WO2012156278A1

WO2012156278A1 - Device for producing a homogenous magnetic field

Info

Publication number: WO2012156278A1
Application number: PCT/EP2012/058660
Authority: WO
Inventors: Peter FIERLINGER; Rainer STOEPLER; Igor ALTAREV; Allard SCHNABEL
Original assignee: Technische Universität München; Bundesrepublik Deutschland
Priority date: 2011-05-19
Filing date: 2012-05-10
Publication date: 2012-11-22
Also published as: DE102011050507A1

Abstract

The invention relates to a device (1) for producing a homogenous magnetic field, comprising an inner shielding cylinder (3) supporting a conductor arrangement (7), the inner conductor track sections thereof helping to produce the homogenous magnetic field (2) inside the shielding cylinder (3). Said shielding cylinder (3) is also surrounded by additional shieldings (8 - 11). In the device, the inner shielding cylinder (3) is accessible without opening the windings (28).

Description

description

Device for generating a homogeneous magnetic field

The invention relates to a device for generating a homogeneous magnetic field with:

- A shielding device for shielding magnetic fields and

- A current acted upon conductor arrangement, with the inside of the shielding a homogeneous magnetic field can be generated.

Such a device is known from GALVAN, AD, FILIPPONE, B., CHEN, J., PLASTER, B .: Measurement of the uniformity of the SNS neutron electric dipole moment experiment, Abstract Submitted to the HAW09 Meeting of The American Physical Society, 06 July 2009 known. In the known device, a homogeneous magnetic field is generated by a cosine (Θ) coil arrangement within a series of magnetic shields

A cosine (Θ) coil arrangement is described in KHRIPLOVICH, IB and LAMOREAUX, SK: CP Violation Without Strangeness, Electric Dipole Moments of Particles, Atoms, and Molecules, Texts and Monographs in Physics, Berlin Heidelberg 1997, pp. 35-42 Individual described.

A disadvantage of the known device is that the homogeneity of the magnetic field is limited to a relatively small volume range in the interior. Thus, while it is suitable for performing experiments for determining the dipole moment of neutrons, there is also a need for corresponding devices that are dimensioned to be walkable by a human or to be used for recumbent patients. for example for medical applications. Such devices are used for biomagnetism measurements of cardiac or cerebral currents and for magnetic resonance measurements. Optically pumped alkali metal cells, SQUIDs or sensors with nuclear spin-polarized noble gases are used. The high sensitivity of these magnetic field sensors sets temporally and spatially constant as well as homogeneous

Magnetic fields ahead. For example, magnetic field sensors can be disturbed by very small vibrations in gradient fields of a few nT / m. The resulting noise can then limit the measurement accuracy and possibly even lead to incorrect measurement results. Another requirement for a corresponding apparatus is the scalability, since further applications for proportionally smaller equipment are conceivable. Examples can be found in measurement technology, in particular for gyroscopes, atomic magnetometers or measuring devices for precision standards, which must be shielded against electromagnetic and magnetic interference.

Starting from this prior art, the invention is therefore the object of an easily accessible, scalable and, if necessary, walk-in device for

Creating a homogeneous magnetic field to create.

This object is achieved by a device having the features of the independent claim. In dependent claims advantageous embodiments and developments are given.

The device has a shielding device for shielding magnetic fields, which has a hollow shielding body with a shielding jacket which revolves around a longitudinal axis. The device furthermore has a current-carrying conductor arrangement with which inside the

Shielding a homogeneous magnetic field can be generated. This conductor arrangement has at least two windings which are wound along the longitudinal axis of the shielding body around the shielding jacket of the shielding body. The wind Each has an inner conductor track section extending within the shielding body along the longitudinal axis and an outer conductor track section extending outside the shielding body along the longitudinal axis and generate a magnetic flux which is opposite to one another in the circumferential direction of the shielding body. Since the windings are wound around the shielding jacket, the shielding body is easily accessible laterally via openings which run transversely to the longitudinal axis. In particular, the interior of the shielding body can be easily entered with appropriate dimensions. Furthermore, it has been shown that the homogeneity of the magnetic field inside the shielding body is up to two orders of magnitude better than in the prior art. This is particularly due to the fact that only the current flowing through the inner trace portions contributes to the magnetic field inside the shield body, while the magnetic field generated by the current flowing back in the outer trace portions is shielded by the shield body. In one embodiment, the turns are part of at least two field coils wound around the shielding shell of the shielding body, the turns of the field coils each extending within the shielding body along the shielding body

Have longitudinal axis extending inner conductor track portion and an outside of the shield along the longitudinal axis extending outer conductor track portion and the at least two field coils generate a circumferentially opposite to each other of the shielding magnetic flux. By a larger number of conductor track sections in the interior of the shielding body, the homogeneity of the magnetic field can be further improved.

