JP2003031399A - Permanent magnet embedded type high magnetic field generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high magnetic field generating device increasing magnetic field intensity while keeping the accuracy of magnetic field distribution which was impossible in a superconductive transmission line magnet or a conventional electromagnet. SOLUTION: A permanent magnet is inserted into the cavity of the superconductive transmission line magnet or the conventional electromagnet. The magnetic field intensity of the cavity magnetic field between the magnetic poles of the permanent magnet is increased close to four teslas without further saturating iron.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention of this application relates to a permanent magnet built-in type high magnetic field generator. More specifically, the invention of this application includes high energy physics, nuclear physics, energy science, material / material science, life science,
In a circular charged particle accelerator such as a synchrotron, cyclotron, storage ring (storage ring), which can be used for medical application research, forms a high-intensity magnetic field necessary for deflecting, converging and diverging charged particles. The present invention relates to a high magnetic field generator incorporating a magnet.

[0002]

2. Description of the Related Art Up to now, in the research and development of circular charged particle accelerators such as a synchrotron, a cyclotron, and a storage ring (accelerator science), the energy or number of charged particles to be accelerated or stored has been used. Research objectives have been placed in the direction of increasing. In particular, in colliders, efforts have been made to increase the collision frequency (luminosity) of charged particles.

In order to increase the acceleration energy of the charged particles, it is necessary to increase the size of the accelerator and increase the magnetic field strength of the magnet for deflecting and converging / diverging the charged particles. Superconducting electromagnet technology was introduced to increase the magnetic field strength, but it did not reach the level required in fields such as high-energy physics and nuclear physics, and the size of the accelerator only increased. Finally, a huge circular accelerator with a circumference of several tens of kilometers was developed.

In the United States, the hadron collider SSC (Superconduct), which is a circular collider, is used.
ing Super Collider) was discontinued by the Ministry of Energy in the middle of implementation of the plan, reflecting the increase in its scale and budget. As a result, in the research and development of high energy accelerators in the United States, a new circular hadron collider, which is smaller in size than the linear colliders and SSCs, which are colliding linear accelerators, has become the mainstream, followed by circular lepton colliders. One muon collider has listed it as the main accelerator in the development plan.

On the other hand, in Europe, the circular accelerator LHC (Large Hadron C) is considered to be the last hadron collider.
The construction of a muon collider is being considered as a lepton collider, as in the United States.

As described above, the center of research and development of high-energy hadron colliders in the next generation is shifting from the United States to Europe, and the American high-energy physics community is feeling a sense of crisis. Under such circumstances, in the United States, a very large accelerator VLHC (Very Large Had
ron Collider) plans are being proposed.

On the other hand, the present inventors have developed a high magnetic field permanent magnet from the viewpoint of miniaturizing the circular accelerator (a high magnetic field circular charged particle accelerator using a permanent magnet (Kumada et al., Japanese Patent Application No. 2000-301078)). , Magnetic field generator (Kumada et al., Japanese Patent Application No. 2001-086098)). However, since the high magnetic field obtained by these inventions is used as a direct current magnetic field, a small cyclotron or FFAG is used as a particle accelerator.
(Fixed Field Alternating Gradient) It cannot be denied that it was used only for accelerators and the like.

By the way, at the VLHC research and development site as the latest cutting edge of magnet technology, Fermilab (Fermi National Accelerator Laboratory) is mainly used.
Superconducting Transmission Line Magnet / Pipet, which is an extremely simplified structure of the magnet used in
ron) is being researched and developed.

The structure of this magnet is such that a superconducting cable is made into a pipe shape to conduct electricity, an iron core is covered from above and below in the upper and lower directions of the pipe, and gaps of dipole magnetic fields in opposite directions are provided between the iron cores. It is to make two. As an accelerator, protons are rotated in opposite directions to collide with each other in the voids of the magnets arranged on the circumference, and the perimeter reaches 240 km. The most important feature of this magnet is its low price because of its simple structure. It is said that the superconducting electromagnet alone has a space factor of 95% and is converted into Japanese yen of just over 240 billion yen.

On the contrary, the most dissatisfied point is that the magnetic field strength cannot exceed 2 Tesla even if it is done excessively. This is because the saturation of iron causes the magnetic field distribution to change as the excitation of the magnetic field increases, and it becomes impossible to maintain the highly accurate spatial distribution of the magnetic field, which is particularly required for the storage ring. Currently, it is not possible to exceed this 2 Tesla wall.

