JP2006228500A - Magnetic field generation method and magnetic field generation apparatus - Google Patents

Abstract

A high magnetic field can be generated even when a gap (gap) is increased, and the strength of the generated magnetic field is improved.
A pair of superconductor arrays 110 and 120 each having a plurality of superconductors having the same size and the same shape arranged in a row are arranged to face each other at a predetermined interval, and a pair of superconductors arranged to face each other. A magnetic field generation method for generating a periodic magnetic field in a gap between conductor arrays, wherein a pair of superconductor arrays is formed in a state where the temperature of the pair of superconductor arrays is maintained at a temperature higher than the superconducting transition temperature. A first step (a) in which a uniform external magnetic field of the same polarity is applied, and the pair of superconductor arrays are cooled, so that the temperature of the pair of superconductor arrays 110 and 120 is lower than the superconducting transition temperature. A second step (b), a third step (c) to stop applying a magnetic field to the pair of superconductor arrays and magnetize the pair of superconductor arrays, and a pair of superconductors A fourth step (d) of applying a magnetic field to the body array with a polarity opposite to the polarity; A.
[Selection] Figure 3

Description

  The present invention relates to a magnetic field generation method and a magnetic field generation device, and more specifically, by arranging a magnet such as a permanent magnet or an electromagnet or a magnetic pole material made of a magnetic material having a high permeability and a high saturation magnetic flux density to face each other. The present invention relates to a magnetic field generation method and a magnetic field generation apparatus that generate a magnetic field in a gap between opposing magnets and magnetic poles of a magnetic pole material.

  Conventionally, a magnetic field is formed in the gap between the opposing magnets and the magnetic poles of the magnetic pole material by arranging the magnetic pole material made of a magnet having a high magnetic permeability and a high saturation magnetic flux density, such as a permanent magnet and an electromagnet, facing each other. There are known magnetic field generators of the type that generate

  By the way, in this type of conventional magnetic field generator, the magnetic field (magnetic flux density) suddenly increases as the gap between the opposing magnetic poles, that is, the magnetic pole interval (hereinafter referred to as “gap” as appropriate) increases. It is known that there is a principle characteristic of decreasing.

  A typical example of the problem resulting from such characteristics can be found in an apparatus called an insertion light source that is used as a synchrotron radiation source for generating radiation as described below (Non-Patent Document 1). reference).

  The insertion light source is a device having a periodic magnetic field structure inserted in a linear space between the deflecting magnets of the storage ring in the accelerator, and the synchrotron radiation from the deflecting magnets when the electron beam passes through. It is a light source device that generates powerful synchrotron radiation of higher quality than light. Such insertion light sources are roughly classified into two types called undulators and wiggras. However, in current synchrotron radiation facilities such as SPring-8 owned by the present applicant, the interference effect of light is used. An undulator that generates high-intensity light is mainly used.

  As described above, a periodic magnetic field structure is formed in the insertion light source. Such a periodic magnetic field structure is formed by the conventional magnetic field generator described above, that is, a magnet such as a permanent magnet or an electromagnet, or a high magnetic permeability. It is constructed using a magnetic field generator of the type that generates a magnetic field in the gap between the opposing magnets and the magnetic poles of the magnetic pole material by arranging the magnetic pole materials made of a magnetic material having a high saturation magnetic flux density property facing each other. Yes.

  That is, in the insertion light source, a periodic magnetic field structure is formed by periodically arranging the magnetic poles facing each other, and a periodic magnetic field is generated by the periodic magnetic field structure thus formed. When light generated from each periodic magnetic field overlaps when electrons move, high-intensity light is obtained.

  Therefore, in such an insertion light source, it is necessary to increase the gap between the opposed magnetic poles in order to pass electrons.

  However, since the conventional magnetic field generator has a characteristic that the magnetic field (magnetic flux density) rapidly decreases as the gap is increased as described above, this determines the upper limit of the magnetic field that can be generated in the insertion light source. There was a problem that it was supposed to be.

In addition, such problems are particularly prominent when the period length of the periodic magnetic field is shortened.
T. T. et al. Hara, T .; Tanaka, H .; Kitamura, T .; Bizen, X. Marechal, T.M. Seike, T .; Kohda and Y.K. Matsuura, “Cryogenic Permanent Magnetic Undurators”, Physical Review ST-AB 7 (2004) 050702.

  The present invention has been made in view of the above-described problems of the prior art, and the object of the present invention is to generate a high magnetic field even when the gap (gap) is increased. It is an object of the present invention to provide a magnetic field generation method and a magnetic field generation apparatus that can improve the strength of a magnetic field to be generated.

