DE102010042598A1 - Superconductive magnetic resonance-magnet arrangement for use in magnetic resonance-magnet system, has slot dividing dual pancake coil into partial coils that are rotated and/or displaced with dual coil to produce spatial field pattern - Google Patents

Abstract

The arrangement has a superconductive-band (1) comprising a slot (2) between ends (3a, 3b) of the superconductive-band, where the slot is formed such that the superconductive-band forms a loop enclosing the slot in a closed manner. The superconductive-band is wound to a dual pancake coil, and the slot divides the dual pancake coil into partial coils. The partial coils are rotated and/or displaced with the dual pancake coil to produce a predetermined spatial field pattern. The superconductive-band comprises a high temperature superconductor material i.e. yttrium barium copper oxide.

Description

Background of the invention

The invention relates to a superconducting MR (Magnetic Resonance) magnet arrangement with a filamentless superconductor tape.

An MR magnet assembly having a filamentless superconductor tape is known Laskaris, ET, Ackermann, T., Dorri, B. Gross, D., Herd, K., Minas, C., A Cryogen-Free Superconducting Magnet for Interventional MRI Applications, IEEE Transactions to Applied Superconductivity, Vol. 5, No , 2, June 1995 ,

Superconducting wires, through which an electric current can flow without loss, are used in a variety of ways, in particular for high-field magnetic coils. Superconductor materials become superconducting only below a material-specific transition temperature T _c , so that they must be cooled for technical use.

For MR applications, it is important to create a temporally constant spatially homogeneous magnetic field. The temporal constancy requires a lossless current flow within the magnetic field generating coil. In order to ensure such a lossless flow of current, it is necessary to connect the superconducting wires extremely low resistance or resistance by means of superconducting wire connections, so-called "joints" in such a way that all connected conductor elements together form a virtually resistance-free closed loop. Wire connections with non-superconducting solder, for example, completely unsuitable. The quality of the superconducting junctions with respect to vanishing electrical resistance is an indispensable prerequisite for the application of a superconducting magnet for MR applications.

Superconducting multifilament wires with filaments of so-called low-temperature superconductor material (LTS conductors), which comprise a plurality of filaments which are embedded in a matrix and are produced by means of drawing processes, have hitherto been used as conductor elements for MR magnet arrangements. The main usable materials for the superconducting filaments are based on the metal alloy NbTi and the intermetallic compound Nb ₃ Sn. The typical operating temperature for these materials is 4.2 K or less. Liquid helium is used for cooling.

Such superconducting conductor elements can be sufficiently low-resistance connected to each other by, for example, uncovered filaments of superconducting wires are connected together with a superconducting solder ...

However, such LTS conductors are superconducting only in magnetic fields with field strengths below about 25T. For this reason, the highest operating field strength achieved with special MR magnets is 23.5 T. If one wants to generate even higher magnetic field strengths with MR magnets, LTC conductors alone are no longer sufficient. In order to produce even higher magnetic field strengths, magnetic arrangements are conceivable which comprise conductor elements based on high-temperature superconductors (HTS conductors). Especially suitable here HTS conductors of the so-called second generation, which are not designed as a multifilament conductor but as a band conductor.

Second-generation HTS strip conductors also achieve higher current densities (more than 1000 A / mm ² at temperatures below 5 K) in magnetic fields above 25 T and are suitable for their material yttrium-barium-copper-oxide (YBCO) and the manufacturing process and the resulting superconducting properties in principle particularly well for high field applications above 25 T. These so-called "coated conductors" (CC) are based on a layered architecture, wherein a superconductor layer is deposited on a metallic carrier tape, for example by means of sputtering, laser ablation, Electron beam evaporation or chemical vacuum deposition. The width of this band conductor is typically in the range between a few mm and a few cm. Such band conductors are for example from the Brochure Bruker HTS YBCO CoatedConductorDataSheet from Bruker HTS GmbH as well as out http://www.bruker-est.com/ybco-tapes.html known.

However, the use of these HTS band conductors in MR magnet arrangements is made more difficult by the fact that, according to the prior art, no methods are known which enable reliable and sufficiently resistance-free wire connections between these conductor elements.

The use of filamentless strip conductors in an MR magnet arrangement is over Laskaris, ET, Ackermann, T., Dorri, B. Gross, D., Herd, K., Minas, C., A Cryogen-Free Superconducting Magnet for Interventional MRI Applications, IEEE Transactions to Applied Superconductivity, Vol. 5, No , 2, June 1995 known. However, these are LTS band conductors, in which methods for producing sufficiently resistance-free wire connections between conductor elements are known.

