JPH0511644B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a superconducting device, and in particular to a persistent current switch that is composed of a plurality of superconducting coils and is used by being switched between a normal conducting state and a superconducting state. The present invention relates to a superconducting device equipped with a superconducting device.

[Conventional technology]

Conventionally, in a superconducting device consisting of a plurality of superconducting coils, as described in Japanese Patent Publication No. 50-1794,
Generally, one gate wire is applied to each superconducting coil, and these gate wires are bundled in parallel to form one thermal persistent current switch (hereinafter abbreviated as permanent switch).

The prior art will be explained in detail with reference to FIG. FIG. 2 shows a case where there are two superconducting coils. As shown in the figure, the lead wires 7+ to 2+ and 7- to 2-, and 7+' to 2+' and 7-' to 2-' of the superconducting coils 1 and 1' are connected to the gate wires of the permanent switch 5 (from the superconducting wires). ) 3 and 3' are connected (by spot welding or crimping) at the lead wire tips 2+, 2- and 2+', 2-'. The gate lines 3 and 3' are connected to a common electrically insulated heater 4.
When heated, it becomes a normal conductor, and when not heated, it becomes a superconductor. The power supply for the heater 4 is indicated by 8.
With the permanent switch 4 open (on; the gate wires 3 and 3' are heated by the heater 4 and made into a normal conductive state), the superconducting coils 1 and 1' are independently excited by the power supplies 6 and 6', and both superconducting coils 1 and 1' are excited independently by the power supplies 6 and 6'. When the currents in coils 1 and 1' reach respective predetermined values, the permanent switch is closed (off;
When the gate lines 3 and 3' are returned to the superconducting state) and the power supplies 6 and 6' are turned off, the persistent current becomes 1→
7-→2-→3→2+→7+→1 and 1'-→7
-'→2-'→3'→2+'→7+'→1' The flow circulates in the closed circuit. At this time, the current flowing through the superconducting coils 1 and 1' flows through the gate lines 3 and 3'. Usually the gate wire is heated,
When the state becomes normal conductivity, it is necessary to increase the resistance value as much as possible, so the superconducting wires used for gate lines 3 and 3' are partially coated with high-purity copper or aluminum for stability. What was removed or
Those coated with high-resistance metals, such as cypronickel, have been used. Therefore, stability is significantly impaired, and a wire having a larger current capacity than the superconducting wires wound around the superconducting coils 1 and 1' is required. As the number of superconducting coils increases, gate wires with large current capacity must be wound into the permanent switch, which not only increases the size of the permanent switch and makes it considerably difficult to manufacture.
This causes an increase in its heat capacity. In order to avoid increasing the size, a method has been adopted in which a plurality of permanent switches with a small number of gate lines are used.

[Problem that the invention seeks to solve]

The drawbacks of the above-mentioned prior art are the large size of the permanent switch and the instability of the gate line. Regarding the former, the key is to increase the heater input to make the permanent switch operate more accurately, that is, to increase the amount of coolant (liquid helium) consumed during the excitation of the supercurrent coil, and to install the permanent switch in the device. spatial constraints arise. Regarding the latter, spatial constraints are imposed on increasing the current capacity of the gate line and where it is installed (low magnetic field region).

The present invention has been made in view of the above-mentioned points, and its purpose is to increase the number of gate wires even if it is equipped with a plurality of superconducting coils, that is, to increase the size of permanent switches. It is an object of the present invention to provide a superconducting device that solves the above problems, improves the stability of the permanent switch, that is, improves the reliability of the permanent switch, and alleviates restrictions on its installation location.

[Means for solving problems]

The above objective is achieved by connecting the lead wire of each superconducting coil to a shared gate line, but when connecting, the current flowing through each superconducting coil is minimized, or It is more effective if the polarities of the power supplies of the superconducting coils are opposite to each other.

[Effect]

In the present invention, only one gate wire is required even though there are multiple superconducting coils, and the maximum value of the current flowing through the gate wire can be selected to be less than the current value of the superconducting coil through which the maximum current flows. Therefore, the permanent switch can be made smaller and more stable at the same time.

〔Example〕

Hereinafter, the present invention will be explained in detail based on illustrated embodiments. FIG. 1 shows an embodiment of a superconducting device of the present invention, and first the overall configuration will be explained. Furthermore, the first
Although the figure shows a case where there are two superconducting coils, the same explanation can be made in the case where there are a plurality of superconducting coils.

