WO2006095614A1

WO2006095614A1 - Superconducting magnet excitation method and superconducting magnet device

Info

Publication number: WO2006095614A1
Application number: PCT/JP2006/303839
Authority: WO
Inventors: Teruo Matsushita; Edmund Soji Otabe; Masaru Kiuchi; Nobuyoshi Sakamoto; Tadahiro Akune
Original assignee: Kyushu Institute Of Technology; Nakamura Sangyo Gakuen
Priority date: 2005-03-08
Filing date: 2006-03-01
Publication date: 2006-09-14
Also published as: JP4201286B2; JPWO2006095614A1

Abstract

It is possible to provide a method for easily preventing or suppressing a magnetic flux creep phenomenon of a superconducting magnet and to provide a superconducting magnet device having such an effect. When exciting a superconducting magnet, the magnetic flux distribution in the superconducting magnet is deformed in advance into such a shape that the magnetic flux creep is substantially not caused. Thus, the superconducting magnet excitation method and device control a magnetic field outside the superconducting magnet. More specifically, for example, when the superconducting magnet is formed by a bias magnet as an external layer and a magnet as an internal layer, initial oscillation current is applied to the magnet of the internal layer while a magnetic field is applied to the external magnet. Next, the current is set to a predetermined value or a magnetic field higher than a predetermined magnetic field is applied to the magnet of the external layer when current is applied to the magnet of the internal layer. Next, the magnetic field of the magnet of the external layer is set to a predetermined magnetic field.

Description

Specification

Method of exciting superconducting magnet and superconducting magnet apparatus

Technical field

The present invention relates to a method of exciting a superconducting magnet, and more particularly to an exciting method for preventing or suppressing a magnetic flux creep phenomenon, and a superconducting magnet apparatus having such an effect. Background art

A superconductor has the property of becoming a superconducting state with zero electrical resistance when it is cooled below its critical temperature. Therefore, if a wire is made using a superconductor and a coil is made using this wire, a superconducting magnet (electromagnet) can be made with very low loss below the critical temperature. Since this superconducting magnet has zero resistance, it is characterized in that there is no Joule loss during current conduction, no heat generation, and a high magnetic field can be generated. If a device called a permanent current switch is attached to this superconducting magnet and the current that flows is made a closed circuit of the superconducting, even if the power of the superconducting magnet is disconnected, the current continues to flow without decreasing, so a constant magnetic field can be generated. A permanent current mode superconducting magnet is formed which can be applied for a long time. When the power supply is connected, the magnetic field changes due to a change in the power supply current, so the accuracy of the magnetic field of the superconducting magnet is not necessarily good, but when it shifts to permanent current mode, the stability of the magnetic field is greatly improved It is characterized by

As described above, in the permanent current mode, a stable high magnetic field can be maintained for a long time. Therefore, it is used for the purpose of applying a constant magnetic field in fields where high stability magnetic fields are required, such as MRI (magnetic resonance imaging) and NMR (nuclear magnetic resonance) used in CT scans. There is. In a powerful device, when the magnetic field fluctuates, the resonance frequency is different, and as a result, the image is disturbed or an incorrect measurement is performed, so a particularly stable magnetic field is required.

By the way, even if the superconducting magnet is operated in the permanent current mode to obtain a constant magnetic field for a long time, the magnetic field is gradually reduced because the permanent current is actually alleviated by the magnetic flux creep phenomenon. . This flux creep phenomenon is explained as follows.

[0005] The fact that the superconductor has zero resistance means that the flux does not enter the superconductor strictly. State only, which is realized only at low magnetic fields. On the other hand, in a high magnetic field, the magnetic flux enters the superconductor and is in a mixed state. The invading magnetic flux is trapped by impurities in the superconductor called a pinning center and becomes immobile. This force that captures magnetic flux is called a pinker. Lorentz force, ie (magnitude of the magnetic field) x (magnitude of current density) is less than pin force, sometimes the flux line is trapped at the pinning center and the flux does not move, so the resistance is zero . Therefore, in this state, the superconductor does not generate resistance and does not lose current for the current density up to the critical current density (maximum current per unit area that can flow to a certain superconductor). The critical current density has the property of being proportional to the pin force.