Therefore, in the VLHC plan, there is no choice but to divide the plan into two phases, and after the 2 Tesla magnet, there is a plan to put a high field magnet of 9.8 Tesla in the same tunnel as the second phase plan. However, at 2 Tesla, SSC (Superconducting Supe), which had been frustrated in the middle of the plan before.
There is also criticism that it does not look different from r Cllider) 2
There is a strong demand for magnets that exceed Tesla.
This is the first problem to be solved by the present invention.

[0012] Further, if the above can be realized, there is a possibility to open the way to miniaturization of the high energy advanced accelerator and the medical accelerator synchrotron. The small synchrotron with a deflection magnetic field strength of 3 Tesla has a new utility value together with the high magnetic field permanent magnet FFAG, and will have a great impact on the spread of medical and therapeutic accelerators. This is the second problem to be solved by the present invention.

Therefore, the invention of this application has been made in view of the above circumstances, and in order to solve the problems of the prior art and to deflect, converge and diverge charged particles in a circular charged particle accelerator. It is an object of the present invention to provide a high magnetic field generator with a built-in permanent magnet that forms a high-strength magnetic field required for the above.

[0014]

SUMMARY OF THE INVENTION The invention of this application is to solve the above-mentioned problems. First, a permanent magnet having an air gap between magnetic poles is used without using an iron core and an iron yoke. And a permanent magnet while being placed in an external magnetic field by a superconducting electromagnet using at least one of an iron yoke and an iron yoke, while maintaining a high magnetic field spatial distribution required for accelerator performance without saturating at least one of an iron core and an iron yoke. There is provided a high magnetic field generation device characterized in that the magnetic field strength in the air gap provided in is the magnetic field strength of a synthetic magnetic field of a magnetic field of a permanent magnet and an external magnetic field of a superconducting electromagnet.

Secondly, in the first invention, there is provided a high magnetic field generator characterized in that the magnetic field strength of the synthetic magnetic field is 2 tesla or more. Thirdly, a permanent magnet having an air gap between magnetic poles without using an iron core and an iron yoke is used to generate a magnetic field by using an ordinary coil made of a material other than a superconducting material and at least one of the iron core and the iron yoke. Placed in the void of the electromagnet to be generated, while maintaining the high magnetic field spatial distribution required for the performance of the accelerator without saturating at least one of the iron core and the iron yoke, the magnetic field strength in the void provided in the permanent magnet, Provided is a high magnetic field generation device characterized by having a magnetic field strength of a synthetic magnetic field of a magnetic field of a permanent magnet and a magnetic field of an electromagnet.

A fourth aspect of the present invention provides the high magnetic field generator according to the third aspect of the invention, wherein the magnetic field strength of the synthetic magnetic field is 2 tesla or more. Fifthly, in the third aspect of the present invention, there is also provided a high magnetic field generation device characterized in that the constituent elements of the permanent magnet are small unit magnets that are insulated in order to enable rapid and repetitive operation. provide.

Sixthly, there is also provided a high magnetic field generator according to any one of the first and third inventions, wherein the permanent magnet is made of a rare earth magnet material. Seventhly, in the first or third aspect of the invention, the permanent magnet is cooled at the liquid nitrogen temperature to improve the temperature stability of the magnetic field and also improve the residual magnetic flux density and the coercive force. There is also provided a high magnetic field generator characterized by:

Eighth, in any one of the first to seventh inventions, the combination of the electromagnet and the permanent magnet is a combination in a plane transverse to the beam direction of the accelerator. Also provided is a high magnetic field generator.

Ninth, in any one of the first to eighth inventions, when the charged particles are converged by the synchrotron accelerator, the ratio of the magnetic field gradients of the electromagnet and the permanent magnet becomes equal. A high magnetic field generator is also provided.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the first problem, the magnetic field generator of the invention of this application was invented by Fermilab's Foster (Fermilab report, "Design study").
For a staged VLHC) Fermilab TM-2149, 6/4/01) By combining a superconducting transmission line magnet with a permanent magnet using a rare earth magnet material, it was not possible to develop Foster etc. from 3 Tesla to 4 Tesla. It is intended to realize the magnetic field strength of (1) with a gap magnetic field.