As a rule, the conductor arrangement has two field coils, which are arranged on opposite sides of the shielding jacket. The field coils are wound around the shielding jacket of the shielding body and generate a circumferential direction of the shielding body opposite each other magnetic flux. The two field coils can be wound in opposite directions, so that a single power source is sufficient for the power supply of the two field coils. In addition, it is possible to wind the two field coils in the same direction and provide separate power sources for both field coils. If each of the two field coils is connected to an associated power source, a magnetic field gradient across the

Direction of the magnetic field can be achieved in the interior of the shielding body, but the noise behavior is tended to be deteriorated by additional lhe power sources.

In a further embodiment, the shielding body has a circular cross-section and the conductor track sections extending in the interior of the shielding body have a constant spacing between one another in the direction of the magnetic field. Projected onto an axis extending in the magnetic field direction, the winding density of the conductor track sections is therefore constant. With such an arrangement, a particularly homogeneous magnetic field with a homogeneity ΔΒ / Β in the order of 10 ^{~ 5} can be generated, which is limited only by residual fields of the shielding material.

For certain applications, it can be advantageous if the magnetic field present in the interior of the shielding body has a gradient, for example for amplitude measurements in the case of vibrations or similar measurements. Such a gradient can be generated, for example, by means of additional windings which are wound around the shielding body along the longitudinal axis of the shielding body and are connected to a separate power source.

As a rule, in addition to the shielding jacket which revolves around the longitudinal axis, the shielding body also has lateral openings which cut the longitudinal axis of the shielding body and through which the interior of the shielding body is accessible. If the shielding body is arranged lying with the longitudinal axis, so that the longitudinal axis extends substantially in a horizontal direction, the interior of the shielding body is easily accessible via one of the two lateral openings of the inner shielding body.

In addition, it is possible to provide in these openings of the inner shielding conductor tracks of a compensation winding, with which caused by the finite length of the Abschirmmantels distortions of the magnetic field in

Inside the shielding can be corrected.

These compensating turns may extend along the lines of equal field strength of the magnetic field generated by the inner trace portions extending within the shield body along the longitudinal axis.

As a result, the distortions can be effectively compensated.

The conductor arrangement can each have at least two compensation coils extending along the openings at the openings of the shielding body, which are arranged one behind the other in the magnetic field direction and which generate a magnetic flux opposite to one another. The compensation windings of each compensation coil have different cross-sectional areas. The winding centers of the compensation windings are the more offset towards the outside, the smaller the cross-sectional area of the respective compensation winding. Thereby, the distortion of the generated magnetic field due to the finite extension of the shielding in the axial direction can be compensated.

In order to concentrate the compensation field on the edges of the openings, the compensation windings are kidney-shaped and arranged with their convex side outwards and with their concave side facing inwards. There are However, other arrangements and winding densities possible, which can be optimized for the appropriate application.

To suppress external magnetic fields as far as possible, the inner shielding of a multi-wall outer

Be surrounded shielding. After the demagnetization still existing residual magnetic fields of the outer shield penetrate only very limited in the interior of the inner shielding. Thus, the outer shielding device is subjected to much lower requirements and easier to manufacture.

To compensate for external magnetic fields, the outer shielding device may be arranged in an outer compensation coil arrangement.

The device can also have a plurality of longitudinally arranged in succession hollow shielding with associated

Have conductor arrangement, with each of which can generate a homogeneous magnetic field in the interior of the associated shielding. As a result, in particular elongate conductors for polarized particles can be realized.