[0006] If magnetic flux continues to be trapped at the pinning center at a current density below the critical current density, it becomes a permanent current. However, under finite temperature, it is probable that the trapped magnetic flux moves out of the pinning center force. This is the flux creep phenomenon. When a magnetic flux creep phenomenon occurs, the magnetic flux lines change further into the external force superconductor or, depending on conditions, move out little by little, resulting in a change in the magnetic field. Therefore, the flux creep phenomenon can not maintain a constant magnetic field. In this way, the magnetic field is relaxed by the flux creep phenomenon. Such magnetic flux creep phenomenon becomes noticeable when the temperature and the magnetic field are high. The high temperature oxide superconductors that are attracting attention recently have a problem of flux creep compared to the conventional metallic superconductors used at extremely low temperatures due to the high service temperature. Therefore, some means of suppressing the flux creep phenomenon is needed.

[0007] Conventionally, generally, when such a magnetic flux creep phenomenon occurs and the magnetic field decreases, the permanent current mode is released, the power is reconnected, and the magnetic field is applied again. It was done. Other methods have been proposed to reduce or suppress the flux creep phenomenon. For example, in Japanese Patent Application Laid-Open No. 11-164820 (Patent Document 1), a compensation coil corresponding to a superconducting coil is used, and the magnetic flux of the magnetic field is compensated by Methods have been proposed to prevent attenuation. In addition, attempts have been made to stabilize the permanent current by adjusting the temperature of the superconductor (Patent Document 2). However, these methods have the disadvantage that the device is complicated.

Patent Document 1: Japanese Patent Application Laid-Open No. 11-1 164820

Patent Document 2: U.S. Pat. No. 5,270,291

Corrected paper (rule 3⁄4) Disclosure of the invention

Problem that invention tries to solve

The object of the present invention is to provide a method for effectively and easily preventing or suppressing the magnetic flux creep phenomenon by changing the magnetic flux distribution inside the superconducting magnet in the superconducting magnet. Another object of the present invention is to provide a superconducting magnet device having such an effect.

Means to solve the problem

Among the present inventions, according to claim 1 of the present invention, in exciting the superconducting magnet, in order to previously change the magnetic flux distribution inside the superconducting magnet into a form in which magnetic flux creep is unlikely to occur, the outside of the superconducting magnet It is a method of exciting a superconducting magnet characterized by controlling the magnetic field of

Among the present inventions, according to claim 2 of the present invention, the superconducting magnet is composed of a bias magnet in the outer layer and a magnet in the inner layer. It is an excitation method.

Among the present inventions, the invention according to claim 3 is characterized in that an oscillating current which vibrates up and down with respect to a predetermined current value is supplied to the superconducting magnet, and is set to a predetermined current value next time. It is an excitation method of the superconducting magnet according to claim 1 or 2.

Among the present inventions, the invention according to claim 4 is characterized in that, in a state where a magnetic field is applied to the bias magnet in the outer layer, an oscillating current is first applied to the magnet in the inner layer, and then a predetermined current value is set. It is an excitation method of the superconducting magnet according to claim 2.

According to a fifth aspect of the present invention, in the state where a magnetic field higher than a predetermined magnetic field is applied to the bias magnet in the outer layer, current is supplied to the magnet in the inner layer and then the magnetic field of the bias magnet in the outer layer. 3. The method of exciting a superconducting magnet according to claim 2, wherein the magnetic field is set to a predetermined magnetic field.

[0014] The invention described in claim 6 of the present invention is a superconducting magnet apparatus, characterized in that a means for controlling the magnetic field outside the superconducting magnet is provided.

