1B is a schematic external view of a superconducting coil. The superconducting magnet 100 shown in FIG. 1A has a superconducting coil 21, a protective resistor 5, and an excitation power supply 3. In a loop circuit including the superconducting coil 21 and the excitation power supply 3, the superconducting coil 5 It is connected in parallel with the winding 1.

  The superconducting coil 21 has the heater coil winding 2 co-wound along the superconducting coil winding 1 (superconducting wire), and the inductance of the superconducting coil winding 1 and the inductance of the heater coil winding 2 co-wound are: , So that they are almost equal. Since the coils having the same current path are arranged in close contact with each other, a non-inductive current path is formed when one end of the superconducting coil winding 1 and one end of the heater coil winding 2 are connected by the connection portion 7.

  The superconducting magnet 100 has a quench-back heater power supply 4 (current source, current input means) for supplying a current to the current path. The quench-back heater power supply 4 is connected to a connection 1a of the superconducting coil winding 1 and a connection 2a of the heater coil winding 2.

  In the schematic external view showing the superconducting coil shown in FIG. 1B, a cutout is provided in the upper flange of the bobbin 24 in the radial direction. The connection portions 1a, 2a, 7 are raised from the notches. As described above, the connection portions 1 a and 2 a are connected to the quench-back heater power supply 4, and the connection portion 7 is connected to one end of the excitation power supply 3. Although the quench-back heater power supply 4 is connected in the figure, it is electrically connected at the moment when the current is switched from the superconducting coil winding 1 to the heater coil winding 2 after the quench is detected.

  FIG. 2 is a schematic diagram illustrating one embodiment of the winding method of the present embodiment. FIG. 2 shows the double pancake coil 11 (corresponding to the superconducting coil 21 of FIG. 1). A commercially available yttrium-based superconducting tape material 12 having a width of 4 mm (corresponding to the superconducting coil winding 1 in FIG. 1) and a copper tape material 13 having a thickness of 4 mm and a thickness of 100 μm (corresponding to the heater coil winding 2 in FIG. 1) are wound. It is turned. Although not shown, the superconducting tape material 12 is insulated by a polyimide tape, and the copper tape material 13 is wound without electrical insulation.

  As shown in FIG. 1, the superconducting coil winding 1 and the heater coil winding 2 are coherently wound with the two coils in close contact with each other, so that the self-inductances of the respective coils are substantially equal, and the mutual inductances are also the respective self-inductances. Becomes equal to

  When a quench occurs, a current is supplied from a quench-back heater power supply 4 to a non-inductive circuit composed of a superconducting coil winding 1 and a heater coil winding 2 as shown in FIG. The direction of the current to be supplied was made to be opposite to the direction of the current flowing through the superconducting coil winding 1.

  As the quench-back heater power supply 4, a 1-μF capacitor connected in parallel and charged to 100 V was used. The total length of the coil winding is approximately 140 m. The resistance of the copper tape is about 0.46Ω, and the current is supplied to the heater in the order of 1 millisecond. At the moment when the capacitor was connected, a current of 50 amperes or more was rapidly drawn from the superconducting coil, and at the same time, the entire coil was heated by the quench-back heater to a normal state.

  The method for protecting a high-temperature superconducting magnet (HTS magnet) of the present embodiment aims at preventing magnet burning during quench. That is, as shown in FIG. 2, the superconducting coil 21 has the superconducting coil winding 1 and the heater coil winding 2 co-wound, and the superconducting coil winding 1 and the heater coil winding 2 constitute a non-inductive circuit. ing. By applying a current to this non-inductive circuit in the opposite direction to the current flowing in the superconducting coil when a quench occurs, the current in the superconducting coil is withdrawn, and at the same time, the quench heater is energized to promote the generation of resistance for the entire coil. Can be.

  The superconducting magnet 100 according to the present embodiment is a superconducting magnet having a superconducting coil in which a superconducting wire is wound. One end of the wire is connected to one end of the winding of the heater wire to form a non-inductive current path, and has a power supply (for example, a quench-back heater power supply 4) for supplying a current to the current path.

  The superconducting magnet 100 of the present embodiment has a superconducting coil in which a superconducting wire is wound. In the superconducting coil, a heater wire is co-wound along the superconducting wire, and the superconducting coil is mounted so that the inductance of the co-wound heater wire and the inductance of the co-wound heater wire are substantially equal. Since the coils having the same current path are arranged in close contact with each other, a non-inductive current path can be formed by connecting one end of the winding of the superconducting coil and one end of the heater winding.