Further advantages and features of the invention will become apparent from the following description, are explained in the embodiments of the invention with reference to the drawings in detail. Show it:

FIG. 1 shows a cross section through an apparatus for generating a homogeneous magnetic field;

Figure 2 is an exploded view of a holder for an inner shielding body of the device of Figure 1; Figure 3 is a cross-sectional view of the inner shielding body with the distribution of turns around a wall of the inner shielding body of Figure 2; Figure 4 is a perspective view of the second octant of the inner shielding body from the front;

FIG. 5 shows a plan view of a compensation coil arranged laterally on the inner shielding body, which can be mounted on both sides in the region of the openings of the shielding body;

Figure 6 is a rear perspective view of the first octant of the inner shielding body with the space points used in the following diagrams;

Fig. 7 is a diagram showing the homogeneity of the magnetic field inside the inner shielding body for various space points;

FIG. 8 is a graph showing the dependence of the magnetic field homogeneity on the length of the inner shielding body and the length of a shielding space surrounding the inner shielding body;

Figure 9 is a diagram in which the dependence of the on

Measuring points of average homogeneity of the length of the shielding space surrounding the inner shielding body is shown;

Figure 10 is a graph showing the dependence of the homogeneity on the radius of the inner cylindrical shielding body;

Figure 11 is a diagram showing the influence of openings in

Covers the inner shielding body; FIG. 12 shows a diagram in which the effect of manufacturing or assembly errors on the homogeneity of the magnetic field in the interior of the cylindrical shielding body is illustrated;

Figure 13 is a perspective view of the first octant of Figure 6 with the location of a weakened area in which the permeability of the shielding is reduced;

Figure 14 is a graph showing the effect of local weakening of the inner shielding body on homogeneity; and FIG. 15 shows an enlarged detail from the diagram

FIG. 14.

FIG. 1 shows a perspective cross-sectional view of a device 1 for generating a homogeneous magnetic field 2. The homogeneous magnetic field 2 is generated in the interior of a horizontally arranged shielding cylinder 3 by the coil 7. In FIG. 1, the cylinder axis 4 of the shielding cylinder 3 coincides with the y-axis of the Cartesian coordinate system. The magnetic field 2, which is as homogeneous as possible generated in the interior of the shielding cylinder 3, is in the direction of the z-coordinate axis in all representations. However, the spatial orientation of the entire device 1 is arbitrary.

The shielding cylinder 3 has a shielding jacket 5 which is held by support rings 6. For generating the magnetic field 2 in the interior of the shielding cylinder 3, a conductor arrangement 7 is provided, which is only indicated here, but will be described in detail below. The shielding cylinder 3 is located in a first cubic shield 8, which in turn is embedded in a second cubic shield 9. The second shield 9 is located in a third shield 10, which in turn is surrounded by a fourth shield 11. The device 1 thus comprises not only an inner shielding device formed by the shielding cylinder 3, but also an outer shielding device 12 formed by the shields 8 to 11. Such shielding devices 12 comprising a plurality of cubic shields 8 to 11 nested in one another are known to the person skilled in the art generally serve to keep external magnetic fields as far as possible from the interior of the first shield 8. With appropriate size, such nested shields are referred to as magnetic shielded cabins (MSR = magnetically shielded room). Usually, the walls of the shields 8 to 11 are made of a nickel-iron alloy based material, for example Mu metal, or an equivalent material. Furthermore, the shields 8 to 11 may also include highly conductive material such as copper or aluminum. Cubic shields, however, have intrinsic residual magnetic fields of several nTs at a typical distance of 10 cm from that due to the angular geometry

Surface of the highly permeable material. These residual magnetic fields can not be completely removed even by demagnetization. In order additionally to be able to compensate for external magnetic fields, such as the earth's magnetic field, both statically and dynamically (ie actively), the outer shield 11 is surrounded by an external compensation coil arrangement 13, which is only schematically illustrated in FIG. 1 and which, for example, consists of the three outer compensation coils 14 is formed, which are each executed in the manner of Helmholtz coils. The compensation coils 14 each compensate for the magnetic field in a spatial axis. Thus, the ambient magnetic field in the interior of the compensation coil arrangement 13 can be compensated with the compensation coils 14 in a known manner as a function of the number of the compensation coils 14 up to a certain order. As will be explained in more detail below, the device 1 can be scaled arbitrarily, wherein the screen factor of the outer shield 8 to 11 with smaller dimensions increases sharply. Therefore, scaling to smaller dimensions may eliminate the shields 9 to 11 and retain only the innermost shield 8. The device 1 can thereby be made much easier. In the outer dimension of the outer shield 11 of approximately four meters, as shown in FIG. 1, a space approximately 2.5 m in length and 2.5 m in diameter is available inside the shielding cylinder 3 for experiments and examinations which are weak but for this require extremely homogeneous magnetic field 2. Such an examination device 15 is indicated in FIG. 1 in the interior of the shielding cylinder 3. The lines 16 required for the examination device 15 and the supply of the conductor arrangement 7 with current are guided through openings 17 to the outside.