Because of the costly cooling of LTS materials, however, it is also desirable for MR applications, HTS coils (critical temperature T _c > 40 K), which can be relatively easily and inexpensively cooled by liquid nitrogen. With regard to the use of HTS strip conductors for MR applications, however, the current state of the art fundamentally involves the problem of connecting the filament-free strip conductors with sufficiently low resistance in order to ensure a lossless current flow within the coil consisting of this material. So far, HTS strip conductors are mainly used in power engineering, where it does not depend on a low-resistance connection of the strip conductor.

Object of the invention

It is therefore an object of the invention to provide an MR magnet arrangement which uses filamentless superconductor tapes for magnetic field generation, in which a loss-free current flow through the superconductor tapes and thus a high temporal constancy of the generated magnetic field is realized.

Brief description of the invention

This object is achieved according to the invention in that the superconductor belt has a slot in the longitudinal direction between both ends of the superconductor belt, wherein the slot is designed such that the superconductor belt forms a closed loop enclosing the slot, and in that the superconductor belt Band is wound to at least one double coil, wherein the slit divides the double coil into two sub-coils, wherein at least one double coil, the sub-coils are each rotated against each other and / or shifted, that the sub-coils ( 6a . 6b . 6c . 6d ) generate a given spatial magnetic field profile in a measuring volume.

As a filamentless superconductor tape can, for example, a band-superconductor described above (2nd generation superconductor) are used.

"Slit in the longitudinal direction" hereby means that the slot extends from one end of the superconductor belt to the other end of the superconductor belt, wherein the slit does not have to be rectilinear, but also wave, zigzag, etc. may be formed. The ends of the superconductor tape comprise a non-slotted area. The superconductor tape thus forms a closed loop without having to be connected by means of a joint. The magnet assembly according to the invention therefore has a joint-free superconducting loop, whereby a lossless flow of current is realized within the loop.

To generate the necessary magnetic field strength, the slotted superconductor tape is wound up into a double coil and forms two partial coils.

Due to the joint-free design of the superconductor loop, an application of HTS band conductors in magnetic resonance is made possible.

Preferably, the double coil is a double pancake coil with pancake coils as partial coils. A pancake coil is spirally wound in a plane (flat coil). In general, the double pancake coil is wound on one or more coil carriers (winding carrier). However, there are also other coil forms, for. As solenoid coils, possible.

After winding the superconductor tape into a double pancake coil, the partial magnetic fields generated by the partial coils would largely cancel out. In order nevertheless to generate a magnetic field which can be used for MR measurements, according to the invention the partial coils are rotated and / or displaced relative to one another. In this way, a large number of magnetic field courses can be realized, which are required in MR measurements. Thus, for example, a magnet arrangement according to the invention with only partial coils shifted relative to one another can serve as a shim coil for another magnet arrangement.

In a particularly preferred embodiment of the magnet arrangement according to the invention, in at least one double coil (preferably in all double coils), the partial coils are each rotated and / or shifted in such a way that both partial coils of a double coil in the same direction in current flow within the closed loop be traversed by the stream. "Equilibrium" here means that the amount of the effective magnetic field (caused by superposition of the magnetic fields of the partial coils) in a measuring volume is greater than the magnetic field of the individual partial coils. In the case of double coils, having a coil axis, the measuring volume is preferably located radially inside the double coil. Coils in the same direction in the sense of the invention can be achieved, for example, by turning the coils relative to one another at an angle which is between 90 ° and 270 °.

As a result of the rotation of the partial coils relative to one another, a magnetic field is thus generated in an effective manner. By suitable choice of the distance between the two partial coils to each other, it is possible to achieve a certain homogeneity of the magnetic field in the geometric center of this arrangement.

The ends of the superconductor belt are slightly twisted against each other due to the rotation of the sub-coils, so that in this area small interference fields can arise, which are negligible, however, with a correspondingly high number of turns (order of magnitude 1000 with double pancake coils) of the double coil.

When the superconductor tape is wound into only a single double coil, the sub-coils are connected together across the ends of the tape. Preferably, however, the superconductor tape is wound up into at least two double coils. As a result, the coil assembly formed by the superconductor tape can cover a larger space and, by optimizing the axial positions of the component coils, it becomes possible to generate a large-area homogeneous magnetic field. When using only a double coil, the possibilities for this optimization of the positions for generating a large-scale homogeneous volume are limited accordingly.