In the case of a 3 Tesla magnet, 1.5 Tesla is made of a superconducting electromagnet, the remaining 1.5 Tesla is made of a permanent magnet, and the magnetic fields of the respective magnets are superposed on the gap provided between the magnetic poles of the permanent magnet. Obtained synthetic magnetic field. The whole superconducting transmission line magnet is about 240 mm x 280 mm, which is considerably larger than the diameter of the superconducting pipe formed by the superconducting cable is about 40 mm, and the size of the beam pipe is about 20 mm x 40 mm. However, since the entire superconducting transmission line magnet is considerably larger than the beam pipe, it can be said that it is an appropriate size for inserting a permanent magnet.

In the space between the two iron cores in the superconducting transmission line magnet, where the beam pipe is inserted,
A permanent magnet produces a magnetic field of 1.5 Tesla. The permanent magnet has a U-shape, a C-shape, an O-shape, etc. having an air gap between the magnetic poles, and the outer diameter thereof may be about 100 mm. By changing the shape of the iron core of the superconducting transmission line magnet, 1
A space of 00 mm is provided for installing the permanent magnet.

The superconducting transmission line magnet creates an external magnetic field of 1.5 Tesla with respect to the permanent magnet, but since its own iron core is outside this external magnetic field, 1.5 Tesla alone is used. The magnetic field inside the iron core of the superconducting transmission line magnet is not stronger than when it is generated. Also, permanent magnets are exposed to a strong external magnetic field of 1.5 Tesla, but it is a problem because rare earth magnet materials with a high coercive force that can withstand an external magnetic field of up to 3 Tesla are available. Is few.

Therefore, in the gap between the magnetic poles of the permanent magnet inserted in the superconducting transmission line magnet, a composite magnetic field of the magnetic field of the permanent magnet and the magnetic field of the superconducting transmission line magnet is obtained.

To be precise, the magnetic field strength of each magnet is set to be 0.1 tesla higher than that of the permanent magnet, and the minimum magnetic field when the superconducting transmission line magnet is AC-excited for the synchrotron mode is, for example, The incident magnetic field is set to 0.1 Tesla (the maximum magnetic field is 3.1 Tesla) so that charged particles having a predetermined energy can be incident. This permanent magnet is installed symmetrically on both sides of the superconducting pipe consisting of a superconducting cable, and the electromagnetic force with the superconducting pipe is also symmetrical, so the electromagnetic force acting on the original superconducting transmission line magnet The advantage of being small is unchanged. Further, since the size of the permanent magnet is considerably smaller than that of the superconducting transmission line magnet, the cost is not increased and the energy can be greatly increased.

Also in solving the second problem, the outer diameter is 10
A 1.5 Tesla permanent magnet of about 0 mm is effective. In a conventional H-type or C-type electromagnet, a gap having a width of <100 mm + width required for magnetic circuit> is provided, and a permanent magnet having a gap between magnetic poles is used as the gap of the electromagnet without using an iron core and an iron yoke. When installed in the center, the magnetic field in the air gap of the permanent magnet becomes a composite magnetic field of the magnetic field of the electromagnet and the magnetic field of the permanent magnet. As in the case of the first problem, the external magnetic field is 1.
Since it is about 5 tesla, the demagnetization effect can be avoided by selecting a permanent magnet material having a high coercive force.

Further, when the permanent magnet is inserted into the space of the superconducting transmission line magnet or the usual electromagnet, the temperature stability of the magnetic field is improved by cooling the permanent magnet at the liquid nitrogen temperature, and the residual magnetic flux density and retention are improved. It is possible to improve the magnetic force as well.

Further, in the case of the superconducting electromagnet, the repetition of the excitation of the magnet is slow, whereas in the conventional electromagnet, the repetition of the excitation can be accelerated. In this case, when solving the second problem, the permanent magnet is composed of the divided small magnets that are small insulated according to the excitation speed.

In any case of the superconducting transmission line magnet / ordinary electromagnet, the point to be particularly noted is that the magnet of the present invention is applied to a circular accelerator such as a synchrotron, so that the magnet of the present invention is a pure magnet. There is no problem when it is used as a deflecting magnet, but in the case where it has a converging action, it is necessary to keep the converging force constant according to the change of the deflection magnetic field strength. For that purpose, it is necessary to make the magnetic field gradient of the permanent magnet equal to the magnetic field gradient of the superconducting transmission line magnet / normal electromagnet.