In order to make the interior of the shielding cylinder 3 accessible, side walls 18 of the shielding rooms 8 to 11 may be removable, hinged or provided with doors. FIG. 2 shows an exploded view of the internal structure of the device 1. The shielding cylinder 3 is provided at both ends with flanges 19 which hold the inner conductor track sections 20 extending inside the shielding cylinder 3 and outer conductor track sections 21 extending outside the shielding cylinder 3. For this purpose, the flanges 19 are provided with bushings 22, through which the inner conductor track sections 20 and the outer conductor track sections 21 can be guided. For the sake of clarity, only one outer conductor track section 21 and two of the inner conductor track sections 20 running essentially parallel to the cylinder axis 4 are shown. On the flanges 19 can also be a rear cover 23 and a front Cover 24 are attached. The rear cover 23 and the front cover 24 are integrated into the walls 25 of the first shield 8. In the rear cover 23 and the front cover 24, passages 26 of different diameters may be formed. The shielding cylinder 3 is finally held by a support structure 27, to which also the longitudinally extending walls 25 of the first shield 8 can be attached. The shielding cylinder 3 is made of a highly permeable material. As the material for the shielding cylinder 3 in particular materials based on a nickel-iron alloy in question, for example Mu metal, based on metallic glasses produced materials, such as Metglas, or materials based on cobalt alloys, for example Vitrovac , As a rule, however, Mu metal is currently used.

FIG. 3 shows a cross-sectional view through the screening cylinder 3 and the conductor arrangement 7, wherein the current direction in the inner conductor track sections 20 and the outer conductor sections 20 is shown in FIG

Track sections 21 are marked by dots and crosses. A dot denotes a stream coming out of the

Paper level leads out and a cross denotes a stream, which leads into the plane of the paper.

If on the circumference of an infinitely long cylinder assuming a uniformly infinitely densely packed conductor arrangement whose conductors are aligned at right angles to the circular cross-section of the cylinder, so everywhere in the interior of the Abschirmzylinders 3 a homogeneous magnetic field 2 is generated when the current I at each location x an inner conductor section 21 on the circle the relationship

Fulfills. All geometric and physical constants are summarized in the pre-factor c. In the arrangement shown in Figure 3, the approximate solution for the

Coil arrangement, which results under the condition of an equal current in all conductors, shown. The inner conductor track sections 20 located in the interior of the shielding cylinder 3 in the direction of the magnetic field 2 have a constant height spacing h from each other. The winding density projected on the z-axis is therefore constant. For h _^ O, the approximate solution transforms into the exact solution. Inhomogeneities due to the approximation increase with the distance from the circle center to the cylinder jacket and to the top surfaces of the only finely long cylinder. However, as shown below, these inhomogeneities can be corrected according to the requirements.

If the shielding cylinder 3 has a cross section deviating from the circular area, the arrangement of the inner conductor track sections 20 is to be modified so that the above-mentioned condition for the equivalent current remains satisfied on a virtual circle. The magnetic field within the virtual circle is then still homogeneous.

In the exemplary embodiment illustrated in FIG. 3, the inner conductor track sections 20 and the outer conductor track sections 21 each form windings 28 that run along the

Longitudinal axis of the shielding body are wound around the shielding jacket 5 and form two field coils 29 and 30, which in a circumferential direction 31 each generate mutually opposite magnetic fluxes. This can be accomplished by winding the two field coils 29 and 30 in opposite directions and connecting them to a common power source, or by oppositely polarizing both field coils 29 and 30 outside the device 1 to a common one

Power source are connected. In addition, it is also conceivable to connect both field coils 29 and 30 to separate power sources. However, this would be fluctuations of the Current sources lead to inhomogeneities of the magnetic field 2. On the other hand, a magnetic field gradient in the cross-sectional area transverse to the magnetic field direction can thereby be generated.

CIOFI et al., IEEE Transactions on Instrumentation and Measurement Volume 47, 1 (1998) page 78 are typically used as current sources, which show optimized noise behavior for currents of 1-100 mA up to the DC range.