Preferably, the double coils are arranged so that the partial coils of all double coils are flowed through in the same direction in the same direction by the current during flow of current within the closed loop. In this way, a particularly high magnetic field can be generated.

In an alternative embodiment, the double coils are arranged such that current flows through at least one double coil in the closed loop in opposite directions with respect to other double coils. Ie. There is at least one adjacent pair of double coils whose magnetic fields partially cancel each other out. Magnetic field gradients can be realized or interference fields shielded by means of the double coils through which they pass in opposite directions.

In a specific embodiment, the double coils have different inner radii and / or different outer radii. Double coils with a larger inner and / or outer radius, for example, as shielding or compensation coils for z. B. double coils with smaller inner radii and / or outer radii serve. It is particularly preferred if all partial coils with a first radius are traversed by current in the same direction, while the partial coils are traversed in opposite directions with a second radius with respect to the partial coils with the first radius. Such magnet arrangements can serve as a main field coil with shielding coil.

Preferably, the partial coils are arranged coaxially with each other. The axis with respect to which the coil sections are arranged coaxially, runs perpendicular to the winding plane of the coil sections. Thus, with a suitable spacing of the partial coils within the double coil, a homogeneous field can be generated.

In a particularly preferred embodiment, the double coils are arranged coaxially with each other. However, there are also applications conceivable in which the double coils can be arranged at an angle to each other, for example, to produce an annular magnetic field.

Due to the high current-carrying capacity of HTS-strip conductors and the fact that low-resistance joints between HTS-strip conductors are not feasible, the advantages of the invention are particularly effective if the superconducting strip comprises HTS material, preferably YBaCuO.

A preferred embodiment provides that the superconductor belt is provided with two power connections for feeding power into the loop, wherein a heatable end of the superconductor belt is located between the power connections. The magnet arrangement can be charged via the power connections. The heatable end of the superconductor tape serves as a superconducting switch. Once the charging process is completed, the heating of the heatable end of the superconductor belt is terminated, so that the superconductor belt again forms a lossless circuit. Such a magnet arrangement can be used as a field coil, for example for an MR apparatus.

It is particularly advantageous if the slot is rectilinear and the slot divides the band in the slotted area (that is, excluding the non-slotted ends) into subbands of the same width. The slot then runs along the longitudinal axis of the superconductor belt. The partial coils wound from these subbands generate magnetic fields of the same strength, so that in particular symmetrical coil arrangements can be easily realized.

The invention also relates to an MR magnet system which comprises at least two magnet arrangements according to the invention and to an MR magnet system which comprises at least one magnet arrangement according to the invention and at least one other magnet arrangement.

Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and those listed further can be used individually or in any combination. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

Drawing and detailed description of the invention

Show it:

1 a schematic representation of a superconductor belt with slot;

2 a schematic representation of a double pancake coil, which consists of the slotted superconductor tape 1 was wound;

3 a schematic representation of an embodiment of the magnet arrangement according to the invention with a double pancake coil, which consists of the slotted superconductor tape 1 was wound, the sub-coils are rotated by 180 ° from each other;

4 a schematic representation of an embodiment of the magnet arrangement according to the invention with a double pancake coil, a superconducting switch and power supply lines;

5 a schematic representation of a double pancake coil pair, which consists of the slotted superconductor tape 1 was wound;

6 a schematic representation of an embodiment of the magnet arrangement according to the invention with the double pancake coil pair, which consists of the slotted superconductor tape 1 was wound, the sub-coils are each a double pancake coil rotated by 180 ° from each other;

7 an embodiment of an MR magnet system according to the invention with a plurality of magnet assemblies according to the invention, whose double pancake coils have different radii, and

8th An embodiment of an MR magnet system according to the invention with a plurality of magnet assemblies according to the invention, whose double pancake coils have different radii and are traversed in the same direction by the current.

The 2 to 8th show the invention using double pancake coils.