According to a seventh aspect of the present invention, in the superconducting magnet according to the seventh aspect of the present invention, the bias magnet for the outer layer is used. 7. A superconductive magnet apparatus according to claim 6, wherein said superconductive magnet apparatus comprises:

Among the present inventions, the invention according to claim 8 is a means capable of supplying an oscillating current oscillating up and down with respect to a predetermined current value to means for controlling a magnetic field in a superconducting magnet. 7 is the superconducting magnet device according to 7 above.

Among the present inventions, the invention according to claim 9 is a means for controlling the magnetic field, a means capable of applying a magnetic field to the bias magnet in the outer layer, and a means capable of flowing current or oscillating current to the magnet in the inner layer. It is a superconducting magnet device according to claim 7.

The invention according to claim 10 of the present invention is a superconducting magnet apparatus according to any one of claims 6 to 9, characterized in that a means for heating the superconducting magnet is provided. .

Effect of the invention

According to the present invention, for example, the prevention or suppression of the magnetic flux creep phenomenon of the superconducting magnet is achieved by a very simple procedure such as first flowing oscillating current which vibrates up and down, and then setting the current value to a predetermined value. can do. Therefore, the phenomenon that the magnetic field of the superconducting magnet is relaxed due to the magnetic flux creep can be prevented or suppressed, and as a result, the magnetic field of the superconducting magnet can be stably maintained constant. According to the present invention, the effect of suppressing the flux creep phenomenon is extremely high. For example, conventionally, the normal operation of the superconducting magnet in the permanent current mode can be performed only for 10 days. The extension will be easily realized.

Brief description of the drawings

FIG. 1 is a view showing how a superconducting magnet is operated in a permanent current mode by a permanent current switch.

FIG. 2 is a view showing how the magnet of the inner layer is excited by the current vibration method.

FIG. 3 is a view for explaining the relationship between magnetic flux distribution and magnetic flux creep in the current vibration method.

FIG. 4 is a view for explaining the relationship between magnetic flux distribution and magnetic flux in the current vibration method.

FIG. 5 is a diagram showing an example of measuring a time change of magnetic flux in an example of high magnetic field excitation method. FIG. 6 is a view showing an example of the time change (relaxation) of the magnetic flux of the sample in the example of the high temperature excitation method. BEST MODE FOR CARRYING OUT THE INVENTION

According to the knowledge of the inventor of the present invention, in the superconducting magnet, a method (high temperature excitation method) of exciting at a high temperature is used as a method of preventing or suppressing the flux creep phenomenon by changing the magnetic flux distribution inside the superconducting magnet. is there. That is, the superconducting magnet is excited by applying a current at a temperature higher than a predetermined temperature, and then the superconducting magnet is shifted to a permanent current mode, and then the superconducting magnet is adjusted to a predetermined temperature. In this method, first, the superconducting magnet is set to a temperature slightly higher than a predetermined temperature at which normal operation is performed, and current is supplied to excite the current. After that, it shifts to the permanent current mode and lowers the temperature to a predetermined temperature.

The high temperature excitation method will be described with reference to the drawings. FIG. 1 is a diagram showing the operation of the superconducting magnet in the permanent current mode with the permanent current switch. Fig. 1 (a) shows a state in which the superconducting magnet is directly excited by an external DC power supply. Fig. 1 (b) shows a state where the permanent magnet switch is disconnected from the power supply by switching the permanent current switch, and a constant magnetic field is applied by the permanent current. Attenuation is very small because superconducting magnets have zero resistance. Also, because the power supply is disconnected, the stability is very high.

In the superconducting magnet, first, in the state of FIG. 1A, the temperature of a low temperature region cooled by a refrigerant such as liquid helium or liquid nitrogen is set to a predetermined temperature, ie, a predetermined operation temperature of the superconducting magnet. At a higher temperature, the current is energized to excite. Next, the excited superconducting magnet is transferred to the permanent current mode shown in FIG. 1 (b), and then the superconducting magnet is cooled and adjusted to a predetermined operating temperature. The degree of raising the temperature higher than the predetermined temperature is not particularly limited, but at most about 20 K is sufficient. The higher the degree, the larger the heat loss in order to adjust the cooling temperature to a predetermined temperature, which is not preferable, and the effect of suppressing the flux creep is not sufficient below 1 K. The means of temperature control 'is not particularly limited, and the temperature in the low temperature region can be adjusted by a known method and apparatus.