The prerequisite for a stable homogeneous magnetic field 2 in the interior of the shielding cylinder 3 is an idealization of the shielding cylinder 3. An idealization is a demagnetization in an existing magnetic field. In the present case, the material of the shielding cylinder 3 is idealized to the magnetic field 2 generated by the field coils 29 and 30. In the process, the shielding cylinder 3 is demagnetized when the magnetic field 2 is switched on. For demagnetization another, not shown Entmagnetisierungsspule is used, which is wound around the shielding of the Abschirmzylinders 3. It circumscribes the shielding material of the shielding cylinder 3 in the same way as the field coil 29 or 30. However, no special requirements are placed on the geometric orientation of the demagnetization coil. However, the current carrying capacity of the degaussing coil must be sufficient in order to be able to drive the shielding cylinder 3 into magnetic saturation. As a rule, a degaussing coil with few turns and a large conductor cross-section is used. To control the saturation, an induction coil with a small cross-section can be installed. Due to the cylindrical geometry of the shielding cylinder 3, the field generated by the degaussing coil is driven by a magnetic path having a constant length regardless of the position along the cylinder axis 4. The shielding cylinder 3 can be easily demagnetized or idealized. The stray field influences can be controlled by a reduce the integer number of turns of the demagnetization coil with opposite turns. In this case, the degaussing coil does not generate a magnetic field on the cylinder axis 4.

An idealization is also necessary for the cubic shields 8 to 11 in FIG. For this purpose, degaussing coils, not shown, are wound around the individual edges of the cubic shields 8 to 11. It is essential that the demagnetization coils wrap around a side wall of the cubic shields 8 to 11, which does not necessarily have to take place at the edge, and that at least one demagnetization coil is present per spatial axis. In order to reduce the electrical power necessary for idealization, each of the cubic shields 8 to 11 may be separately idealized. The interior of the inner cubic shield 8 on the magnetic field 2 can be idealized by sequentially perfecting the series-connected demagnetization coils of one of the cubic shields 8 to 11 in one spatial direction.

Although each of the cubic shield 8 to 11 is not idealized as a whole from the saturation out, but for each demagnetization is performed again with a quasi-constant magnetic path.

FIG. 4 shows a perspective view of an octant 32 of a model of the shielding cylinder 3 reduced by a factor of two. This is the second octant, if it is assumed that the coordinate system is located in the center of the screening cylinder 3 and has the orientation shown in the figures. As will be explained in detail below, such a model of the shielding cylinder 3 was used for simulation calculations to determine the magnetic field homogeneity in the interior of the shielding cylinder 3. In Figure 4, the shield 5 of the shielding cylinder 3 can be seen. Along the longitudinal axis of the shielding body, the windings 28 of the conductor arrangement 7 are wound around the shielding jacket 5 of the shielding cylinder 3. Between the windings 28 of the field coils 29 and 30 are also trim turns 33, which are part of a trimming coil 34 with which a magnetic field gradient can be achieved inside the shielding cylinder 3 and which can also be used to correct mechanical deformations.

In Figure 4, a portion of the front cover 24 is further shown, which is provided on its facing the center of the Abschirmzylinders 3 inside with compensation windings 35 forming part of an inner compensation coil 36, which caused by the finiteness of the axial extent of the Abschirmzylinders 3 Inhomogeneity of the magnetic field 2 can be compensated. Furthermore, openings 37a, 37b, 37c, 37d introduced into the front cover 24 are shown in FIG. 4, which may be mechanical or magnetic openings. Mechanical openings are, for example, feedthroughs for lines and media. For example, a magnetic opening is created by the high permeability material forming the front cover 24 losing its high permeability due to localized mechanical stress such as impact on the front cover 24.

In Figure 5, the arrangement of the compensation coils 36 is shown in plan view. The two compensation coils 36 arranged one behind the other in the z-direction generate opposite magnetic fluxes to each other. For this purpose, the compensation coils 36 are either wound in the opposite direction or wound in the same direction and oppositely poled to a common or connected to an associated power source. The compensation coils 36 further comprise compensation windings 35 with different cross-sectional areas arranged in a surface, the winding centers 38 of which are offset further outward along the magnetic field 2, the smaller the cross-sectional area of the respective compensation winding 35. The inner compensation windings 35 with a smaller cross-sectional area compared to the outer compensation windings 35 are therefore offset further outwards. The compensation windings 35 should follow the lines of equal field strength of the magnetic field 2 generated by the field coils 29 and 30. Therefore, the compensation windings 35 have a kidney-shaped cross-sectional profile, wherein the compensation windings 35 are arranged with their convex side facing outwards and with their concave side facing inwards. Thus, the compensation magnetic field is concentrated on the outer edges of the compensation coils 36.