1 shows a superconductor band 1 with a slot 2 extending along the longitudinal axis L of the superconductor belt 1 between the two ends 3a . 3b of the superconductor band 1 extends and the superconductor band 1 in two subbands 4a . 4b Splits. The ends 3a . 3b of the superconductor belt each comprise an area which is not slotted and as a connection between the two subbands 4a . 4b serves, leaving the slotted superconductor tape 1 forms a closed loop. In the in 1 the example shown shares the slot 2 the band in the slotted area in two equal width subbands 4a . 4b , In this way, similar partial coils 6a . 6b to be wound ( 2 ). However, it may also be advantageous not to place the slot centrally in the superconductor tape, so that one obtains sub-bands of different widths. The slot 2 runs in the longitudinal direction, ie in the direction of the greater extent of the superconductor belt 1 , However, it is not absolutely necessary that the slot is rectilinear. Also, the slot can 2 in the form of a recess, so that the sum of the widths of the subbands 4a . 4b smaller than the width of the superconducting tape 1 in the unslotted area. It is crucial that by slotting the superconductor tape 1 a closed loop is created. The subbands 4a . 4b So no longer need to be connected by means of a joint.

By winding the in 1 shown slotted superconductor tape 1 creates a double pancake coil 5 ' , as in 2 shown. The subbands 4a . 4b of the superconductor band 1 each form a partial coil 6a . 6b that over the ends 3a . 3b of the superconductor band 1 connected to each other, so that a current flow from the first part coil 6a in the second part coil 6b and from this again in the first part coil 6a is possible. However, the current directions in the two partial coils run 6a . 6b the in 2 shown double pancake coil 5 ' in opposite directions, so that the magnetic fields of the partial coils 6a . 6b (Depending on the distance and angular orientation of the sub-coils to each other) at least partially extinguish. Typically, the superconductor tape including the subbands is coated on all sides with an electrical insulating material. Alternatively or additionally, an electrical insulating film may be wrapped in each partial coil, which separates the windings from each other. Typically, after winding, each sub-coil is mechanically stabilized and fixed in itself, for example by casting with a synthetic resin, whereby each sub-coil becomes a self-supporting structure. Alternatively or additionally, each partial coil may remain on a suitable support body (coil carrier) or be applied to suitable carrier bodies after casting.

In order nevertheless to generate the largest possible effective magnetic field, in the magnet arrangement according to the invention, the partial coils 6a . 6b twisted against each other, so that the two partial coils 6a . 6b In the same direction can be traversed by the stream. The effective (by superposition of the partial coils 6a . 6b generated) magnetic field is then greater than the magnetic field of each partial coil 6a . 6b alone. A maximum effective magnetic field is obtained when the partial coils 6a . 6b around 180 ° twisted against each other, as in 3 shown. Such a double pancake coil 5 already constitutes an MR magnet arrangement according to the invention. The magnet arrangement according to the invention can furthermore comprise one or more coil carriers (not shown) on which / which the double pancake coil 5 is wound up. Be the partial coils 6a . 6b wound on different bobbins, the twisting of the partial coils 6a . 6b against each other by rotating the bobbin and the windings of the sub-coils located thereon 6a . 6b respectively. When using only one coil carrier for both partial coils 6a . 6b , need to twist the sub coils 6a . 6b against each other, the windings of a partial coil 6a . 6b be taken in the meantime from the bobbin.

Each partial coil is wound around an axis a. In the in 3 shown embodiments, both partial coils are aligned coaxially with each other, so that the axes of the partial coils 6a . 6b at the same time the axis of the double pancake coil 5 forms. The sub-coils in the embodiments shown here are in the form of circular rings. However, the invention also includes other shapes, such as elliptical rings or rectangular frames.

The power supply in a magnet arrangement according to the invention with a double pancake coil 5 as they are in 3 is shown, can be done by induction. Is the superconductor band 1 in the superconducting state, there is a lossless current flow through the double pancake coil and thus enables the generation of a stable magnetic field, as is desired for MR applications. For example, the arrangements according to the invention can be operated in this way as shielding coils.

In the event that the power supply should not be via induction, but by means of an external power source, eg. B. for charging a main field coil for generating the B0 field of an MR device, are in the in 4 shown embodiment of the magnet arrangement according to the invention on both sides of one end 3a of the superconductor band 1 power leads 7a . 7b provided that can be connected to an external power source. The one end 3a of the superconductor band 1 is with a superconducting switch 8th , z. B. in the form of a heating loop, provided, whereby the end 3a of the superconductor band 1 can be brought into the normal conducting state and during charging represents an electrical resistance to charging the double pancake coil 5 via the external power source. After completion of the charging process, the superconducting switch switches 8th the superconductor band 1 short again (heating is stopped).