  In order to achieve the above object, a magnetic field generation method and a magnetic field generation apparatus according to the present invention apply (apply) a uniform external magnetic field to an array of a pair of superconductors opposed to each other and apply the uniform external field. A superconductor is magnetized by a magnetic field.

  That is, since the superconductor magnetized by the uniform external magnetic field described above acts as a permanent magnet, it can generate a periodic magnetic field reflecting the structure of the superconductor array. is there.

  Here, when the critical current density of the superconductor is sufficiently large, the amplitude of the periodic magnetic field generated reflecting the structure of the superconductor array should be higher than that of the rare earth permanent magnet. Is possible, and in principle there is no upper limit.

  Therefore, according to the magnetic field generation method and the magnetic field generation apparatus of the present invention, it is possible to generate a high magnetic field even when the magnetic pole interval is increased, and it is possible to improve the strength of the generated magnetic field.

  In the magnetic field generation method and the magnetic field generation apparatus according to the present invention, for example, bulk high-temperature superconductors may be arranged in a row in order to form an array of opposed superconductors.

  Such a magnetic field generating method and magnetic field generating apparatus according to the present invention can be used for generating a magnetic field in an insertion light source such as an undulator or a wiggler.

Hereinafter, the principle of the magnetic field generation method and the magnetic field generation apparatus according to the present invention will be described in detail with reference to the drawings.

  First, as shown in FIG. 1, a plurality of superconductors 12 having the same dimensions and the same shape arranged in a row (hereinafter referred to as “a plurality of superconductors having the same size and the same shape arranged in a row”). (Referred to as “superconductor arrangement” where appropriate).

  More specifically, the superconductor array 10 shown in FIG. 1 has nine superconductors 12 having a rectangular parallelepiped shape of the same size and shape arranged in a row adjacent to each other on the same plane. is there.

Note that the length of one side of the cuboid-shaped superconductor 12 in the traveling direction of the electron beam is λ _u (λ _u is the period of the magnetic field), and one side of the cuboid-shaped superconductor 12 in the traveling direction of the electron beam. The length (width of each permanent current loop) is W, and the thickness of the rectangular parallelepiped superconductor 12 is L. The lengths of superconductors 112 and 122 to be described later are also expressed in the same manner as the superconductor 12 described above.

  Here, if the superconductor 12 is a type II superconductor, it can be magnetized by applying a uniform external magnetic field. Such magnetization of the superconductor 12 is performed, for example, by applying an external magnetic field in a state where the superconductor 12 is maintained at a temperature higher than the superconducting transition temperature Tc and then cooling to a temperature equal to or lower than the superconducting transition temperature Tc. Can be achieved.

  Thus, when the superconductor 12 is magnetized, a permanent current loop is generated inside each superconductor 12.

  The magnetic field formed by the permanent current loop train generated in each superconductor 12 is a uniform magnetic field having a polarity determined by the permanent current loop (magnetic field offset) and the dimensions of the superconductor 12. A periodic magnetic field reflecting the shape and number, that is, a periodic magnetic field reflecting the periodic structure of the superconductor array 10 is formed.

  Accordingly, by removing the magnetic field offset in the superconductor array 10, a periodic magnetic field reflecting the periodic structure of the remaining superconductor array 10 can be obtained. It can be applied to magnetic field generation in an insertion light source such as an undulator or wiggler.

  The present invention provides a method of magnetizing a superconductor array as described above and a method of removing a magnetic field offset, and can generate a periodic magnetic field in the gap between the opposing superconductor arrays. Provided are a magnetic field generation method and a magnetic field generation apparatus.

That is, the invention according to claim 1 of the present invention is arranged such that a plurality of superconductors having the same size and the same shape are arranged in a row and arranged facing each other at a predetermined interval. A method of generating a periodic magnetic field in a gap between superconductor arrays arranged in a superconducting arrangement, wherein a uniform external magnetic field is applied to the superconductor array, whereby the superconductor array And the magnetic field offset is removed from the magnetized superconductor array by adjusting the external magnetic field.

  Further, in the invention according to claim 2 of the present invention, a pair of superconductor arrays in which a plurality of superconductors having the same dimensions and the same shape are arranged in a row are arranged to face each other with a predetermined interval therebetween, A magnetic field generation method for generating a periodic magnetic field in a gap between a pair of superconductor arrays arranged opposite to each other, wherein the temperature of the pair of superconductor arrays is maintained at a temperature higher than a superconducting transition temperature. In the state, a first step of applying a uniform external magnetic field of the same polarity to the pair of superconductor arrays, and cooling the pair of superconductor arrays, the temperature of the pair of superconductor arrays A second step of lowering the superconductor transition temperature below, a third step of stopping applying a magnetic field to the pair of superconductor arrays, and magnetizing the pair of superconductor arrays, Apply a magnetic field to a pair of superconductor arrays with a polarity opposite to the above polarity Is obtained by way has 4 and steps.