As shown in the figure, a power source 6 with the illustrated polarity is connected to the superconducting coil 1 at points 7+ and 7- in the middle of the lead wire. Since these connection points 7+ and 7- are connected by soldering, they have a large heat capacity and become a kind of heat reservoir. This is because the wires between the power supply 6 and the connection point 7+ and between the power supply 6 and the connection point 7- are wired with normal conductive wires, so heat is generated during energization, conduction heat from the wire side, and permanent switch 5 as described later. When turned on,
It functions to prevent heat generation and conduction heat in the normal conduction region near the gate wire 3 and the point 2 at the tip of the lead wire from being conducted to the superconducting coil 1 side. The main part of this circuit is that the lead wires of both superconducting coils 1 and 1' are connected to the gate wire 3 at point 2, and the heater 4' is connected in series with the heater 4 that heats the gate wire 3 of the permanent switch 5. It is configured so that a part of the lead wire can be heated. The superconducting coil 1' has the same construction except that the polarity of its power source 6' is reversed from that of the superconducting coil 1.

Next, the operation of the device will be explained. First, start the power supply 8 of the permanent switch 5, and turn on the permanent switch 5.
When turned on, the heaters 4 and 4' simultaneously heat the gate wire 3 and the lead wires of both superconducting coils 1 and 1', bringing them into a normal conducting state. In this state, the power supplies 6 and 6' are started (it is not necessary to start them at the same time) to excite the superconducting coils 1 and 1'. Most of the current in power supplies 6 and 6' is 6→7+→1→7−→
6 and 6' → 7-' → 1' → 7+' → 6', and a part of the minute current (resistance value in the normal conduction region of the lead wire, inductance of superconducting coils 1 and 1', and resistance of permanent switch 5) (determined by the value) is mutually shunted to the superconducting coil on the other side of the gate line 3.
The current that is shunted to the lead wire additionally heats the part that is still in a superconducting state, contributing to an increase in its resistance and, in fact, becoming a desirable presence. In other words, this is because the normal conductivity region is expanded more than when heated by the heater, resulting in an increase in resistance, and at the same time, the current is suppressed from being shunted to the superconducting coil on the other side. The propagation of this normally conductive region is stopped at the connection points 7+, 7-, 7+', and 7-', which serve as the aforementioned heat reservoirs. The resistance generated in the superconducting coil lead wire in this way is generally caused by a permanent switch.
Although the resistance value is considerably smaller than the resistance value when it is on, it has the function of suppressing the aforementioned shunting. This is because when viewed from the power supply 6, the permanent switch 5 is on.
At the time of , superconducting coils 1 and 1' are connected in parallel, and since resistance is generated in the lead wire in 1' compared to superconducting coil 1, most of the excitation current flows into superconducting coil 1, This is because only a minute current flows through '. This minute current stops sweeping the power source 6, and after a while, gradually returns to the superconducting coil 1. The time depends on the time constant determined by the resistance of the lead wire and the inductance of the superconducting coil 1. If the inductance is small and the predetermined number is large, this minute current value can be ignored, and the current flowing through the superconducting coil can be made equal to the power supply current at the same time as the sweep of the power supply is stopped. Needless to say, the same argument holds true when viewed from the power source 6'.

Now, when the current flowing through the superconducting coils 1 and 1' approaches the desired value and ', if the power supplies 6 and 6' are stopped, the current will be shunted to the gate line 3 and the other superconducting coil as described above. The current decays according to the circuit time constant and disappears over time.
During this time, when the magnetic fields generated by both superconducting coils 1 and 1' reach a desired value, the permanent switch 5 is turned off.
All parts that were in a normal conductive state are brought into a superconducting state. Next, by turning off the power supplies 6 and 6', the persistent current will change from 1 to 7 at the desired values and ', respectively.
−→2′→3→2→7+→1 and 1′→7+′→2→
It begins to flow in a closed circuit of 3→2'→7-'→1→. Therefore, only a current of |-'| flows through the gate line 3.