In order to prove the homogeneity of the magnetic field 2 inside the device 1, simulation calculations were carried out and the distribution of the magnetic field in the interior of the shielding cylinder 3 was calculated.

FIG. 6 shows a rear view of a first octant 39 of the model of the shielding cylinder 3. In addition to the shielding jacket 5, the front cover 24 is also shown, into which a further opening 37e is inserted in addition to the openings 37a-c. Furthermore, the position of subsequently used spatial points PI to P8 is shown in FIG. It should be noted that the simulation calculations have been carried out for a prototype which has approximately half the dimensions of the device shown in FIG. The coordinates of the spatial points PI to P8 are listed in Table I listed in the Annex. It can be seen from Table I that the space points span a cylindrical volume with a height of 30 cm and a diameter of 30 cm. Since the calculations are based on the linear Maxwell equations, the simulations also apply to a scaled device that is larger or smaller than the device 1.

FIG. 7 shows a diagram in which the results of the simulation calculation for the spatial points PI to P8 are shown. It can be seen from FIG. 7 that the relative deviation of the components B _x , B _y and B _{z of} the magnetic field 2 from a magnetic field Bo in the z-direction moves in the range 10 ^~5 . Thus, the homogeneity of the magnetic field 2 in the region of the spatial points PI to P8 is better by about two orders of magnitude than in known devices.

The fact that the returning currents are led back outside the screening cylinder 3 contributes to the great homogeneity of the magnetic field 2. In addition, also carry the

Compensation coils 36 for the homogeneity of the magnetic field 2 at the spatial points PI to P8 at.

FIG. 8 shows the relative deviation of the z-component of the magnetic field 2 at the spatial points PI to P8 for five different lengths L _{s of} the shielding cylinder 3 and inner dimensions L _{r of} the inner shielding chamber 8. The respective model configurations are listed in Table II. Since only the relative behavior was investigated, it was possible to dispense with the compensation coils 36. It can be seen from FIG. 8 that the relative deviation of the z component of the magnetic field ² lies in the range 10 ^-2 .

FIG. 9 shows the relative deviation of the z-component over the inner dimension L _{r of} the inner shielding space 8 of the various models, averaged over the spatial points P 1 to P 8. As the length of the shielding cylinder 3 has been chosen to be progressively greater as the length L _{r of} the shielding space 8 increases, it can be seen that the longer the shielding cylinder 3 is, the greater the homogeneity and the greater the distance between the shielding cylinder 3 and the wall of the innermost one Shielding space 8 is. At the same time With reference to FIGS. 8 and 9, it is clear that a suitable compensation coil 36 at the ends of the shielding cylinder 3 contributes substantially to the homogeneity of the magnetic field 2, since the homogeneity without the compensation coils is in the range of 10 ^-2 .

The dependence of the homogeneity of the magnetic field 2 on the radius of the shielding cylinder 3 was also investigated. FIG. 10 shows the relative deviation of the z-component of the magnetic field 2 for the spatial points PI to P8 at a constant length of the shielding cylinder 3 along the y-axis and different cross-sectional dimensions along the x-axis and the z-axis. The dimensions of the models F to H used are listed in Table III in the appendix, with the lengths in the x, y and z directions referring to the Cartesian coordinate system shown in FIG. It can be seen from FIG. 10 that the radius has no significant influence on the homogeneity of the magnetic field 2 when the length of the shielding cylinder 3 is kept constant. The meaning of the front and rear ends of the shielding cylinder 3 will be also apparent from FIG. 11, in which a diagram illustrates the relative deviation of the z-component for the space points PI to P8 in the case where the front cover 24 or the rear cover 23 the openings 37a-d corresponding openings are formed. The relative deviations are respectively related to the case that no recesses corresponding to the openings 37a-d are included in the rear cover 23 and the front cover 24. A model hl refers to the case that the openings 37a and 37b at the front

Cover 24 are formed. Another model h3 simulates the case that the opening 37c at the top of the front Cover 24 is present and a model h4 refers to the case that the opening 37d is formed at the bottom of the front cover 24. Each of these openings causes the homogeneity of the magnetic field 2 to deteriorate.