In either case of the superconducting transmission line magnet / normal electromagnet, the electromagnet and the small permanent magnet are transversal to the traveling direction of the beam of the accelerator.
It is a feature of the present invention that the combination is performed in the plane of (erse direction).

Embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in details.

[0032]

EXAMPLES Example 1 FIG. 1 shows a superconducting transmission line magnet (6) proposed by Fermilab's Foster for VLHC.
FIG. This superconducting transmission line magnet (6)
Can be said to be a super-ferric superconducting magnet in which the copper coil portion of the conventional copper coil electromagnet is replaced with a superconducting coil.

This superconducting transmission line magnet (6) is
A superconducting pipe (2) formed by a superconducting cable is cooled with liquid helium (1), and an iron core (iron yoke) is provided around the vacuum insulating duct (3) outside the superconducting pipe (2).
(5) is covered from above and below, and two beam ducts (4) are provided on both left and right sides of the superconducting pipe (2). Although not shown in this figure, there is actually a return superconducting cable below this section.

The greatest feature of this superconducting transmission line magnet (6) is that the left and right sides of the superconducting pipe (2) formed by the superconducting cable are symmetrical, and electromagnetic force acts on the superconducting pipe (2). Is almost never taken. Therefore, the superconducting cable forming the superconducting pipe (2) does not require a strong structural material for resisting electromagnetic force, so that the cost is overwhelmingly low. According to Foster et al., It would cost 200 million dollars even if the superconducting transmission line magnet (6) was packed to the circumference of an accelerator of 240 km. When converted to Japanese yen, it is 1 million yen / m, which can be said to be an order of magnitude cheaper than a normal conducting magnet.

The broken line in FIG. 2 shows the original position of the iron core (5), and the solid line shows the superposition when the iron core (5) is positioned with the air gap expanded to insert the small permanent magnet. A state of the transmission line magnet (6) is shown.

In FIG. 3, a small C-shaped permanent magnet (7) having a gap between magnetic poles is installed around the beam duct (4), and the beam duct (4) formed by the small permanent magnet (7). The direction (8) of the magnetic field inside is shown.

In FIG. 4, a superconducting transmission line magnet (6)
The state that the small permanent magnet (7) is inserted into the void is shown. The above figures are schematic diagrams although the scale ratios of dimensions are approximately correct. As a rough estimate, a small superconducting transmission line magnet is enough to produce 1.5 Tesla, so the additional cost of the magnet of this invention is almost the same as the original superconducting transmission line magnet developed by Foster. Expected to be the same. <Embodiment 2> FIG. 5 shows a sectional view of an H-type electromagnet (9) using a conventional copper coil. Here, iron core (1
0), the iron yoke (11) and the copper coil (12) constitute an electromagnet, and in the void formed therein, a small permanent magnet (14) having a beam duct (13) is used as a liquid for a cooling duct. It is installed in a nitrogen tank (15) and is filled with liquid nitrogen (16). In this example, the beam duct (13) hits the gap between the magnetic poles of the permanent magnet (14), and the magnetic field in the beam duct (13) is the combined magnetic field of the H-type electromagnet (9) and the permanent magnet (14). Becomes

The permanent magnet (1 in the void of the H-shaped electromagnet (9)
The purpose of cooling 4) and the like with liquid nitrogen (16) is to enhance the temperature stability of the magnetic field for use in the accelerator and to improve the magnetization characteristics at low temperatures. Although not shown in the figure, it is also possible to cool the permanent magnets and the like in the gap with liquid nitrogen in the form of the first embodiment.

While the repetition of excitation is slow in the superconducting electromagnet, the repetition of excitation can be accelerated in the conventional electromagnet. In the second embodiment, depending on the excitation speed,
It is also possible to construct a permanent magnet with small magnets which are small and insulated. When a permanent magnet is placed in an external magnetic field that is changed by an electromagnet, an eddy current flows and is heated or a magnetic field is generated by the eddy current.However, by configuring the permanent magnet with insulating and divided small magnets as described above, these Can be avoided.

In both the first and second embodiments, the electromagnet and the small permanent magnet are combined in a plane lateral to the traveling direction of the beam of the accelerator.