To further explain the operation of the circuit of the present invention, the permanent switch 5 is turned off, and then the power supplies 6 and 6' are turned on.
Until the circuit is turned off, that is, even when all circuits are in the superconducting state and the stopped power supply is connected, the closed circuit 1→7−→2′→7
-'→1'→7+'→2→7+→1, no current flows that would transfer energy from the superconducting coil with larger magnetic energy to the one with smaller magnetic energy. When the magnetic energy of superconducting coil 1 is greater than that of superconducting coil 2 and >', the current value is > even after a sufficient period of time has passed.
``>'' does not flow as a persistent current. This is because the gate wire of the permanent switch is wound without induction and is short, so both superconducting coils are short-circuited by the gate wire with zero inductance. To explain further, when the persistent current state is reached, there is no voltage anywhere in the circuit, and when >', the current in superconducting coil 1 decreases, and the current in superconducting coil 1' decreases. We cannot think of any mechanism that would increase ′. Also, the power supply 6 is in a persistent current state.
Even when 6' and 6' are passing constant current and ', respectively, there is no place where a finite voltage exists in a closed circuit that is in a superconducting state. Therefore, only a current with a maximum value of |-'| always flows through the gate line 3. The above can be verified experimentally. By installing Hall elements in both superconducting coils 1 and 1' and observing the magnetic field instead of observing the current, the current flowing in the gate line can be determined by |
−′| can be easily confirmed. Below, we will discuss the results of experiments conducted on a system consisting of two small superconducting coils. The superconducting wire wound into the superconducting coil is an ordinary ultrafine multi-core wire (271 Nb-Ti filaments with a diameter of 50 μm embedded in a copper matrix, with a copper-to-superconductor ratio of 2 and a diameter of 1.43 mm). Both superconducting coils
This wire is wound into a cylindrical solenoid shape with an inner diameter of 20 mm, an outer diameter of 50 mm, and a height of 80 mm for ~60 m to create an inductance.
It is a coil with a magnetic field coefficient of 0.018T/A and 2.7mH.
The permanent switch gate wire is 0.25mm in diameter.
Diameter of one Nb-Ti filament coated with copper
A 0.33mm superconducting single core wire is used, and the superconducting filaments are 4mm long at a 10mm pitch in the length direction of the wire.
The copper coating was peeled off intermittently to expose it. The 0.8m length was wound into a coil without induction.
A manganin heater was wrapped inside it, and it was impregnated with epoxy resin and solidified, making it a permanent switch. The superconductor cross-sectional area ratio of the superconducting coil wire and this gate line superconducting wire is ~11:1. Connect these as in the embodiment shown in Fig. 1, bundle the parts (~1 m) corresponding to lead wires 7+~2 and 7+'~2 of both superconducting coils, and connect manganin over a 1 cm section from above. Wrap the heater wire around it and harden it with epoxy resin. Additionally, a Hall element was placed at the center of both superconducting coils. In this state, electricity was applied according to the operating procedure described above. In other words, with 0.9W of heat applied to the permanent switch and 0.2W of heat applied to the lead wire,
Both superconducting coils were excited to 200A. In order to see the magnitude of the resistance value generated in the lead wire and its effect, we stopped connecting a protective resistor in parallel to both superconducting coils and kept the current flowing to 200A. The magnetic field generated by both superconducting coils at the time when the sweep of the applied current was stopped was 3.6 T, which almost matched the calculated value.
The resistance value of the permanent switch is a value measured separately.
It was 3.9Ω. Also, assuming that the specific resistance of copper is 3×10 ^-8 Ωcm, the resistance value generated in the lead wire is:
It is estimated that the maximum resistance across both lead wires is 5.6×10 ^-4 Ω, and the circuit time constant is considered to be a minimum of 4.8 seconds. Since the generated magnetic field matched the calculated value when the power supply stopped sweeping, the circuit time constant is considered to be short and close to the estimated value of 4.8 seconds. Also,
It can also be easily understood from this result that the current flowing through the lead wire is almost zero. If a current flows through the lead wire and flows into the superconducting coil on the other side, the generated magnetic field should not match the calculated value. Therefore, the slight resistance in the lead wire 5.6
×10 ^-4 Ω, it is judged that there is no interference between the currents of both superconducting coils. The time course of the above experiment is shown in Figure 3 in terms of the power supply currents of both superconducting coils and the Hall element output voltage (converted to a magnetic field).
This is the result when both power supplies were operated for 10 minutes, then stopped, and then the permanent switch was turned off after ~11 minutes. The results for superconducting coil 1 are shown at the top of the graph, and the results for superconducting coil 1' are shown at the bottom. Both have short time constants, so
No interference was observed between the currents (magnetic fields) of both coils.