  Further, in the invention according to claim 3 of the present invention, a pair of superconductor arrays in which a plurality of superconductors having the same dimensions and the same shape are arranged in a row are arranged to face each other with a predetermined interval therebetween, A magnetic field generation method for generating a periodic magnetic field in a gap between a pair of superconductor arrays arranged opposite to each other, wherein the gap between the pair of superconductor arrays is opened to a predetermined size, and A first step of applying uniform external magnetic fields of opposite polarities to the pair of superconductor arrays in a state in which the temperature of the pair of superconductor arrays is maintained at a temperature higher than the superconducting transition temperature; A second step of cooling the superconductor arrangement of the pair to lower the temperature of the pair of superconductor arrays below the superconducting transition temperature, and stopping applying a magnetic field to the pair of superconductor arrays And a third step of magnetizing the pair of superconductor arrays In which the way.

  According to a fourth aspect of the present invention, the fifth aspect of the present invention is the fifth aspect of the present invention, wherein the gap between the pair of superconductor arrays is further closed to a predetermined size. It is made to have these steps.

  The invention according to claim 5 of the present invention is the invention according to any one of claims 3 or 4 of the present invention, wherein the pair of superconductor arrays are arranged such that the pair of superconductors face each other. The body is arranged so as to be shifted by half a cycle.

  The invention described in claim 6 of the present invention is the magnetic field generation method according to any one of claims 1, 2, 3, 4 or 5 of the present invention, wherein the superconductor is bulk. Type high temperature superconductor.

  Further, in the invention according to claim 7 of the present invention, a pair of superconductor arrays in which a plurality of superconductors having the same size and the same shape are arranged in a row are arranged to face each other with a predetermined interval therebetween, A magnetic field generation method for generating a periodic magnetic field in a gap between a pair of superconductor arrays disposed opposite to each other, wherein the first magnetic field is disposed so as to surround one outer periphery of the pair of superconductor arrays. A coil and a second coil arranged so as to surround the other outer periphery of the pair of superconductor arrays, and excite the first coil and the second coil to excite the pair of superconductors. A uniform external magnetic field is applied to each conductor array.

  According to an eighth aspect of the present invention, in the seventh aspect of the present invention, the first coil and the second coil are excited with the same polarity. Is.

  In the invention according to claim 9 of the present invention, in the invention according to claim 7 of the present invention, the pair of superconductor arrangements is such that the superconductors facing each other are shifted by a half cycle. The first coil and the second coil are excited with opposite polarities.

  The invention described in claim 9 of the present invention is the invention described in any one of claims 7, 8 or 9 of the present invention, wherein the superconductor is a bulk type high-temperature superconductor. It is what you have.

  Since the present invention is configured as described above, it is possible to generate a high magnetic field even when the magnetic pole interval is increased, and to improve the strength of the generated magnetic field and the magnetic field generation method. There is an excellent effect that the generator can be provided.

  Hereinafter, an example of an embodiment of a magnetic field generation method and a magnetic field generation apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a perspective view of a conceptual configuration of a magnetic field generator according to an example of an embodiment of the present invention.

  This magnetic field generation apparatus 100 includes a first superconductor array 110 in which a plurality of superconductors 112 having the same size and shape of a rectangular parallelepiped shape are sequentially arranged in a row on the same plane, and a superconductor. A plurality of superconductors 122 having a rectangular parallelepiped shape having the same dimensions and the same shape as 112 and a second superconductor array 120 arranged in a row adjacent to each other on the same plane and facing each other with a gap g therebetween. A pair of superconductor arrays arranged in the same manner. The electron beam passes through the gap g between the first superconductor array 110 and the second superconductor array 120.

  A pair of superconductor arrays of the first superconductor array 110 and the second superconductor array 120 are disposed in the gap width variable drive mechanism 130, respectively. By moving in the A direction, the size of the gap g can be arbitrarily changed.

  Further, the magnetic field generator 100 surrounds the first uniform magnetic field generating coil 150 disposed so as to surround the outer periphery of the first superconductor array 110 and the outer periphery of the second superconductor array 120. A pair of uniform magnetic field generating coils is provided, the second uniform magnetic field generating coil 152 being arranged in such a manner.

  Furthermore, the magnetic field generator 100 is provided with a cooling device 140 for cooling the first superconductor array 110 and the second superconductor array 120, respectively.

  Note that the superconductors 112 and 122 can be formed of, for example, a bulk type high temperature superconductor.

Here, as a technique for magnetization of a pair of superconductor arrays composed of the first superconductor array 110 and the second superconductor array 120 described above and a technique for removing a magnetic field offset, the following two methods are used. There is a technique.