As a structure of the superconducting magnet, typically, it is simply one superconducting magnet. There are some that are configured, and some that are configured with an outer layer bias magnet disposed outside and an inner layer magnet inserted inside thereof. The magnet of the latter structure is a form frequently used in NMR etc. as a structure for obtaining a high magnetic field. The high temperature excitation method can be applied to the superconducting magnet of any of the above configurations.

The principle of the high temperature excitation method is considered to be as follows. At high temperatures, the pinning center has a remarkable magnetic flux creep phenomenon in which the force for capturing the magnetic flux inside the superconductor weakens, and the movement of the magnetic flux is large. In that state, current is first applied, a magnetic field is applied, and magnetic flux creep allows movement of the magnetic flux to some extent, thereby relaxing the magnetic field to some extent. After that, when the temperature is lowered, it is considered that the pinning center is now intensified in the ability to capture the magnetic flux, and the magnetic flux tends to stay in the superconductor. Therefore, the magnetic flux is strongly captured by the pinning center and the magnetic flux creep phenomenon is extremely weak, as compared with the simple application of the magnetic field. This method is effective for superconducting magnets of either structure, using one superconducting magnet or superconducting magnet nets in the outer and inner layers.

In the case of NMR magnets, the inner layer magnet is often made of a high temperature superconductor in order to generate a high magnetic field. In this case, the outer layer magnet is made of a conventional metallic superconductor in order to make it inexpensive. For this reason, the operating temperature may be 4.2 K at normal pressure liquid helium temperature or superfluid liquid helium near 2 K under reduced pressure. As described above, when the operating temperature is 4.2 K or less, when first cooling to the normal pressure liquid helium temperature 4.2 K, the current is applied for excitation (high temperature excitation), and then the pressure is reduced. Cooling to around 2 K enables high-temperature excitation to be realized. In this case no special equipment is required.

The inventors of the present invention have conducted research on another viewpoint as a method of preventing or suppressing the magnetic flux creep phenomenon by changing the magnetic flux distribution inside the superconducting magnet by using the superconducting magnet, and the present invention is achieved. It is Among the present inventions, according to the first aspect of the present invention, in exciting the superconducting magnet, in order to previously change the magnetic flux distribution inside the superconducting magnet to a form in which magnetic flux creep is less likely to occur, The method of exciting a superconducting magnet characterized in that the magnetic field of the above is controlled. In addition, Satoshi Inogami, whose magnetic field outside the superconducting magnet was controlled 1 There are no particular limitations on the method and means used, and conditions such as current and magnetic field can be varied and controlled.

[0028] The invention according to claim 2 limits the superconducting magnet to a superconducting magnet composed of an outer layer bias magnet disposed outside and an inner layer magnet inserted inside the magnet. A magnet with a structure of force is suitable for obtaining a high magnetic field.

In the present invention, in order to change in advance the magnetic flux distribution inside the superconducting magnet to a form in which magnetic flux creep is unlikely to occur, a preferred example of the method of controlling the magnetic field outside the superconducting magnet will be described below. This will be described specifically.

[0030] The invention of claim 3 is characterized in that a vibration current which vibrates up and down with respect to a predetermined current value is supplied to the superconducting magnet, and the current is set to a predetermined current value in the following manner. Method (current oscillation method). And this method is also applicable to both the one constituted simply by one superconducting magnet and the one constituted by the bias magnet of the outer layer disposed outside and the inner layer magnet inserted inside thereof. Possible Forces In particular, as described in claim 4, the present invention can be suitably applied to a superconducting magnet composed of an outer layer bias magnet and an inner layer magnet inserted therein. And in that case, in the state where the magnetic field is applied to the negative magnet of the outer layer, an oscillating current is first applied to the magnet of the inner layer, and then the superconducting magnet is excited by setting to a predetermined current value. Do.

