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Title:
MAGNET GRID
Document Type and Number:
WIPO Patent Application WO/2014/191890
Kind Code:
A1
Abstract:
The invention is a new arrangement of magnets in the pattern of a geometrically symmetrical grid, lying on a plane or non-plane surface. Said arrangement produces a configuration of magnetic field that is asymmetrical with respect to the surface on which the grid lies. The magnet grid can be provided with openings for the passage of particles, gases or other fluids. The configuration does not require ferromagnetic materials but only permanent magnets or electromagnets. The asymmetry can be modified by varying the geometry of the magnets or their residual induction.

Inventors:
CHITARIN GIUSEPPE (IT)
Application Number:
PCT/IB2014/061710
Publication Date:
December 04, 2014
Filing Date:
May 26, 2014
Export Citation:
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Assignee:
CONSORZIO RFX (IT)
International Classes:
H01F7/02; B03C1/033; H01J27/14
Foreign References:
US6285097B12001-09-04
Other References:
KURODA T: "Development of high current negative ion source", FUSION ENGINEERING AND DESIGN, ELSEVIER SCIENCE PUBLISHERS, AMSTERDAM, NL, vol. 36, no. 1, 1 April 1997 (1997-04-01), pages 143 - 156, XP004126121, ISSN: 0920-3796, DOI: 10.1016/S0920-3796(97)00019-7
CREMER T ET AL: "Planar permanent magnet multipoles: measurements and configurations", PARTICLE ACCELERATOR CONFERENCE, 1995., PROCEEDINGS OF THE 1995 DALLAS, TX, USA 1-5 MAY 1995, NEW YORK, NY, USA,IEEE, US, vol. 2, 1 May 1995 (1995-05-01), pages 1378 - 1380, XP010165965, ISBN: 978-0-7803-2934-8, DOI: 10.1109/PAC.1995.505228
TANAKA M ET AL: "Investigation of beam deflection reduction and multi-beamlet focus at a large-area negative ion source for a neutral beam injector with 3-D beam trajectory simulation", NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH. SECTION A: ACCELERATORS, SPECTROMETERS, DETECTORS, AND ASSOCIATED EQUIPMENT, ELSEVIER BV * NORTH-HOLLAND, NETHERLANDS, vol. 449, no. 1-2, 1 July 2000 (2000-07-01), pages 22 - 35, XP004208059, ISSN: 0168-9002, DOI: 10.1016/S0168-9002(99)01468-0
K. HALBACH: "Fields and first order perturbation effects in two-dimensional conductor dominated magnets", NUCL. INSTRUMENTS AND METHODS, vol. 78, 1970, pages 185 - 198
J. C. MALLISON: "One-sided fluxes - A magnetic curiosity?", IEEE TRANSACTIONS ON MAGNETICS, vol. 9, no. 4, December 1973 (1973-12-01), pages 678 - 682
K. HALBACH: "Design of permanent multipole magnets with oriented rare earth cobalt material", NUCL. INTRUMENTS AND METHODS, vol. 169, 1980, pages 1 - 10
S. M. LUND; K. HALBACH: "Iron-free permanent magnet systems for charged particle beam optics", FUSION ENGINEERING AND DESIGN, vol. 32-33, 1996, pages 401 - 415
F. BLOCH; O. CUGAT; G. MEUNIER; J. C. TOUSSAINT: "Innovating approaches to the generation of intense magnetic fields: Design and optimization of a 4 Tesla permanent magnets flux source", IEEE TRANSACTIONS ON MAGNETICS, vol. 34, no. 5, September 1998 (1998-09-01), pages 2465 - 2468
P. SUOMINEN; O. TARVAINEN; H. KOIVISTO: "3D-simulation studies of the modified magnetic multipole structure for an electron cyclotron resonance ion source", NUCL. INSTRUMENTS AND METHOD SUB PHYSICS RESEARCH B, vol. 225, 2004, pages 572 - 578
J. E. HILTON; S. M. MCMURRY: "An adjustable linear Halbach array", JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, vol. 324, 2012, pages 2051 - 2056
P. JIN; S. FANG; H. LIN; X. WANG; S. ZHOU: "A novel linear and rotary Halbach permanent magnet actuator with two degrees of freedom", JOURNAL OF APPLIED PHYSICS, vol. 111, 2012, pages 07E725 - 07E725,3
K. MENZEL; C. W. WINDT; J. A. LINDNER; A. MICHEL; H. NIRSCHL: "Dipolar openable Halbach magnet design for high-gradient magnetic filtration", SEPARATION AND PURIFICATION TECHNOLOGY, vol. 105, 2013, pages 114 - 120
Attorney, Agent or Firm:
BENETTIN, Maurizio (via Sorio 116, Padova, IT)
Download PDF:
Claims:
CLAIMS