The latter is also the case if 3 inaccuracies occur during assembly or in the production of the shielding cylinder. The diagram shown in FIG. 12 shows the dependence of the relative accuracy of the z component of the magnetic field 2 for the different measuring points PI to P8 for different manufacturing errors. These manufacturing defects correspond approximately to the expected mechanical tolerances. However, the errors in the magnetic field 2 resulting from such mechanical deformations can be almost completely compensated by adjusting the currents in the trim turns 33 and in the compensation coils 36.

Finally, the influence of an opening 40 shown in FIG. 13 in the shielding jacket 5 can be illustrated with reference to FIGS. 13 to 15. This opening 40 is located substantially above the measuring volume spanned by the spatial points PI to P8. If the permeability in the region of the opening 40 decreases, the homogeneity of the magnetic field 2 in the interior of the shielding cylinder 3 deteriorates, as shown in FIG. FIG. 14 shows a diagram in which the dependence of the relative deviation of the z component of the magnetic field 2 on the permeability in the region of the opening 40 is shown. FIG. 15 shows an enlarged detail of the diagram shown in FIG. It can be seen from FIG. 15 that the permeability may vary only by about ± 20% by the permeability in the shielding jacket 5 of _μΓ = 25,000 in order to keep the homogeneity of the magnetic field 2 in the interior of the shielding cylinder 3 in the range of 10 ^~5 , In the apparatus described here, the interior of the shielding cylinder 3 is freely accessible without the windings 28 having to be separated. It should also be emphasized once again that the device described here is arbitrarily scalable. In this respect, even in larger volumes than the measuring volume spanned by the spatial points PI to P8, a homogeneous magnetic field with a relative deviation of 10 ^-5 can be generated. Likewise, homogeneous magnetic fields can be produced for very small measurement setups, which can be integrated, for example, in measuring instruments.

The shielding against external fields is accomplished by the nested shields 8 to 11. Shade factors of 100,000 at 0.01 Hz with 4 m outer edge length can be achieved. The shielding factor of such shielding results from the ratio of an external sinusoidal excitation of about 2 μΤ peak to peak and a frequency of 0.01 Hz compared to the maximum occurring magnetic field fluctuation of 0.01 Hz in the interior. By actively compensating external noise fields using the outer Helmholtz coil assembly 13 and a fluxgate magnetometer, the internal fluctuations can be reduced to 100 f T at 0.01 Hz.

Another advantage of the device 1 is that the shielding is dependent on the generation of the magnetic field 2 inside the

Shielding cylinder 3 is largely decoupled. As a result, magnetic residual fields, which arise due to faults in the shielding device 12 and during demagnetization or idealization of the shielding device 12, can be kept away from the interior of the shielding cylinder 3. The shielding cylinder 3 can be almost completely idealized due to missing corners, so that no additional static magnetic interference fields due to incomplete idealization are present in the interior of the shielding cylinder 3. The device 1 described here can therefore be constructed modularly from independent functional components.

As such, a commercial shielding device may be used for the outer shielding device 12. In comparison to a commercially available shielding, however, a better homogeneity of the magnetic field 2 by at least a factor of 10 than in the prior art can be achieved.

Finally, the device 1 described here can also be used to create a polarized particle conductor inside which a homogeneous magnetic field is formed. For this purpose, the shielding cylinder 3 may have a length corresponding to the required length of the conductor. In addition, it is possible to arrange a plurality of shielding cylinders 3 behind one another within the shields 8 to 11 and to provide each of the shielding cylinders 3 with an associated conductor arrangement 7. The Kompensati- onsspulen 36 need then be arranged only at the two ends of the tube, which is formed by the successively arranged Abschirmzylindern 3.

Finally, it should be noted that features and properties associated with a particular

Embodiment described can also be combined with another embodiment, except if this is excluded for compatibility reasons. Finally, it should be noted that in the claims and in the description, the singular includes the plural unless the context indicates otherwise. In particular, when the indefinite article is used, it means both the singular and the plural. Table I:

Table II:

Table III:

Configuration Y X z

F 2.3 1.6 1.6

G 2.3 1.8 1.8

H 2.3 2.0 2.0

Claims

claims

1. Device for generating a homogeneous magnetic field with:

- A shielding device for shielding magnetic fields and

a conductor arrangement (7), which can be acted upon by current, with which a homogeneous magnetic field (2) can be generated inside the shielding device,

characterized in that the shielding device comprises a hollow shielding body (3) with a shielding jacket (5) encircling a longitudinal axis (4) of the shielding body (3), and in that the conductor arrangement (7) has at least two windings (28) running along the Longitudinal axis (4) are wound around the shielding shell (5) of the shielding body (3) and each one within the shielding (3) along the longitudinal axis (4) extending inner conductor track portion (20) and one outside of the shielding body (3) along the longitudinal axis (4) extending outer conductor track portion (21) and which generate in the circumferential direction (31) of the shielding (3) opposite each other magnetic flux.