[0041]

As described in detail above, according to the present invention, by combining a superconducting electromagnet and a permanent magnet, it is possible to maintain the high-performance magnetic field distribution and to repeatedly perform the slow excitation of more than 2 Tesla to nearly 4 Tesla. There is provided a high magnetic field generator that enables operation. Similarly, a combination of an electromagnet other than a superconducting electromagnet and a permanent magnet provides a high magnetic field generation device that enables rapid and repetitive operation of excitation.

The magnet combining the superconducting electromagnet and the permanent magnet as described above has a low price medium magnetic field (3 to 4 Tesla), and the problem of iron saturation in the superconducting electromagnet, which was difficult in the low magnetic field (2 Tesla). It is possible to solve the problem of direct current magnetic field, which is often inconvenient with a permanent magnet, and it is possible to eliminate the drawbacks of both.

Similarly, in electromagnets other than superconducting electromagnets, by combining with a small permanent magnet, it is possible to achieve an AC magnetic field range of 3 Tesla, which has been impossible in the past.
It can open the way to application to low-cost small accelerators for medical use.

[Brief description of drawings]

FIG. 1 is a sectional view of a superconducting transmission line magnet used in a high magnetic field generator according to an embodiment of the present invention.

FIG. 2 is a diagram showing a state in which a magnetic pole interval of a superconducting transmission line magnet is widened in order to insert a small permanent magnet in the high magnetic field generator of the same embodiment.

FIG. 3 is a diagram showing an appearance of a small permanent magnet used in the high magnetic field generator of the same embodiment.

FIG. 4 is a view showing a state in which a small permanent magnet is incorporated in a superconducting transmission line magnet in the high magnetic field generator of the same embodiment.

FIG. 5 is a diagram showing a state in which a small permanent magnet is incorporated in a gap of a conventional electromagnet in a high magnetic field generator of another embodiment.

[Explanation of symbols]

1 liquid helium 2 Superconducting pipe 3 vacuum insulation duct 4 beam duct 5 Iron core (iron yoke) 6 Superconducting transmission line magnet 7 Permanent magnet 8 Direction of magnetic field in air gap 9 H type electromagnet 10 iron core 11 iron yoke 12 copper coils 13 beam duct 14 Small permanent magnets 15 Liquid nitrogen tank 16 Liquid nitrogen

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Claims (9)

[Claims] 1. A permanent magnet having an air gap between magnetic poles without using an iron core and an iron yoke is placed in an external magnetic field of a superconducting electromagnet using at least one of the iron core and the iron yoke, While maintaining the high magnetic field spatial distribution required for accelerator performance without saturating at least one,
A high magnetic field generator characterized in that the magnetic field strength in the air gap provided in the permanent magnet is the magnetic field strength of the synthetic magnetic field of the magnetic field of the permanent magnet and the external magnetic field of the superconducting electromagnet. 2. A high magnetic field generating device according to claim 1, wherein a magnetic field strength of the synthetic magnetic field is 2 Tesla or more. 3. A permanent magnet having an air gap between magnetic poles without using an iron core and an iron yoke is used to generate a magnetic field using an ordinary coil made of a material other than a superconducting material and at least one of the iron core and the iron yoke. Placed in the air gap of the electromagnet, the magnetic field strength in the air gap provided in the permanent magnet is maintained while maintaining the high magnetic field spatial distribution required for the performance of the accelerator without saturating at least one of the iron core and the iron yoke. A high magnetic field generator characterized by having a magnetic field strength of a synthetic magnetic field of a magnetic field by the magnetic field and a magnetic field by the electromagnet. 4. A high magnetic field generation device, wherein the magnetic field strength of the synthetic magnetic field according to claim 3 is 2 Tesla or more. 5. The high magnetic field generator according to claim 3, wherein the constituent elements of the permanent magnet are small unit magnets that are insulated so as to enable repeated rapid excitation operation. 6. A high magnetic field generator, wherein the permanent magnet according to claim 1 or 3 is made of a rare earth magnet material. 7. The high magnetic field generation according to claim 1, wherein the permanent magnet is cooled at a liquid nitrogen temperature to improve the temperature stability of the magnetic field and also improve the residual magnetic flux density and the coercive force. apparatus. 8. The high magnetic field generator according to claim 1, wherein the combination of the electromagnet and the permanent magnet is a combination in a plane lateral to the beam direction of the accelerator. 9. The high magnetic field generator according to claim 1, wherein the ratio of the magnetic field gradients of the electromagnet and the permanent magnet are equal when the charged particles are converged by the synchrotron accelerator.