  With respect to the non-induction winding, current can be taken in and out at high speed without generating an induction voltage. Therefore, a heater wire is co-wound around the superconducting coil, one end of the co-wound windings is connected to form a non-guided path, and a power supply for supplying current to the non-guided path is provided. Accordingly, it is possible to input / output current to / from the superconducting coil at a high speed and simultaneously input / output current to / from the heater winding.

  When a current is applied to the non-induction current path in a direction opposite to the current flowing in the superconducting coil, the current flowing in the superconducting coil looks as if it has moved to the heater winding. The only task performed by the power supply is to move current from the superconducting coil side to the heater winding.

  Since the current of the superconducting coil is suddenly drawn to the heater side, it is possible to instantaneously reduce the current value at the quench occurrence location. When a quench occurs, the current versus voltage characteristic (current-voltage characteristic) of the superconducting wire can be described by a power law, so lowering the current value has the effect of significantly reducing the amount of heat generated at the quench occurrence location. It is effective in preventing burnout of superconducting magnets.

  Since the power supply basically performs only the task of transferring the current from the superconducting coil to the heater, the power supply has no effect on the magnet when viewed macroscopically. Even if the current is switched, the total current of the magnet does not change, so that the electromagnetic force acting on the magnet does not change.

(Heater wire)
For the co-wound heater wire (heater coil winding 2), various materials can be selected according to the size of the magnet and the function to be added to the heater wire. In the case of a conduction cooling magnet that performs heat conduction cooling, it is possible to improve the heat conduction inside the windings of the magnet by using copper or aluminum, which is a good thermal conductor, as the heater wire.

  In addition, since these conductors have a small electric resistance, a larger current can be transferred from the superconducting coil side, and the quenched current of the superconducting wire is greatly extracted, so that the effect of preventing burnout is high. It is also possible to have a reinforcing effect on hoop force (electromagnetic force) by co-winding a high-strength material such as stainless steel, iron, and Hastelloy with high Young's modulus as the heater wire.

  Further, in a magnet that requires a rapid increase in the temperature of the superconducting winding, it is possible to use manganin, constantan, or nichrome, instead of copper, as a high-resistance heater wire so as to generate more heat. Manganin, constantan, and nichrome are materials whose electrical resistivity is at least one order of magnitude higher than copper. However, this is a case where the heater driving power source is a constant current source. It is also appropriate to use a high-resistance heater wire when the heater power supply is a constant voltage source or when limiting the current so as not to increase.

  It is also important to prevent the burnout by rapidly extracting the current from the superconducting coil and simultaneously instantaneously and uniformly raising the temperature of the superconducting coil to a resistance state. For that purpose, it is essential that the superconducting coil winding and the heater winding are installed close to each other and are thermally connected well.

  As shown in FIG. 2, when the superconducting wire is a tape-shaped conductor (for example, see superconducting tape 12), the co-wound heater wire (for example, copper tape 13) is also a tape-shaped conductor, This can be realized by winding. If the superconducting wire has a round or rectangular cross section, it is desirable that the heater windings have substantially the same dimensions in order to obtain good thermal contact. This will be described with reference to FIGS. Note that FIGS. 3 and 4 are different forms from FIG.

(Improved thermal conductivity of coil)
FIG. 3 is a schematic diagram illustrating one embodiment of the coil cross-sectional configuration of the present embodiment. FIG. 3 shows a coil winding cross section for improving the heat transfer in the radial direction (r direction) of the superconducting coil 21. Here, an embodiment using MgB ₂ rectangular wire as a superconducting wire will be described. The superconducting coil 21 is formed by winding a rectangular superconducting conductor 22 and a round or rectangular heater conductor 23 around a bobbin 24 along a superconducting wire. The dimensions were selected such that the radial thickness (wire thickness) of the superconducting wire and the heater wire was the same, and two wires were wound. The heater wire was aluminum. The layers were arranged and wound so that the aluminum heater wires of each layer almost overlapped.

  In order to improve the heat conduction of the coil winding using a good conductor as the heater wire, the heater windings need to be in contact with each other. When trying to improve the heat conduction in the radial direction of the coil winding, the thickness of the heater wire in the radial direction should be equal to or greater than the thickness of the superconducting wire, so that the heater wire overlaps in the layer direction. This can be realized by winding.

  That is, in FIG. 3, when the cross-sectional dimension in the radial direction of the superconducting coil around which the superconducting wire is wound is defined as the wire thickness, the wire thickness of the superconducting wire and the wire thickness of the heater wire are substantially equal. The heater wire is a good heat conductor, and is wound so as to contact each other in the radial direction of the superconducting coil between the heater wires. Thereby, the heat conduction characteristics of the coil in the radial direction can be improved.