Depending on the length of the superconductor belt 1 and according to the desired number of windings can also be several double pancake coils 5 . 5 ' from a superconductor band 1 be wrapped. 5 shows an example of an arrangement of two double pancake coils 5a ' . 5b ' , their partial coils 6a . 6b respectively. 6c . 6d not twisted against each other. For use as a magnet arrangement according to the invention, the partial coils of each double pancake coil 5 ' be twisted against each other so that the sub-coils 6a . 6b respectively. 6c . 6d within each double pancake coil can be traversed in the same direction from the stream. Be in the in 5 shown arrangement, the left sub-coils 6a . 6c against the respective right part coils 6b . 6d twisted, you get the in 6 shown magnet arrangement according to the invention, in which all partial coils 6a . 6b . 6c . 6d both double pancake coils 5a . 5b in the same direction to be traversed by the stream. On the other hand, if one twists the outer partial coils of both double pancake coils 6a . 6d opposite the inner part coils 6b . 6c , one obtains a magnet arrangement according to the invention (not shown), wherein, although within each double pancake coil 5 the partial coils 6a . 6b in the same direction, the first double pancake coil with respect to the second double pancake coil, however, flows in opposite directions. In this way magnetic fields with magnetic field gradients can be realized. A magnet arrangement then has double pancake coils through which it flows in opposite directions if at least two adjacent double pancake coils are aligned with respect to one another in such a way that the effective field generated in the measurement volume by the superimposing of the magnetic fields of the two adjacent double pancake coils is smaller than the largest field generated by a single of the two double pancake coils. In coaxial arrangements, the measuring volume is located around the area of the axis a of the magnet arrangement. In 6 are the double pancake coils 5 coaxially with each other (ie, the magnet assembly has an axis coincident with the axes of the double pancake coils 5 whereby the generation of a homogeneous magnetic field within the double pancake coils 5 is produced. However, it is also conceivable that the double pancake coils are displaced parallel to one another (axes of the double pancake coils are parallel) or at an angle to one another (axes of the double pancake coils then form an angle of> 0 °). By means of many angularly arranged double pancake coils, the magnetic field lines can, for example, describe a defined arc. In this way, for example, correction coils may be arranged, with the help of which certain desired field shapes are generated and certain deviations of the field form of a magnet arrangement from the desired homogeneous in MR applications homogeneous shape can be corrected.

7 shows a magnetic coil system according to the invention, which comprises a plurality of magnet assemblies according to the invention MA1, MA2, wherein two magnet arrangements MA1 are provided for generating the B0 field, which can be charged in each case via an external current source ( 4 ), as well as two shielding magnet assemblies MA2 without power supply, in which current is induced due to magnetic field changes ( 3 ). The magnet assemblies MA1, MA2 have different radii. The current flow within the magnet arrangements MA2 takes place here in opposite directions with respect to the current flow of the magnet arrangements MA1.

8th also shows a magnet system according to the invention, which comprises a plurality of magnet arrangements MA1, MA3 according to the invention, all magnet arrangements MA1, MA3 being provided for generating the B0 field and each being able to be charged via external current sources ( 4 ).

Instead of in 8th For example, a magnet arrangement of LTS conductors according to the prior art can also be present. Here, the radially outer magnet assembly of LTS conductor can generate a background field with a thickness up to for example 24 T and the radially inner arrangement according to the invention with HTS band conductor MA1 an additional field of, for example, 10 T, the entire magnet assembly thus a magnetic field having a thickness of 34 T generated.

The magnet assemblies according to the invention each comprise an even number of partial coils (individual pancake coils), wherein each two adjacent partial coils form a double pancake coil, which can be produced by winding a slotted superconductor tape and rotating the partial coils against each other. The partial coils of a double pancake coil are in the same direction flows through the current to generate an effective magnetic field that is greater than the individual fields of the coil sections. The slotted superconductor tape from which the double pancake coil is wound represents a closed loop in which the current (once the double pancake coil is in the superconducting state) can flow lossless. An additional connection of the individual coil sections with each other is no longer necessary. This opens up the possibility of equipping MR magnet arrays with HTS band conductors and thus exploiting the advantages of HTS band conductors in magnetic resonance.