The principle of this method will be described with reference to the drawings. FIG. 2 is a diagram showing how the magnet of the inner layer is excited by the current oscillation method. Fig. 2 (a) shows the situation when a current (I) is supplied to the superconducting magnet in the inner layer while the magnetic field is applied by the bias magnet in the outer layer. The current is made to flow up to a predetermined current value, ie, a current higher than the target current value of the superconducting magnet, and then it is repeatedly lowered and raised again, that is, the oscillating current is supplied to gradually increase the target current. Indicates the status to be set to the value. When the current is changed as shown in FIG. 2 (a), a magnetic field is applied to the coil. At this time, the magnetic flux distribution of the magnetic flux density (B) inside the superconducting magnet is shown by the solid line in FIG. It is thought that In Fig. 2 (b), d indicates the distance to the center inside the superconductor. If this is affected by the flux creep phenomenon, the expected flux distribution as shown by the dotted line in (b) of Fig. 2 is the average of this And the solid line in Fig. 2 (b), it is almost the same as the distribution before the flux creep phenomenon, so the externally generated magnetic field is almost the same. Ultimately, the internal magnetic flux distribution has a jagged pattern, which is more susceptible to magnetic flux creep than when the current is simply increased to generate a magnetic field.

The invention according to claim 5 of the present invention relates to a superconducting magnet including a bias magnet in the outer layer and a magnet in the inner layer, and a state in which a magnetic field higher than a predetermined magnetic field is imprinted on the bias magnet in the outer layer. In the method of exciting a superconducting magnet, a current is supplied to the magnet in the inner layer to generate a magnetic field, and then the magnetic field of the bias magnet in the outer layer is set to a predetermined magnetic field, ie, a target magnetic field. Excitation method).

The principle of this method is considered as follows. In general, the critical current density decreases monotonically with the increase of the magnetic field. Therefore, when the magnet in the inner layer is excited with a high magnetic field, the critical current density may be reduced by flowing current. By demagnetizing the bias magnet in the outer layer, the critical current density in the magnet in the inner layer is increased (the pin force is also increased), so that the magnetic flux invading the inside of the superconductor can be stopped by the stronger pin force. It becomes difficult to move, resulting in weakening of the flux creep phenomenon.

[0034] The invention according to claim 6 of the present invention is a superconducting magnet apparatus characterized in that the superconducting magnet apparatus is provided with means for controlling the magnetic field outside the superconducting magnet. The means for controlling the magnetic field is not particularly limited. The invention according to claim 7 limits the superconducting magnet to one composed of the bias magnet in the outer layer and the magnet in the inner layer.

[0035] The invention according to claim 8 employs, as a means for controlling the magnetic field, a means capable of flowing an oscillating current which vibrates up and down with respect to a predetermined current value to the superconducting magnet. The invention according to claim 9 is a superconducting magnet apparatus employing, as means for controlling a magnetic field, means capable of applying a magnetic field to a bias magnet in the outer layer, and means capable of flowing current or oscillating current into a magnet in the inner layer. The invention according to claim 10 is a superconducting magnet apparatus provided with means for heating the superconducting magnet in addition to the means for controlling the magnetic field.

So far, various superconducting magnet devices and their application devices have been developed. In these superconducting magnet devices, basically, the coil is wound in a state where a superconducting coil portion cooled to a very low temperature, a means for supplying a current from an external excitation power supply thereto, and a required magnetic field are generated. It consists of a superconducting switch that shorts the beginning and end of the winding (see Figure 1). The invention according to claims 6 to 10 is that in the superconducting magnet device under force, means for controlling the magnetic field outside the superconducting magnet is provided as an accessory device. The various means can be any known or commercially available device that does not need to be special.

At present, superconducting magnets are most often used for medical MRI magnets.