1. Grid (G) of permanent magnets (Ml, M2) or electromagnets, arranged symmetrically with respect to a surface (S) and aligned in one or more arrays according to at least two genetically incident directions (Dl) and (D2) so as to form said grid (G) lying on said surface (S), characterized in that:

• the magnets (Ml) belonging to said one or more arrays geometrically aligned according to the first direction (Dl) are magnetized in the direction orthogonal to said surface S;

· the magnets (M2) belonging to said one or more arrays geometrically aligned according to the second direction (D2) are magnetized in the direction parallel to the surface S;

• said grid (G) defines openings (A) that allow the passage of particles, gases or other fluids through said surface (S),

and wherein the magnetic field produced by said grid (G) of magnets (Ml,

M2) has an asymmetrical configuration with respect to said surface (S), so that the magnetic field on one side of said surface (S) is more intense than the magnetic field on the other side of the same surface (S).

2. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to claim 1, characterized in that said magnets (Ml) belonging to said arrays geometrically aligned according to said first direction (Dl) are magnetized in an alternate manner on successive arrays.

3. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to claims 1 or 2, characterized in that said magnets (M2) belonging to said arrays geometrically aligned according to said second direction (D2) are magnetized in an alternate manner on successive arrays.

4. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, characterized in that it can be extended in said two directions (Dl) and (D2) of said surface (S) by varying the number of said arrays of magnets (Ml, M2).

5. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, characterized in that said asymmetry of the electromagnetic field produced by said grid (G) can be controlled by varying the size or the residual magnetic induction of all or part of said used magnets (Ml, M2).

6. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, characterized in that said surface (S) is plane.

7. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, characterized in that said surface (S) is curved.

8. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, characterized in that said surface (S) is cylindrical.

9. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, characterized in that said openings (A) are arranged regularly.

10. Grid (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, characterized in that said magnets (Ml, M2) have the shape of right or oblique hexahedrons.

11. Ion extraction and/or acceleration grid, characterized in that it comprises at least one of said grids (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, for a negative ion accelerator with effective filtering of the electrons and minimum deflection of the ion beam.

12. Magnetic filter suited to separate and hold back magnetic particles dispersed in a fluid, characterized in that it comprises at least one of said grids (G) of permanent magnets (Ml, M2) or electromagnets according to the preceding claims, wherein said fluid flows through said openings of said grid (G) so that the magnetic particles present in the fluid itself are effectively held back.

Description:
MAGNET GRID

DESCRIPTION

The present patent relates to grids of magnets, and in particular it concerns a new grid of magnets, specially arranged to produce a magnetic field configuration which is asymmetrical with respect to the surface on which the grid lies.

The present patent relates in particular to a new arrangement of magnets, permanent magnets or electromagnets, in the shape of a grid lying on a planar or non-planar surface, said grid being geometrically symmetrical with respect to said surface. This arrangement produces a magnetic field configuration which is asymmetrical with respect to the surface on which the grid lies. The grid of magnets may be provided with openings for the passage of particles, gases or other fluids. The configuration requires no ferromagnetic materials, only permanent magnets or electromagnets.

The arrangement of the magnets and the magnetic configuration were developed by Consorzio RFX in the context of research on high temperature magnetically confined plasmas.

The configuration is particularly efficient at filtering and retaining microscopic, nanometric or even elementary particles which pass through the grid and which by their nature can be deflected by the magnetic field.

The system uses a metal grid in which magnets, preferably permanent magnets, are inserted, according to the new arrangement that produces a magnetic field configuration that is asymmetrical with respect to the surface on which the grid lies. A more intense transverse magnetic field generated on the upstream side of the grid deflects the particles, preventing them from passing through the grid. This transverse magnetic field slightly deflects even negative ions, the trajectory of which can however be straightened by the weaker transverse magnetic field generated on the downstream side of the grid. By appropriately controlling the asymmetry of the magnetic configuration between the upstream and downstream sides of the grid, it is possible to minimize the total deflection of the ions that are extracted and accelerated, for the optimal focusing of the beam of negative ions.

State of the art

Arrangements of magnets according to a geometrically symmetrical plane grid which generate a magnetic field configuration that is symmetrical with respect to the plane of the grid itself are already known.

Arrangements of magnets according to a geometrically asymmetrical plane grid which generate a magnetic field configuration that is asymmetrical with respect to the plane of the grid are also known.

Furthermore, arrangements of magnets on a plane grid, combined with ferromagnetic material arranged in a geometrically asymmetrical pattern, which produce a magnetic field configuration that is asymmetrical with respect to the plane of the grid are also known.