LIST OF REFERENCE NUMBERS

1

Superconductor tape

2

slot

3a, 3b

End of the superconductor band

4a, 4b

Subbands of the superconductor band

5, 5a, 5b

Double pancake coil with coils running in the same direction

5 ', 5a', 5b '

Double pancake coil with oppositely charged partial coils

6a, 6b, 6c, 6d

Part coils of double pancake coils

7a, 7b

power leads

8th

Superconducting switch

a

Axis of the partial coil

L

Longitudinal axis of the superconductor belt

MA1

Magnet arrangement with double pancake coil with radius 1

MA2, MA3

Magnet arrangement with double pancake coil with radius 2

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Laskaris, ET, Ackermann, T., Dorri, B. Gross, D., Herd, K., Minas, C., A Cryogen-Free Superconducting Magnet for Interventional MRI Applications, IEEE Transactions to Applied Superconductivity, Vol. 5, No , 2, June 1995 [0002]
• Brochure Bruker HTS YBCO Coated Conductor Data Sheet from Bruker HTS GmbH [0008]
• http://www.bruker-est.com/ybco-tapes.html [0008]
• Laskaris, ET, Ackermann, T., Dorri, B. Gross, D., Herd, K., Minas, C., A Cryogen-Free Superconducting Magnet for Interventional MRI Applications, IEEE Transactions to Applied Superconductivity, Vol. 5, No , 2, June 1995 [0010]

Claims (14)

Superconducting MR magnet assembly with a filamentless superconductor tape, characterized in that the superconductor tape ( 1 ) in the longitudinal direction (L) a slot ( 2 ) between both ends ( 3a . 3b ) of the superconductor tape ( 1 ), wherein the slot ( 2 ) is formed such that the superconductor tape ( 1 ) one the slot ( 2 ) forms an enclosed closed loop, and that the superconductor tape ( 1 ) to at least one double coil ( 5 . 5a . 5b ), the slit being the double coil ( 5 . 5a . 5b ) in two sub-coils ( 6a . 6b . 6c . 6d ), wherein at least one double coil ( 5 . 5a . 5b ) the partial coils ( 6a . 6b . 6c . 6d ) are in each case rotated relative to one another and / or displaced such that the sub-coils ( 6a . 6b . 6c . 6d ) generate a given spatial magnetic field profile in a measuring volume Magnet arrangement according to claim 1, characterized in that the double coil ( 5 . 5a . 5b ) is a double pancake coil. Magnet arrangement according to claim 1 or 2, characterized in that at least one double coil ( 5 . 5a . 5b ) the partial coils ( 6a . 6b . 6c . 6d ) are in each case rotated relative to one another and / or displaced so that both partial coils ( 6a . 6b . 6c . 6d ) each of a double coil ( 5 . 5a . 5b ) are flowed through in the same direction in current flow within the closed loop from the stream. Magnet arrangement according to one of the preceding claims, characterized in that the superconductor tape ( 1 ) to at least two double coils ( 5a . 5b ) is wound up. Magnet arrangement according to claim 4, characterized in that the double coils ( 5a . 5b ) are arranged so that the partial coils ( 6a . 6b . 6c . 6d ) of all double coils ( 5a . 5b ) are flowed through in the same direction in current flow within the closed loop from the stream. Magnet arrangement according to claim 4, characterized in that the double coils ( 5a . 5b ) are arranged so that at least one double coil is traversed in current in the closed loop in opposite directions with respect to other double coils from the stream. Magnet arrangement according to one of claims 4 to 6, characterized in that the double coils ( 5a . 5b ) have different inner radii and / or different outer radii. Magnet arrangement according to one of the preceding claims, characterized in that the partial coils ( 6a . 6b . 6c . 6d ) each of a double coil ( 5 . 5a . 5b ) are arranged coaxially with each other. Magnet arrangement according to claim 4 and 8, characterized in that the double coils ( 5a . 5b ) are arranged coaxially with each other. Magnet arrangement according to one of the preceding claims, characterized in that the superconductor tape ( 1 ) HTS material, preferably YBaCuO. Magnet arrangement according to one of the preceding claims, characterized in that the superconductor tape ( 1 ) with two power connections ( 7a . 7b ) is provided for feeding current into the loop, wherein between the power connections ( 7a . 7b ) a heatable end ( 3a ) of the superconductor tape ( 1 ) is located. Magnet arrangement according to one of the preceding claims, characterized in that the slot ( 2 ) runs in a straight line and the band in the slotted area in subbands ( 4a . 4b ) of equal width divides. MR magnet system comprising at least two magnet arrangements according to one of claims 1 to 12. MR magnet system comprising at least one magnet arrangement according to claim 1 to 12 and at least one other magnet arrangement.

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