  That is, the first technique is arranged so as to surround the outer periphery of the first uniform magnetic field generating coil 150 and the second superconductor array 120 arranged so as to surround the outer periphery of the first superconductor array 110. In this method, only the second uniform magnetic field generating coil 152 is used. On the other hand, the second method is a method using the first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil 152 and the opening / closing motion of the gap g for magnetization.

  Hereinafter, the first method and the second method will be described in detail.

(1) First Method FIGS. 3A, 3B, 3C, and 3D show a pair of the first superconductor array 110 and the second superconductor array 120 according to the first method. The explanatory diagram of the processing procedure of the method of magnetization of the superconductor array of and the method of removing the magnetic field offset is shown.

  First, in the initial state, the temperature T of the pair of first superconductor array 110 and second superconductor array 120 is maintained at a temperature higher than the superconducting transition temperature Tc. The first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil 152 are excited with the same polarity, and are uniformly distributed in the first superconductor array 110 and the second superconductor array 120. An external magnetic field is applied (applied) (FIG. 3A).

  Thereafter, the first superconductor array 110 and the second superconductor array 120 are cooled, and their temperature T is set lower than the superconducting transition temperature Tc (FIG. 3B).

  After this, the excitation of the first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil 152 is cut off, and the first superconductor array 110 and the second superconductor array 120 are connected to each other. When the application of such an external magnetic field is stopped, the first superconductor array 110 and the second superconductor array 110 and the second superconductor array 120 are held in order to keep the magnetic flux inside the first superconductor array 110 and the second superconductor array 120. The superconductor array 120 is magnetized (FIG. 3C), and the magnetized first superconductor array 110 and the second superconductor array 120 generate a periodic magnetic field to which a magnetic field offset is added. To do.

  Finally, by exciting the first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil 152 to the opposite polarity to the first, the first superconductor array 110 and the second supermagnetic field array The conductor array 120 is subjected to a uniform external magnetic field having a polarity opposite to that of the first to remove the magnetic field offset (FIG. 3D).

  By the processing procedure as described above, a periodic magnetic field can be generated in the gap g between the first superconductor array 110 and the second superconductor array 120 that are arranged to face each other.

In the first method, the first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil are used in order to satisfactorily perform the step of removing the magnetic field offset shown in FIG. The uniform external magnetic field initially generated by 152 is so high that the current density of the magnetized first superconductor array 110 and second superconductor array 120 reaches the critical current density j _c. It is preferable.

(2) Second Method FIGS. 4A, 4B, 4C, and 4D show a pair of the first superconductor array 110 and the second superconductor array 120 according to the second method. The explanatory diagram of the processing procedure of the method of magnetization of the superconductor array of and the method of removing the magnetic field offset is shown.

  When this second method is used, the first superconductor array 110 located on the upper side and the second superconductor array 120 located on the lower side are super-aligned along the traveling direction of the electron beam. The conductors 112 and 122 are arranged so as to be shifted from each other by a distance of λu / 2 (half cycle), which is half the length in the traveling direction of the electron beam. That is, the first superconductor array 110 located on the upper side and the second superconductor array 120 located on the lower side are formed by a half cycle between the superconductor 112 and the superconductor 122 located at positions facing each other. They are shifted by a minute.

  First, in the initial state, the gap g between the first superconductor array 110 and the second superconductor array 120 is opened to a predetermined size, for example, maximum (g = maximum value). ). Then, the temperature T of the first superconductor array 110 and the second superconductor array 120 is kept higher than the superconducting transition temperature Tc, and the first uniform magnetic field generating coil 150 and the second uniform The magnetic field generating coil 152 is excited with opposite polarities (FIG. 4A).

  In this way, the gap g is sufficiently opened, and the first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil 152 are excited with opposite polarities, so that a magnetic field is applied to the center of the gap g. Although not provided, the first superconductor array 110 and the second superconductor array 120 can be magnetized. That is, the first superconductor array 110 and the second superconductor array 120 are arranged far away from the center of the gap g, while the first superconductor array 110 is the first superconductor array 110. This is because the second superconductor array 120 is close to the second uniform magnetic field generating coil 152 and is close to the uniform magnetic field generating coil 150.

  Next, the first superconductor array 110 and the second superconductor array 120 are cooled, and their temperature T is set lower than the superconducting transition temperature Tc (FIG. 4B).

  After this, the excitation of the first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil 152 is cut off, and the first superconductor array 110 and the second superconductor array 120 are connected to each other. When the application of the external magnetic field is stopped, the upper first superconductor array 110 and the lower superconductor array 110 and the lower superconductor array 110 are held in order to keep the magnetic flux inside the first superconductor array 110 and the second superconductor array 120. The second superconductor array 120 on the side is magnetized, but its polarity is reversed, so that the magnetic field offset is canceled at the center of the gap g (where the electron beam passes), and the first superconductor array 120 Since the conductor array 110 and the second superconductor array 120 are shifted by λu / 2, a periodic magnetic field without a magnetic field offset is formed (FIG. 4C).