In this experiment, the inductance of superconducting coils 1 and 1' was small, so there was almost no problem, but superconducting coils that can be excited quickly,
In a superconducting coil with a large inductance, if the resistance of the lead wire cannot be increased, the time constant becomes large and the magnetic field generated by the superconducting coil may not follow the power supply current. In other words, interference occurs in the current between both superconducting coils.
Therefore, it is necessary to increase the resistance of the lead wire within an allowable range and to select an excitation speed within a range that does not cause interference with the current. To eliminate this inconvenience,
The following methods can be considered.

Another embodiment of the present invention will be described with reference to FIG. FIG. 4 shows a case where there are four superconducting coils, and the operation thereof is the same as that explained in FIG. 1, so only the configuration thereof will be explained here. Basically, lead line 7 in Figure 1
+~2, and a part of 7+'~2 as gate lines 3+',
The only difference is that 3-' is replaced with a normal permanent switch 45'. Therefore, in this embodiment, two permanent switches are required. The first permanent switch 5 is no different from that in FIG. Second permanent switch gate line 3+'
and 3-' are collectively connected to the gate line 3 of the first permanent switch 5 at a point 2. One lead wire of the superconducting coils 1, 1', 1'', 1 is the first
are collectively connected to one end 2' of the gate wire 3 of the permanent switch 5, and the superconducting coils 1 and 1''
The lead wire of the second permanent switch 5'a is connected to one end 2+'' of the gate line 3+', and the lead wires of the remaining superconducting coils 1' and 1'' are connected to the one end 2+'' of the gate line 3-' of the second permanent switch 5'a.
-'' points.Other configurations are the same as in the case of FIG. A power supply 6 with polarity as shown in
6′, 6″, and 6 are connected to each superconducting coil 1 to 1, the current flowing in these gate lines can be the algebraic sum of the current flowing in each superconducting coil, and its current capacity, that is, the superconducting conductor It is allowed to reduce the cross-sectional area.

As shown in the previous experimental example, the resistance of the gate wire of the permanent switch (3.9 Ω) can be easily increased compared to the resistance of the lead wire (5.6 × 10 ^-4 Ω), so even if the inductance of the superconducting coil is large, the current It becomes extremely easy to cut off the interference.

The number of permanent switches increases by one compared to Figure 1, but
Even if the number of superconducting coils increases further, it is only necessary to connect their lead wires to the 2' and 2+'' points or the 2' and 2-'' points, and the number of permanent switches increases to 2 or more. Never. The size of the permanent switch can also be made extremely small because a gate line with a small current capacity is used.

In Fig. 4, when connecting the superconducting coils 1 to 1'' to the gate lines 3, 3+', and 3-' so that the algebraic sum of the currents flowing through each superconducting coil 1 to 1'' becomes the minimum, Of course, if the generated magnetic field is not directed in the desired direction, the winding direction of the superconducting coil can be reversed. Also,
It is also possible to integrate the permanent switches 5 and 5' into a permanent switch incorporating three gate lines.

In the two embodiments described above, a permanent switch having one or three gate lines can realize a persistent current state with different current values for a plurality of superconducting coils, and the current capacity of the gate line can be can also be an algebraic sum of the currents flowing through each superconducting coil, making it possible to reduce the capacity and significantly improve its stability.

In addition, within the above-mentioned range, the structure, material, and manufacturing method of the gate wire, the configuration of the permanent switch, the method of connecting the heater 4 and other heaters 4' to the power source 8, and the method of connecting the superconducting coils 1 to 1 to the excitation power source 6 to Locations 7+ to 7-' where they are connected to lead wires 6 and their heat capacity, structure of the openings of superconducting coils 1 and 1',
There are no restrictions on the selection of the heating method, heating location, or polarity of the power sources 6 and 6'.

The present invention can be used, for example, by MRI (nuclear magnetic resonance tomography).
The effects will be described when applied to a device. Generally, MRI equipment needs to generate a highly uniform and stable magnetic field over a long period of time.
Combining multiple (3 to 5) superconducting coils,
They are operated in persistent current mode. By adopting the configuration as already described in the embodiment, basically one gate line is required, and it is possible to downsize the permanent switch and reduce the current capacity.
The expected effects include improved manufacturability and reliability of permanent switches, reduction of permanent switch heater input, simplification of the overall device configuration and improved operability, and reduction in the amount of liquid helium charged and consumed. , the industrial effects in related fields are considered to be extremely large.