Since these are metal-based superconductors, the operating temperature is low and the influence of flux creep S is small. Even so, it is a reality that some auxiliary devices are combined to prevent the relaxation of the magnetic field. Therefore, by incorporating the method and Z or device of the present invention, it is not necessary to combine several accessory devices, and a stable magnetic field can be obtained inexpensively.

[0038] An NMR magnet of over 20 T, which is used for structural analysis of proteins, etc., uses a magnet using a high-temperature oxide superconductor in the center to realize a high magnetic field. The reason is that the high-temperature oxide superconductor can maintain the superconductivity even under a higher magnetic field than the metal-based superconductor. However, due to the use of a high temperature oxide superconductor, the flux creep phenomenon in the high temperature oxide superconductor has determined the performance of the entire system. Thus, the method and apparatus Z or apparatus of the present invention can be used in such a field.

Also, in the near future, when a superconducting magnet using high temperature oxide superconductor is to be produced in earnest, the magnetic flux creep phenomenon becomes a serious problem, and the method and Z or the device of the present invention are in various fields. Will be used by Hereinafter, the present invention will be described in detail by way of examples. Example

[Example 1] (Example of current oscillation method)

The experiment was conducted using a superconducting magnet consisting of an outer layer bias magnet and an inner layer magnet. While the magnetic field was applied by the bias magnet in the outer layer, current (I) was passed through the superconducting magnet in the inner layer while changing the current as shown in (a) of FIG. The current The current is increased to a current higher than a predetermined current value (the target current value of the superconducting magnet), and then it is repeatedly set to the target current value by repeating the lowering and raising again, that is, flowing the oscillating current. . At this time, the magnetic flux density at the cross section of the superconducting magnet is as shown by the solid line in (b) of FIG. Ultimately, the internal magnetic flux density distribution has a jagged pattern, which makes it less susceptible to flux creep than when simply increasing the current to generate a magnetic field.

This is illustrated in FIG. In FIG. 3, (1) (2) (3) (4) shows the internal magnetic flux distribution at each time 1, 2, 3 and 4 when the current shown in FIG. 2 (a) is increased or decreased. In the region up to the center of the superconductor. In (1), the force immediately after the increase has a constant slope inside. This slope is proportional to the critical current density. As time passes, the distribution of dotted lines shifts to the distribution of solid lines. This is the force by which magnetic flux penetrates from the outside due to magnetic flux creep. Alternatively, it may be said that the critical current density has decreased. As a result, the internal magnetization greatly changes, and the magnetic field changes outside.

On the other hand, (2) and (3) are passed to (4). When the current is increased or decreased, the magnetic flux can be moved in and out only from the surface of the superconductor, so the history remains and the distribution is finally as shown in (4). In this case, even if the magnetic flux distribution changes due to the magnetic flux creep, the overall average magnetization does not change, and as a result, the external magnetic field hardly changes.

Actually, the magnetization is a magnetic flux distribution (1) (2) (3) (4), that is, the force at which the time changes at times 2, 3 and 4 and the result of the numerical simulation It is shown in FIG. As will be understood from this, the absolute value of the magnetic field 規格 M standardized by the final saturation value M of the magnetization is at time 1, 2

0

Changes significantly with time, but it hardly changes at time 4. After 100 seconds, it settles almost constant at time 4.

Second Embodiment Example of High Magnetic Field Excitation

An external magnetic field of 0.6 T is applied to the outer layer bias magnet (Y-based oxide superconductor) of the superconducting magnet composed of the outer layer bias magnet and the inner layer magnet, and current is supplied to the inner layer magnet. Then, an example of measuring the time change of the magnetic field of the inner layer magnet by setting the external magnetic field to 0.58 T is shown in FIG. It can be seen that the time change of the magnetic flux is very small. On the other hand, when the external magnetic field is measured at a constant 0.6 T, the magnetization is single. It turns out that it is increasing to the key. Therefore, it was possible to confirm that the flux magnetic phenomenon can be suppressed by setting the magnetic field to a high value.