FIG. 4 is a schematic diagram illustrating another embodiment of the coil cross-sectional configuration of the present embodiment. FIG. 4 is a different form from FIG. FIG. 4 shows a cross section of a coil winding for improving the heat transfer in the axial direction (Z-axis direction) of the superconducting coil 21 in FIG. Here, an embodiment using MgB ₂ rectangular wire as a superconducting wire will be described. The superconducting coil 21 is formed by winding a rectangular superconducting conductor 22 and a round or rectangular heater conductor 23 around a bobbin 24 along a superconducting wire. The dimensions were adjusted so that the axial width (wire width) of the superconducting wire and the heater wire was the same, and the wire was wound. The heater wire was aluminum. The winding machine was devised so that aluminum was wound after the superconducting wire was wound, and the superconducting wire was adjusted to be pressurized by aluminum. The superconducting winding maintains good thermal contact during operation due to the effects of aluminum preload and thermal shrinkage.

  In order to improve the heat conduction of the coil winding using a good conductor as the heater wire, the heater windings need to be in contact with each other. This can be realized by winding the coil so that the heater wire contacts the heater wire in the axial direction by making the width of the heater wire in the axial direction substantially equal to or wider than the width of the superconducting wire.

  That is, in FIG. 4, when the axial cross-sectional dimension of the superconducting coil around which the superconducting wire is wound is defined as the wire width, the wire width of the superconducting wire is substantially equal to the wire width of the heater wire. The heater wire is a good heat conductor, and the heater wires are wound so as to be in contact with each other in the axial direction of the superconducting coil between the rows of the heater wires. Thereby, the heat conduction characteristics of the coil in the axial direction can be improved.

(Coil current density drop suppression)
Since the heater winding lowers the coil current density, it is preferable that the heater winding is not provided from the viewpoint of generating a magnetic field. When the cross-sectional shape of the superconducting wire is round or rectangular, a gap is formed in the coil winding. By winding the heater wire using this gap, it is possible to suppress a decrease in coil current density. .

  FIG. 5 is a schematic diagram illustrating another embodiment of the coil cross-sectional configuration of the present embodiment. The rectangular or round superconducting conductor 22 is widely used in superconducting magnets, and the coil current density can be suppressed by installing a heater winding in accordance with the R portion of the conductor.

  FIG. 5A shows a case where a round superconducting conductor 22 and a round heater conductor 23 are used. When the cross-sectional shape of the superconducting conductor 22 is round, a gap is formed in the coil winding. By winding the heater conductor 23 using this gap, it is possible to suppress a decrease in coil current density. It is.

  FIG. 5B shows a case where a rectangular superconducting conductor 22 having a predetermined curvature at corners formed at four corners of a rectangular cross section and a round heater conductor 23 are used. If the cross-sectional shape of the superconducting conductor 22 is a rectangular shape having a predetermined curvature at the corners formed at the four corners of the rectangular cross section, a gap is formed in the coil winding. By winding, it is possible to suppress a decrease in coil current density.

  That is, in the superconducting magnet 100 of the present embodiment, the cross-sectional shape of the superconducting wire is a round shape or a flat rectangular shape having a predetermined curvature at a corner, and the superconducting coil around which the superconducting wire is wound has a gap between the superconducting wires. , And a heater wire. Thereby, it is possible to suppress a decrease in coil current density.

(Quench back heater power supply)
As shown in FIG. 1, the power supply needs to be always on standby in order to supply a current to the non-guide path. Since the power supply capacity is only required to transfer the current from the superconducting coil to the heater, it is possible to cope by holding the necessary energy in the capacitor bank. Of course, an active power supply may be kept on standby for quench protection.

(Energy recovery)
The present invention is characterized in that a current is immediately applied to the heater winding from the superconducting coil winding to prevent local burning of the superconducting winding. Is the same as When the quench is detected, the excitation power supply 3 is separated from the magnet and energy recovery of the magnet is performed, but energy of both the superconducting coil winding and the heater winding is recovered. The energy of the magnets distributed to the superconducting coil winding and the heater winding is recovered by a resistor, a diode, or the like appropriately installed in each winding (not shown). The quench-back power supply is used to perform the work of switching the current, and does not essentially contribute to the recovery of the stored energy of the entire magnet, but actively distributes and recovers the amount of energy recovery by the active power supply. It is also possible to recover energy on the control and power supply side.