[Effects of the Invention] According to the superconducting device of the present invention described above, the lead wire of each superconducting coil is connected to one shared gate wire, and at the time of this connection, the current flowing through each superconducting coil is Since the polarity of each power source of the superconducting coils is opposite to each other, even if there are multiple superconducting coils, only one gate line is required.
Since the maximum value of the current flowing through the gate wire can be selected to be less than the current value of the superconducting coil that flows the maximum current, the permanent switch can be made smaller, and
This increases stability and improves reliability, which is very effective for this type of superconducting device.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the superconducting device of the present invention, and shows a wiring diagram when there are two superconducting coils, and Fig. 2 shows a conventional superconducting device, and shows a wiring diagram when there are two superconducting coils. Figure 3 shows the current A and magnetic field T when the example shown in Figure 1 was demonstrated using a small superconducting coil.
FIG. 4 shows another embodiment of the present invention, and is a wiring diagram for a case where there are four superconducting coils and two permanent switches. 1~1''...Superconducting coil, 2~2-''...Tip of lead wire of superconducting coil, 3~3-'...Gate wire, 4,4'...Heater, 5,5'...Permanent switch , 6~6″...excitation power supply for superconducting coil, 7
~7-...Connection point between superconducting coil and power source, 8
...Motor power supply for permanent switch.

Claims (1)

[Claims] 1. A persistent current switch consisting of a plurality of superconducting coils, a power source connected to each, and a gate wire connected in parallel with the superconducting coils and switched between a normal conductive state and a superconducting state, and the gate wire. In a superconducting device equipped with heating means, a plurality of superconducting devices capable of persistent current excitation share a gate line of the persistent current switch, and each lead wire of the superconducting coil and the lead wire are heated by the gate wire. A superconducting device characterized by connecting means. 2. A persistent current switch consisting of a plurality of superconducting coils each having a power source, a power source connected to each, and a gate wire connected in parallel with the superconducting coils and switched between a normal conducting state and a superconducting state, and heating the gate wire. In the superconducting device, each lead wire of the superconducting coil and the means for heating the lead wire are connected to one gate wire, and each power source of the superconducting coil is connected to a gate wire in such a manner that the polarities of the power supplies are opposite to each other. A superconducting device characterized by being connected. 3. A persistent current switch consisting of a plurality of superconducting coils, a power source connected to each, a gate wire connected in parallel with the superconducting coils and switched between a normal conducting state and a superconducting state, and means for heating the gate wire. In the superconducting device, the persistent current switch shares a gate line, and the plurality of superconducting coils are connected to the gate line so that the algebraic sum of the current values of each superconducting coil is less than or equal to the maximum current value among them. A superconducting device characterized by being connected to. 4. Claims characterized in that the lead wire of each superconducting coil connected to the gate wire and a part of the means for heating the lead wire can be switched between a superconducting state and a normal conducting state at the same time as the gate wire. The superconducting device according to item 3. 5. A heater connected in series with the persistent current switch is installed in the lead wire of the superconducting coil and a part of the means for heating the lead wire, and by turning on and off this heater, the lead wire and the lead wire of the superconducting coil are heated. 5. The superconducting device according to claim 4, wherein a part of the means for heating the lead wire is switched between a superconducting state and a normal conducting state at the same time as the gate wire. 6. A persistent current switch consisting of a plurality of superconducting coils, a power source connected to each, a gate wire connected in parallel with the superconducting coils and switched between a normal conducting state and a superconducting state, and means for heating the gate wire. In the superconducting device, a first persistent current switch is made up of one gate line of the persistent current switch, and a second persistent current switch is made up of two gate lines collectively connected to one end of this gate line. and each lead wire of one of the plurality of superconducting coils and a means for heating the lead wire are gathered together at the other end of the one gate wire, and each lead wire of the other side of the superconducting coil is assembled. and means for heating the lead wires are assembled and connected to the other ends of the two gate wires so that the algebraic sum of the current values of each of the superconducting coils is less than or equal to the maximum current value among them. Features of superconducting equipment. 7. A persistent current switch consisting of a plurality of superconducting coils, a current connected to each, a gate wire connected in parallel with the supercurrent coils and switched between a normal conducting state and a superconducting state, and means for heating the gate wire. In the superconducting device, the current flowing through the gate wire is made smaller than the current flowing through each superconducting coil, and each superconducting coil is wound so that the direction of the generated magnetic field is oriented in a desired direction. A superconducting device.