Reference Example (Example of High-Temperature Excitation Method)

The temperature of the Y-based oxide superconductor is raised by a temperature range of 60 K to a temperature range of ΔΤ, a current is applied there to apply a magnetic field of 0.6 T (high temperature excitation), and then it is cooled to 60 K The time change (relaxation) of the magnetic field of the sample was examined. The results are shown in FIG. As shown in FIG. 6, when ΔΤ is OK, the magnetic flux changes with time and the absolute value decreases. That is, at first there is a gradient of the magnetic flux distribution and the absolute value of the magnetic flux is large, but since there is a magnetic flux creep phenomenon, the magnetic flux exceeds the pin force by the pinning center from time to time with the outside. Since the gradient of the magnetic flux distribution becomes smaller, the absolute value of the magnetic flux becomes smaller.

However, when ΔΤ is large, the change of the magnetic field with respect to time becomes extremely small. For example, when a current is applied at a high temperature such as 7K to LOK and a magnetic field is applied, almost no change in magnetic field is observed. This is because the absolute value of the magnetic flux that the pin force is small at high temperatures is also small, but by cooling to the specified temperature, the pin force is increased, and the magnetic flux invading the inside of the superconductor is strongly pinned. Because it is stopped, it is because the flux line has become a movement.

Industrial applicability

According to the present invention, the phenomenon that the magnetic field of the superconducting magnet is relaxed due to the magnetic flux creep can be prevented or suppressed, and as a result, the magnetic field of the superconducting magnet can be stably maintained constant. . And, according to the present invention, according to the present invention, the method of preventing magnetic field relaxation has a large effect of preventing magnetic field relaxation, as compared with the complicated apparatus and method used in the conventional methods of preventing the magnetic flux creep. It can be obtained, and it can be readily incorporated into current devices which may or may not require additional equipment. And the effect is that the relaxation time can be extended to about 10 times that of the conventional one, and the influence on the industry is very large. For example, MRI (magnetic resonance imaging) or N MR (nuclear magnetic resonance) used in CT scan It is expected that one step use in the field of resonance).

Claims

The scope of the claims

[1] A superconducting magnet characterized by controlling an external magnetic field of the superconducting magnet in order to change the magnetic flux distribution inside the superconducting magnet to a form in which magnetic flux creep hardly occurs when exciting the superconducting magnet. How to excite the magnet.

[2] The method for exciting a superconducting magnet according to claim 1, wherein the superconducting magnet is composed of a bias magnet in the outer layer and a magnet in the inner layer.

[3] The method of exciting a superconducting magnet according to claim 1 or 2, characterized in that an oscillating current oscillating up and down with respect to a predetermined current value is supplied to the superconducting magnet and then set to a predetermined current value. .

[4] The superconductivity according to claim 2, characterized in that, in a state where a magnetic field is applied to the bias magnet of the outer layer, an initial vibration current is supplied to the magnet of the inner layer and the current value is set to a predetermined current value. How to excite the magnet.

[5] While applying a magnetic field higher than a predetermined magnetic field to the bias magnet in the outer layer, a current is supplied to the magnet in the inner layer, and then the magnetic field of the bias magnet in the outer layer is set to a predetermined magnetic field. An excitation method of the superconducting magnet according to Item 2.

[6] A superconducting magnet apparatus comprising: means for controlling a magnetic field outside the superconducting magnet.

[7] The superconducting magnet apparatus according to claim 6, wherein the superconducting magnet is composed of an outer layer bias magnet and an inner layer magnet.

[8] The superconducting magnet device according to claim 6 or 7, wherein the means for controlling the magnetic field is a means capable of passing an oscillating current oscillating up and down with respect to a predetermined current value to the superconducting magnet.

[9] A means for controlling a magnetic field A means capable of applying a magnetic field to a bias magnet in the outer layer, and a means capable of flowing current or oscillating current into the magnet in the inner layer.

[10] The superconducting magnet apparatus according to any one of claims 6 to 9, further comprising means for heating the superconducting magnet.