When the gap g is closed to a predetermined size, for example, the minimum value, the magnetic fields generated by the first superconductor array 110 and the second superconductor array 120 facing each other are opposite in polarity. The permanent current is increased in an attempt to suppress the entry of the magnetic fluxes of the other party, and the magnetic field is further enhanced. This increase in the permanent current continues until the critical current density j _c of the first superconductor array 110 and the second superconductor array 120 is reached or the gap g reaches a minimum value (FIG. 4D). ).

  By the processing procedure as described above, a periodic magnetic field can be generated in the gap g between the first superconductor array 110 and the second superconductor array 120 that are arranged to face each other.

Here, the process of magnetization during the change of the gap g in the second method will be examined. In order to simplify the explanation and facilitate understanding, as shown in FIG. The permanent current loops that respectively flow through the conductor array 110 and the lower second superconductor array 120 will be generally described as two long current loops arranged on the upper side and the lower side.

  Due to symmetry, the currents I flowing in the first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil 152, which are two long coils, are the same except for polarity. The self-inductance and the mutual inductance of the first uniform magnetic field generating coil 150 and the second uniform magnetic field generating coil 152, which are two long coils, are referred to as a self-inductance L and a mutual inductance M, respectively. The mutual inductance M and current I are functions of the gap g.

Here, when the value of the gap g is changed from g ₁ to g ₂ , the following formula for indicating a change in magnetic flux is used.

In this equation, the left side and the right side indicate magnetic flux changes caused by self-inductance and mutual inductance, respectively. Therefore, the current change is given by the following equation.

Here, when g ₂ approaches 0, M (g ₂ ) approaches L. In this way, significant enhancement of the permanent current flowing through the first superconductor array 110 and the second superconductor array 120, that is, the magnetic field is expected.

Next, in order to examine the performance of the magnetic field generator shown in FIG. 2, the first superconductor array 110 and the second superconductor array 120 which are arranged to face each other with a gap g therebetween are generated. Calculate the magnetic field.

  In order to simplify the magnetic field calculation, it is assumed that the width (w) of the current loop is infinitely long. In such a case, the magnetic field can be calculated under a two-dimensional approximation, as derived from the following “Explanation for Deriving Equations”.

[Explanation for formula derivation]
Here, a case where a magnetic field generated by an infinitely long coil regularly arranged as shown in FIG. 6 is calculated will be described.

First, considering the case where the current I in the coil is constant in a → 0 and b → 0, the current density distribution in such a coil is expressed as follows.

The magnetic field generated in the yz plane is expressed as follows by the two-dimensional form of Bio Savart's law.

In addition, μ ₀ in the formula (A.1) is a vacuum magnetic permeability.

Since j (ξ) is periodic along the z-axis, it can be expanded into a Fourier series by k _u = 2π / λ _u .

Substituting equation (A.2) in Equation (A.1), it is possible to obtain a vertical magnetic field b _y generated by the infinitely fine coil.

Here, considering the case where a and b have finite values, the magnetic field in such a case is calculated by integrating equation (A.3) for the cross section of the coil.

Substituting equation (A.3) into the above equation and assuming y <g / 2 yields the following equation:

The magnetic field is composed of odd harmonics. Among them, it is most prevalent basic components (n = 0), and has a peak magnetic field B _p on the axis (y = 0).

  Its exponential dependence on the gap is the same as that of an undulator with a rare earth permanent magnet with a Halbach structure (end of [explanation for derivation of equations]).

Here, substituting the equation (A.5) the dimensions shown in FIG. 1, and if 2πL / λμ»1, it is possible to obtain the peak magnetic field B _p achievable in a magnetic field generating apparatus shown in FIG.

Note that j _{c in} Equation 3 is the critical current density of the first superconductor array 110 and the second superconductor array 120.

In practical units,

It becomes.

For example, if λ _u = 15 mm, j _c = ² kA / mm ² , g = 3 mm, a peak magnetic field of about 4T is obtained, which is an insertion with a rare earth permanent magnet with an additional magnetic field of 1.4T About 3 times higher than the light source.

Next, an experiment related to the present invention conducted by the present inventor will be described. That is, the inventor of the present application conducted an experiment using a bulk type high-temperature superconductor prepared from a commercially available material, Gd—Ba—Cu—O (T _{c to} 92 K), in order to demonstrate the effects of the present invention. It was.