2. Apparatus according to claim 1,

characterized in that the turns (28) are part of at least two field coils (29, 30) which are wound around the shielding jacket (5) of the shielding body (3), the turns (28) of the field coils (29, 30) each having a in the shielding body (3) along the longitudinal axis (4) extending, inner conductor track portion (20) and an outside of the shielding body (3) along the longitudinal axis (4) extending outer conductor track portion (21), and in that the at least two field coils (29 , 30) generate a magnetic flux opposite to each other in the circumferential direction (31) of the shielding body (3).

3. Apparatus according to claim 1,

The conductor arrangement (7) has two field coils (29, 30) which are arranged on opposite sides of the shielding jacket (5) and which surround the shielding jacket (5) of the shielding jacket (5)

Shielding body (3) are wound and the one in the circumferential direction (31) of the shielding (3) generate mutually opposite magnetic flux.

4. Apparatus according to claim 3,

d a d u r c h e g e n e c e s, the shielding body (3) has a circular cross-section and that the conductor track sections (20) running inside the shielding body (3) have a constant spacing when projected onto a spatial axis extending in the direction of the magnetic field (2).

5. Device according to one of claims 1 to 4,

d a d u r c h e k e n e, the conductor arrangement (7) along the longitudinal axis (4) around the

Shielding jacket (5) of the shielding (3) wound coils (33), with which a magnetic field gradient can be generated in the interior of the shielding (3).

6. Device according to one of claims 1 to 5,

d a d u r c h e k e n e z e i n h e, e s s of the shielding (3) has the longitudinal axis (4) intersecting openings.

7. Device according to one of claims 1 to 6,

d a d u r c h e k e n e z e i n h e, t a s s of the shielding (3) with the longitudinal axis (4) is arranged lying.

8. Apparatus according to claim 6 or 7,

characterized in that the shielding body (3) has at least one opening through which the interior of the shielding body (3) is accessible without a separation of one of the turns (28).

9. Device according to one of claims 1 to 8,

That is, the shielding body (3) has a front opening and a rear opening, and the conductor arrangement (7) has at least one compensating turn (35) extending along the openings of the shielding body (3) at the front opening and at the rear opening.

10. Apparatus according to claim 9,

and the compensating turns (35) extend along the lines of equal field strength of the magnetic field generated by the inner trace portions (20) extending along the longitudinal axis (4) within the shield body (3).

11. The device according to claim 10,

characterized in that the conductor arrangement (7) at the front-side opening and at the rear-side opening in each case at least two compensation coils (36) extending along the front-side opening and the rear opening, which are arranged one behind the other in the magnetic field direction and which have a mutually opposite magnetic Create river.

12. Device according to claim 11,

characterized in that the compensation coils (36) comprise compensating windings (35) with different cross-sectional areas arranged in a surface, whose winding centers (38) are displaced further outwards the smaller the cross-sectional area of the respective compensation winding (35).

13. Device according to claim 12,

The compensating windings (35) have a kidney-shaped cross-sectional profile and are arranged with their convex side facing outward and with their concave side facing inwards.

14. Device according to one of claims 1 to 13,

characterized in that the shielding body (3) by an at least single-walled outer shielding device (8-11, 12) is surrounded, said walls (18) of the shielding device (8-11, 12) for the demagnetization of the shielding device (8-11 , 12) are each wrapped with at least one Entmagnetisierungswindung.

15. Device according to one of claims 1 to 14,

The device comprises an external compensation coil arrangement (13) arranged outside the shielding device.

16. Device according to one of claims 1 to 15

The device has a plurality of hollow shielding bodies (3) with associated conductor arrangement (7) arranged one behind the other in the longitudinal direction, with which a homogenous magnetic field can be generated in each case in the interior of the associated shielding body (3).