In addition, arrays of magnets arranged on a surface (flat or cylindrical Halbach array) that is geometrically symmetrical and without openings are also known, which generate a magnetic configuration that is asymmetrical with respect to the symmetry surface.

Advantages

The main advantages of the new grid of specially arranged magnets and of the corresponding magnetic configuration are the following:

The magnets are arranged in a grid with openings at regular intervals, the openings of the grid can be used for the passage of particles, gases or other fluids.

The magnets are symmetrical and arranged in a geometrically symmetrical manner with respect to a surface, which simplifies the construction of the magnets and their insertion into a suitable support structure.

The magnetic field on one side of the grid is more intense compared to the magnetic field on the other side. The reduction of the magnetic field obtained on one side of the grid corresponds to an increase of the magnetic field on the other side. The asymmetry can be controlled by varying the size or the residual magnetic induction of the magnets used, until nearly cancelling the field in the vicinity of one of the two sides of the grid.

Therefore the arrangement allows the magnetic field to be effectively concentrated on one side of the grid, obtaining an intense field similar to the one that would be obtained using also ferromagnetic material in addition to the magnets.

Other plane configurations generate an asymmetrical magnetic field and are geometrically symmetrical, but require the arrangement of the magnets so as to form a continuous surface, devoid of openings as in the so- called "Halbach array".

Other plane configurations generate an asymmetrical magnetic field and allow the presence of openings at regular intervals, but require magnets which are geometrically asymmetrical with respect to the plane or arranged in a geometrically asymmetrical configuration with respect to the plane, or even require the introduction of ferromagnetic material arranged asymmetrically with respect to the plane of the grid.

Possible applications

Various different applications are possible, for example:

Extraction or acceleration grid for a negative ion accelerator featuring effective filtering of electrons and minimum deflection of the ion beam. In this type of accelerator, a plasma made up of positive and negative ions and electrons is generated in a special chamber. One wall of the chamber, called plasma grid, is provided with openings at regular intervals. Using this grid, negatively charged particles, both negative ions and electrons, can be extracted from the plasma, which, using an appropriate electric field, are accelerated towards another grid, called extraction grid, and then towards further subsequent grids, called acceleration grids, in order to generate a high-energy and well-focused beam of negative ions.

The new magnetic configuration described herein can be advantageously used in the extraction grid or in one of the acceleration grids of a negative ion accelerator. In fact, the transverse magnetic field upstream of the grid of magnets allows the electrons to be considerably deflected, preventing them from passing through the openings of the grid itself. On the contrary, the ions, being deflected to a lesser extent by the magnetic field, can pass through the openings and are then deflected in the opposite direction by the magnetic field downstream of the grid. By appropriately adjusting the ratio between the transverse magnetic field upstream and downstream of the grid, the new configuration allows the final deflection of the ions to be minimized, thereby obtaining a well-focused beam.

Magnetic filter to separate and retain magnetic particles dispersed in a fluid flowing through the grid. The grid can be arranged on a plane surface or on a cylindrical surface and, thanks to the openings and to the "concentration" effect of the magnetic field on one side of the grid with respect to the other side, it is able to effectively retain the magnetic particles present in the fluid. Contrary to other types of magnetic filters, the presence of the openings in the magnetic configuration allows the fluid to pass through, instead of skimming, the surface on which the magnets are arranged and thus ensures a more effective filtering of any magnetic particles.

Description

The new arrangement of magnets and the corresponding magnetic configuration have the following characteristics.

The arrangement of magnets is formed by two or more arrays of magnets, permanent or non-permanent, preferably having the shape of a right or oblique hexahedron, arranged aligned along at least two genetically incident directions, for example orthogonal or non-orthogonal to each other, so as to form a grid lying on a plane surface or a curved surface. The grid can be formed by one or more types of said magnets, different for their geometrical dimensions and/or different for the magnetic characteristics of the materials.

Said grid of magnets defines openings in the shape of a right-angled or skew quadrilateral.

Said openings may allow the passage of particles, gases or other fluids through said grid.

Said magnets are arranged in a geometrically symmetrical manner with respect to the surface on which said grid lies.

Said arrangement can be replicated at will along said two directions of said surface.

In the case of a grid arranged on a plane surface, even though the magnets are arranged in a geometrically symmetrical manner with respect to the plane, the configuration of the magnetic field they produce is asymmetrical with respect to the same plane.

In the case of a grid arranged on a plane surface, the magnetic field on one side of the plane is more intense than the magnetic field on the other side. The asymmetry can be controlled by varying the size or the residual magnetic induction of the magnets used or their residual magnetic induction. The characteristics of the present invention will be better clarified by the following description with reference to the drawings that are attached hereto by way of non-limiting example.