  7A, 7B, and 7C show a schematic configuration of the magnetic field generator according to the present invention used in this experiment. 7A is a schematic configuration explanatory diagram of the entire apparatus, FIG. 7B is a schematic configuration explanatory diagram of a superconductor arrangement, and FIG. 7C is a diagram illustrating a superconductor arrangement, a copper holder, It is schematic structure explanatory drawing which shows the relationship with a hall probe.

In this magnetic field generator, a plurality of rectangular parallelepiped bulk type high temperature superconductors 202 having a length corresponding to an undulator period λ _{u of} 10 mm are arranged to constitute a superconductor array 200, and the superconductor array is formed. 200 is fixed to the copper holder 210. The dimensions of the bulk type high temperature superconductor 202 are as shown in FIG.

  The superconductor array 200 fixed to the copper holder 210 is disposed so as to be inserted into the gap G of the electromagnet (normal conduction) 220.

  On the other hand, the copper holder 210 to which the superconductor array 200 is fixed is connected to the head of the cryocooler 230.

  A cartridge type heater 240 is mounted on the copper plate 210, and the temperature of the copper holder 210 is controlled by the cartridge type heater 240.

  Here, the magnetic field of the superconductor array 200 was measured by inserting a hole probe 260 fixed to the cantilever 250 so as to be adjacent to the superconductor array 200. The cantilever 250 is connected to the linear stage 270, and by driving the linear stage 270, the hole probe 260 can be scanned along the z-axis direction. Thereby, the distribution of the magnetic field along the z-axis can be measured.

  In this experiment, the distance from the center of the Hall probe 260 to the surface of the superconductor array 200 was 1 mm. The temperature of the superconductor array 200 was measured with a platinum resistance thermometer attached to them.

  In the experiment, when the effect caused by the iron yoke of the electromagnet 220 was estimated by calculation, it was found that the effect can be ignored because the size of the superconductor array 200 is small.

  As the first experiment, the intrinsic performance of the bulk type high temperature superconductor 202 constituting the superconductor array 200 used in the experiment was measured. In this measurement, one bulk type high temperature superconductor 202 is fixed to a copper holder 210, and a magnetic field generated by one bulk type high temperature superconductor 202 is scanned with a coil current of an electromagnet 220 while performing a Hall probe. This was done by measuring by 260.

The critical current density j _c was determined by comparing with a calculation result of a magnetic field generated by a coil having the same dimensions as the bulk type high temperature superconductor 202.

FIG. 8 shows a graph of measurement results of the above-described experiment. In the graph of FIG. 8, the horizontal axis represents temperature (K), the vertical axis represents critical current density (A / mm ² ), and the critical current density of the bulk type high-temperature superconductor 202 as a function of temperature. j _c is shown.

In this experiment, it was not possible to determine the critical current density j _c at temperatures below 43K. This is because the magnetization of the bulk type high temperature superconductor 202 was not saturated even when the maximum magnetic field supplied by the electromagnet 220 was applied.

Here, the curve shown in FIG.

Is calculated using The above equation is an empirical equation that empirically indicates the relationship between the critical current density j _c and the temperature T.

Using the least squares method, j _c (0) and m have been determined to be 2760 A / mm ² and 2.25, respectively. With these parameters, it can be expected that the critical current density j _{c of} the bulk type high-temperature superconductor 202 reaches 2170 A / mm ² at a temperature of 30K.

After the critical current density j _c of the bulk type high temperature superconductor 202 is measured as described above, as shown in FIG. 7A, the super bulky high temperature superconductors 202 arranged in a line are arranged. A conductor array 200 was constructed, and the magnetic field of the superconductor array 200 was measured.

In order to simulate the method of magnetization of the superconductor array and the method of removing the magnetic field offset, the following steps 1 to 5 are performed.
Step 1: Set temperature of superconductor array 200 to 100 K Step 2: Operate electromagnet 220 to apply 2T Step 3: Cool superconductor array 200 to target temperature Step 4: Magnetic field of electromagnet 220 (B _e ) The magnetic field distribution was measured by decreasing the value by 0.2 T. Step 5: Step 4 was repeated until the magnetic field (B _e ) of the electromagnet 220 reached −2.0 T.

FIG. 9 shows a magnetic field distribution (B _z ) in the z direction measured at a temperature of 59K. In the graph of FIG. 9, the horizontal axis indicates the position (mm) in the z direction, and the vertical axis indicates the magnetic field (T), and each of the electromagnets 220 is measured at a temperature of 59 K at different magnetic fields (B _e ). Magnetic field distribution is shown.

  According to the experimental results shown in the graph of FIG. 9, it can be seen that a typical periodic magnetic field is generated.