(Quench detection)
FIG. 6 is a circuit diagram illustrating an example of the quench voltage detection method according to the present embodiment. In order to detect a very small quench voltage, it is essential to improve the S / N of the voltage detection system. FIG. 6 shows a so-called co-winding method in which an inductive voltage is canceled using a co-winding heater wire, and the quench detector 6 detects a quench voltage.

  FIG. 7 is a circuit diagram illustrating another example of the quench voltage detection method of the present embodiment. FIG. 7 shows a midpoint balance voltage method in which the balance voltage between the heater wire and the superconducting wire is measured at the midpoint of the superconducting coil having the co-wound heater wire. The mid-point balanced voltage method not only cancels inductive noise, but also cancels voltage noise originating from the power supply and voltage caused by the time change of magnetization inside the superconducting device, generating a very small quench voltage. Can be detected and the operation can be shifted to the magnet protection operation in a very short time after the occurrence of the quench, which is extremely effective in preventing magnet burning.

  In the case of the midpoint balance method, the switch 8 turns on the superconducting coil winding 1 and the heater coil winding 2 during normal operation, and the quench detector 6 measures the balance voltage. When a quench is detected, the voltage supplied from the quench-back heater power supply 4 opens the switch 8 so that a short-circuit current does not flow through the switch 8, and then a current flows from the superconducting coil winding 1 to the heater coil winding 2. Current is supplied from the quench-back heater power supply 4 in order to replace the current.

  It is necessary to rapidly extract energy from the magnet and perform quench back in order to prevent burning, but it is important how quickly quench detection that triggers this operation is performed. By using the co-wound heater winding, it is possible to cancel the induced voltage (noise) of the magnet itself, which is an obstacle to quench voltage detection. I do.

(Permanent current mode)
FIG. 8 is an explanatory diagram illustrating the superconducting magnet in the permanent current mode operation according to the present embodiment. Although the application example of the present invention has been shown for a magnet operated in a state connected to a power supply (drive mode magnet), the present invention is most effective only in a permanent mode operation which is operated while being disconnected from the power supply. is there. FIG. 8 shows a schematic circuit of the magnet in the permanent current mode. In the persistent current mode operation, both ends of the coil are electrically closed by a superconducting switch called a persistent current switch (PCS), that is, a switch having zero electrical resistance, after a current is supplied to the magnet, thereby forming a current loop. , Then the excitation power supply is removed.

  In the magnet in the drive mode operation, it is possible to shift to the energy recovery state of the magnet by immediately disconnecting the excitation power supply 3 from the magnet after the quench detection, and it is also easy to install an external resistor for recovering energy. On the other hand, in the permanent current mode operation, since it is necessary to heat the heater to turn off the PCS (resistance state), it takes time to shift to the energy recovery state, and the PCS itself recovers the energy of the magnet. Lacks resistance and heat capacity. Therefore, protection of the HTS magnet in the permanent current mode operation is significantly more difficult than in the drive mode operation.

FIG. 9 is an explanatory diagram illustrating an equivalent circuit of the permanent current mode operation magnet of the present embodiment. FIG. 9 shows an equivalent circuit of FIG. The superconducting coil winding 1 and the heater coil winding 2 are magnetically tightly coupled, and almost L ₁ = L ₂ = M. Therefore, the current supplied from the quench-back heater power supply 4 almost passes through L ₁ and L ₂ , and therefore, even in the permanent current mode operation, the current of the permanent current loop flowing through L ₁ (superconducting coil winding) It is possible to replace I with L ₂ (heater winding).

  However, simply recovering the current from the heater coil winding 2 and installing an external resistor (not shown) in the heater winding and consuming the current with this resistance does not sufficiently recover the energy of the magnet. When the resistance on the superconducting coil winding side is small and the resistance on the heater winding side is larger than that (that is, when the superconducting coil winding side is in a superconducting state), the current transferred to the heater winding is superconducted through magnetic coupling. This is because it is returned to the coil winding side. Therefore, in order to perform energy recovery in the persistent current mode operation, the superconducting coil winding needs to be in a resistance state.

  In the present invention, the heater coil winding 2 has a role as a quench heater for making the superconducting coil winding 1 in a resistance state, and can simultaneously and instantaneously heat the entire coil. A part or all of the current flowing through the superconducting coil winding 1 is transferred to the heater coil winding 2, and the superconducting coil winding 1 is heated and transitions to a resistance state, thereby starting the energy recovery of the magnet. It is necessary to wait until the temperature of the superconducting coil winding rises to a resistance state. However, since a part or all of the current flowing through the superconducting coil winding 1 has been replaced by the heater coil winding 2, Local heat generation at the quench point in the superconducting coil winding can be suppressed, and burnout can be prevented.