As the magnetic field (B _e ) of the electromagnet 220 decreased, the magnetic field amplitude increased, whereas the magnetic field offset decreased. Then, after the magnetic field (B _e ) of the electromagnet 220 reached 0.2T, the increase in the amplitude stopped. This indicates that the magnetization of the superconductor array 200 is saturated.

Therefore, when this superconductor array 200 is operated by the “first method” described above, the magnetic field offset can be eliminated by setting the magnetic field B _e to −0.5 T.

The field amplitude _{B a} and the magnetic field offset _{B o} of the peak-to-peak in the second period (peak-to-peak),

It is defined as

10 (a) is a graph showing the magnetic field amplitude B _a in the second period as a function of the magnetic field B _e at different temperatures T, taking a magnetic field B _{e (T)} on the horizontal axis, the magnetic field the vertical axis the amplitude B _a (T) is taken. Further, FIG. 10 (b) is a graph showing the magnetic field offset B _o in the second period as a function of the magnetic field B _e at different temperatures T, the horizontal axis represents the magnetic field B _{e (T),} the magnetic field the vertical axis The offset B _o (T) is taken.

As shown in FIG. 10A, a higher magnetic field _Be is required for saturation of the magnetic field amplitude Ba at _a low temperature. In particular, 2T | B _e | is not sufficient for saturation at 50K. By applying a higher magnetic field B _e, it can be expected a larger field amplitude B _a, for the capacity of the electromagnet 220 is not sufficient, this experiment was not performed.

Further, from FIG. 10 (b), the regard to the removal of the magnetic field offset, can be found an optimum value of the magnetic field B _e at each temperature.

Further, the inventor of the present application uses the magnetic field in the case of operating by the above-described “second method” by shifting and subtracting two identical data measured as described above by a distance ± λ _u / 4. The distribution was simulated.

11 is the simulation result is shown and illustrates a simulation result in different values of the magnetic field B _e, respectively. Note that for each pair of superconductor arrays facing each other, the period λ _u = 10 mm and the gap g = 2 mm.

  From FIG. 11, it can be seen that the magnetic field offset is removed, resulting in a typical periodic magnetic field distribution between a pair of opposing superconductor arrays with a period of 10 mm.

As described above, according to the present invention, a bulk type high temperature superconductor can be used, and according to this bulk type high temperature superconductor, it is driven by a superconducting coil operating near liquid helium temperature. A much higher operating temperature is tolerated than the insertion light source.

For example, the critical current density j _c of the Gd—Ba—Cu—O superconductor used in the above experiments has been found to be 1.76 kA / mm ² at a temperature of 40 K, which has a period length of 15 mm. Means that a peak magnetic field of 3.59 T can be expected at a gap of 3 mm. This value is about 2.7 times higher than that achieved in undulators with rare earth permanent magnets.

In the above-described embodiment, the case where the present invention is applied to the short-period undulator has been described in mind. However, the present invention can also be applied to wiggler configurations that have a very strong peak magnetic field with a much shorter period length than those of wigglers driven by superconducting coils. Of course. For example, a superconducting magnet having a peak magnetic field of 17 T at a temperature of 29 K has been developed. It has a cylindrical shape with a diameter of 26.5 mm and a thickness of 15 mm. By using this type of superconducting magnet, a wiggler having a peak magnetic field of 10 T or more and a cycle length of less than 30 mm is formed. Is possible. Moreover, since the number of periods can be increased by decreasing the period length, synchrotron radiation with higher luminance can be obtained as a result.

  The present invention can be used for a synchrotron radiation source such as an undulator or wiggler that can be used as an insertion light source for generation of synchrotron radiation, and an electron beam is used as a light source using a beam line using synchrotron radiation. It is used in the field of synchrotron radiation science.