  The quench-back heater power supply 4 serves as a trigger for creating a trigger for energy recovery in the permanent current mode operation magnet. By actively controlling the quench-back heater power supply 4, the energy recovery on the heater coil winding 2 side is performed. The distribution of the amount of energy recovery in the circuit and the distribution of the amount of energy recovery in the current circuit on the superconducting coil winding side can be adjusted, and energy can be recovered under optimal energy recovery conditions. In the permanent current mode operation state, when a constant current is supplied from the quench-back heater power supply 4, the stored energy of the magnet does not change, and the energy input from the power supply is used for the work of raising the temperature of the magnet. . In permanent current mode operation in which energy cannot be recovered by external resistance, energy is recovered using the heat capacity of the magnet itself, so inputting extra energy from outside leads to a rise in the temperature of the magnet. Not desirable. By actively controlling the quench-back heater power supply 4, it becomes possible to optimally control the energy input for bringing the superconducting coil winding 1 into a resistance state.

  These methods enable magnet protection for HTS magnets that are difficult to detect quench and do not take time for energy recovery and quench back for magnet protection.

  The superconducting magnet 100 of the present embodiment can be applied to any high-temperature superconducting magnet, and is particularly suitable for applications requiring a high-precision magnetic field such as MRI and NMR, and applications requiring reproducibility of the magnetic field such as magnets for accelerators.

1 Superconducting coil winding (superconducting wire)
2 Heater coil winding (heater wire)
3 Excitation power supply 4 Quench-back power supply (power supply, current input means)
5 Protection resistor 6 Quench detector (voltmeter)
7 Connecting part 8 Switch 11 Double pancake coil 12 Superconducting tape material 13 Copper tape material 21 Superconducting coil 22 Superconducting conductor 23 Heater conductor 24 Bobbin 100 Superconducting magnet

Claims (12)

A superconducting magnet having a superconducting coil wound with a superconducting wire,
In the superconducting coil, a heater wire is co-wound along the superconducting wire,
One end of the winding of the superconducting coil and one end of the winding of the heater wire are connected to form a non-inductive current path, and a power supply for supplying a current to the current path is provided. . The material of the heater wire is any of copper and aluminum,
Or, the material of the heater wire is any of stainless steel, iron, Hastelloy,
Alternatively, the material of the heater wire is any of manganin, constantan, and nichrome. The superconducting magnet according to claim 1, wherein The superconducting magnet according to claim 1, wherein both the superconducting wire and the heater wire are tape-shaped conductors. The cross-sectional shape of the superconducting wire is a round shape or a rectangular shape having a predetermined curvature at a corner, and the superconducting coil wound with the superconducting wire has the heater wire disposed in a gap between the superconducting wires. The superconducting magnet according to claim 1, wherein: The wire thickness of the superconducting wire and the wire thickness of the heater wire are substantially equal when a cross-sectional dimension of a wire in a radial direction of the superconducting coil around which the superconducting wire is wound is a wire thickness. The superconducting magnet according to 1. The heater wire is a good heat conductor, and the heater wires are wound so as to be in contact with each other in a radial direction of the superconducting coil between layers of the heater wire. Superconducting magnet. The wire width of the superconducting wire and the wire width of the heater wire are substantially equal when a wire cross-sectional dimension in the axial direction of the superconducting coil around which the superconducting wire is wound is a wire width. The superconducting magnet as described. The heater wire is a good heat conductor, and the heater wires are wound so as to be in contact with each other in an axial direction of the superconducting coil between rows of the heater wires. Superconducting magnet. The superconducting magnet according to claim 1, wherein a power supply for supplying a current to the current path is a capacitor. The superconducting magnet according to claim 1, wherein a power supply for supplying a current to the current path is controlled, and a current distribution amount flowing through the superconducting coil and the heater wire is controlled. The superconducting magnet according to any one of claims 1 to 10, wherein the co-wound heater wire is used as a winding for quench detection. A method for protecting a superconducting magnet having a superconducting coil in which a superconducting wire is wound,
In the superconducting coil, a heater wire is co-wound along the superconducting wire,
One end of the winding of the superconducting coil and one end of the winding of the heater wire are connected to form a non-inductive current path,
A method for protecting a superconducting magnet, wherein a current flowing in the current path in a direction opposite to a current flowing through the superconducting coil during a steady operation is supplied as protection when a quench occurs.

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