FIG. 1 is a configuration explanatory diagram showing a superconductor arrangement in which a plurality of superconductors having the same size and shape are arranged in a line. FIG. 2 is a perspective view of a conceptual configuration of a magnetic field generator according to an example of an embodiment of the present invention. FIGS. 3A, 3B, 3C and 3D show the attachment of a pair of superconductor arrays comprising a first superconductor array and a second superconductor array according to the first method of the present invention. It is explanatory drawing of the process sequence of the method of a magnetic method, and the method of removal of a magnetic field offset. 4 (a), (b), (c) and (d) show the attachment of a pair of superconductor arrays comprising a first superconductor array and a second superconductor array according to the second method of the present invention. It is explanatory drawing of the process sequence of the method of a magnetic method, and the method of removal of a magnetic field offset. FIG. 5 is an explanatory diagram for explaining the operation of the present invention. FIG. 6 is an explanatory view showing infinitely long coils arranged regularly. FIGS. 7A, 7B, and 7C are schematic configuration explanatory diagrams of the magnetic field generator according to the present invention used in the experiment by the present inventors, and FIG. 7A is a schematic configuration explanatory diagram of the entire device. FIG. 7B is a schematic configuration explanatory diagram of the superconductor array, and FIG. 7C is a schematic configuration explanatory diagram showing the relationship between the superconductor array, the copper holder, and the hole probe. FIG. 8 is a graph showing the experimental results of an experiment by the present inventor. FIG. 9 is a graph showing an experimental result of an experiment by the present inventor. FIG. 10 is a graph showing an experimental result of an experiment by the inventor of the present application. FIG. 11 is a graph showing the result of a simulation performed using the experimental result of the experiment by the present inventor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Superconductor arrangement | sequence 12 Superconductor 100 Magnetic field generator 110 1st superconductor arrangement | sequence 112 Superconductor 120 2nd superconductor arrangement | sequence 122 Superconductor 130 Gap width variable drive mechanism 140 Cooling device 150 1st Uniform magnetic field generating coil 152 Second uniform magnetic field generating coil 200 Superconductor array 202 Bulk type high temperature superconductor 210 Copper holder 220 Electromagnet 230 Cryocooler 240 Cartridge type heater 250 Cantilever 260 Hall probe 270 Linear stage

Claims (10)

Superconductor arrays in which a plurality of superconductors having the same dimensions and the same shape are arranged in a row are arranged to face each other at a predetermined interval, and are periodically formed in the gaps between the superconductor arrays arranged to face each other. A magnetic field generation method for generating a magnetic field,
Magnetizing the superconductor array by applying a uniform external magnetic field to the superconductor array;
A magnetic field generation method characterized by removing a magnetic field offset from the magnetized superconductor array by adjusting an external magnetic field. A pair of superconductor arrays in which a plurality of superconductors having the same dimensions and the same shape are arranged in a row are arranged to face each other at a predetermined interval, and between the pair of superconductor arrays arranged to face each other. A magnetic field generation method for generating a periodic magnetic field in a gap,
Applying a uniform external magnetic field of the same polarity to the pair of superconductor arrays in a state where the temperature of the pair of superconductor arrays is maintained at a temperature higher than the superconducting transition temperature;
A second step of cooling the pair of superconductor arrays to lower the temperature of the pair of superconductor arrays below a superconducting transition temperature;
Stopping applying the magnetic field to the pair of superconductor arrays and magnetizing the pair of superconductor arrays;
And a fourth step of applying a magnetic field having a polarity opposite to the polarity to the pair of superconductor arrays. A pair of superconductor arrays in which a plurality of superconductors having the same dimensions and the same shape are arranged in a row are arranged to face each other at a predetermined interval, and between the pair of superconductor arrays arranged to face each other. A magnetic field generation method for generating a periodic magnetic field in a gap,
In the state where the gap between the pair of superconductor arrays is opened to a predetermined size and the temperature of the pair of superconductor arrays is maintained at a temperature higher than the superconducting transition temperature, the pair of superconductor arrays A first step of applying uniform external magnetic fields of opposite polarities to each other;
A second step of cooling the pair of superconductor arrays to lower the temperature of the pair of superconductor arrays below a superconducting transition temperature;
And a third step of stopping the application of a magnetic field to the pair of superconductor arrays and magnetizing the pair of superconductor arrays. The magnetic field generation method according to claim 3, further comprising:
And a fifth step of closing the gap between the pair of superconductor arrays to a predetermined size. In the magnetic field generation method according to any one of claims 3 and 4,
The pair of superconductor arrays are arranged such that the superconductors facing each other are shifted by a half period. In the magnetic field generation method according to any one of claims 1, 2, 3, 4 or 5.
The superconductor is a bulk type high temperature superconductor. A pair of superconductor arrays in which a plurality of superconductors having the same dimensions and the same shape are arranged in a row are arranged to face each other at a predetermined interval, and between the pair of superconductor arrays arranged to face each other. A magnetic field generation method for generating a periodic magnetic field in a gap,
A first coil disposed so as to surround one outer periphery of the pair of superconductor arrays;
A second coil disposed so as to surround the other outer periphery of the pair of superconductor arrays,
A magnetic field generator characterized by exciting the first coil and the second coil to apply a uniform external magnetic field to the pair of superconductor arrays. The magnetic field generator according to claim 7,
The magnetic field generator characterized in that the first coil and the second coil are excited with the same polarity. The magnetic field generator according to claim 7,
The pair of superconductor arrays are arranged such that the superconductors facing each other are shifted by a half cycle,
The magnetic field generator characterized in that the first coil and the second coil are excited with opposite polarities. The magnetic field generator according to any one of claims 7, 8 or 9,
The superconductor is a bulk type high temperature superconductor.

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