Particular reference is made, by way of non-limiting example, to the accompanying drawings (Figures 1, 2, 3, 4, 5, 6, 7) referring to a grid (G) lying on a plane surface (5).

Figure 1 schematically shows an example of the new arrangement of magnets (Ml, M2) on a grid (G) lying on a plane surface (S). The magnets are arranged in a geometrically symmetrical manner with respect to the surface (S). The orientation of the magnets (Ml, M2) is indicated in the figure by the arrows. Said grid (G) of magnets (Ml, M2) is symmetrically arranged with respect to said surface (S), comprising a part (Ga) of the magnets (Ml, M2) on one side of the surface (S) and a second part (Gb) of the magnets (Ml, M2) on the other side of the surface (S). The second part (Gb) of the magnets (Ml, M2), located behind said plane surface (S), is indicated with a dashed line.

Figure 2 schematically shows a cross section of the grid (G) of magnets (Ml, M2) on the surface (S). The orientation of the magnets (M) is indicated by arrows, the "X" indicates the incoming field in the surface (S) or the "O" indicates the outgoing field from the surface. The grey areas are occupied by the magnets (Ml, M2) while the white square areas are the openings (A) between the magnets (Ml, M2).

Figures 3a and 3b indicate respectively two sections of the grid (G) of magnets (Ml, M2) according to the section lines A-A and B-B drawn in Figure 2. Figure 4 shows an example of the arrangement of the magnets (Ml, M2) used for the calculation, where the grid (G) of magnets (Ml, M2) lies on the vertical plane xy. The magnets (Ml) of the one or more arrays aligned in a first direction (Dl), for example horizontal, have for example a 5.6 x 4.6 mm 2 cross section and have a residual induction B = 1.1 T in the direction z perpendicular to the plane. The magnets (M2) of the one or more arrays aligned in a second direction (D2), for example vertical, have for example a 5.0 x 4.6 mm 2 cross section and have a residual induction B = 1.1 T in the vertical direction y.

Figure 5 shows a graph that represents the vertical component of the magnetic induction By on a line oriented along the direction z (D3) perpendicular to the plane of the grid (G) and passing through the opening (A) at the centre of the grid (G) (x=0, y=0). It is possible to observe the asymmetry between the upstream side (z<0) and the downstream side of the grid (G) (z>0).

Figure 6 shows a graph that represents the vertical component of the magnetic induction By on the vertical plane yz and perpendicular to the plane of the grid (G). It is possible to observe the asymmetry between the upstream side (z<0) and the downstream side of the grid (G) (z>0).

Figure 7 shows a graph that represents the intensity and direction of the component of the magnetic induction Byz on the vertical plane yz orthogonal to the plane of the grid (G). Upstream of the grid (z<0) the magnetic induction Byz is higher than downstream (z>0).

Thus the new grid (G) comprises a plurality of magnets (Ml, M2), permanent magnets or electromagnets, arranged symmetrically with respect to a surface (S) and aligned in one or more arrays according to at least two genetically incident directions (Dl) and (D2), so as to form said grid (G) with regularly arranged openings (A), which allow the passage of particles, gases or other fluids through said surface (S).

In the simplest embodiment of the invention, said grid (G) comprises at least two arrays of magnets (Ml) aligned in a first direction (Dl), wherein two or more magnets (M2) are interposed between said two arrays of magnets (Ml) so as to define said grid (G) with openings (A).

Said magnets (Ml) forming part of said arrays aligned in said first direction (Dl) are magnetized in a direction perpendicular to said surface S, while said interposed magnets (M2) are magnetized in a direction parallel to the surface S.

The magnetic field produced by said grid (G) of magnets (Ml, M2) has an asymmetrical configuration with respect to said surface (S), so that the magnetic field on one side of the surface (S) is more intense compared to the magnetic field on the other side of the same surface (S).

In general, said grid (G) of magnets (Ml, M2) comprises n arrays of magnets (Ml) aligned in said first direction (Dl) and n-1 arrays of magnets (M2) aligned in said second direction (D2), wherein each of the magnets (M2) aligned in said second direction (D2) is interposed between two consecutive arrays of magnets (Ml) aligned in said first direction.

As shown in Figures 1, 2, 3a and 3b, said magnets (Ml) forming part of said arrays geometrically aligned according to said first direction (Dl) are magnetized in an alternate manner on successive arrays. Similarly, said magnets (M2) forming part of the arrays geometrically aligned according to said second direction (D2) are magnetized in an alternate manner on successive arrays.

Tests carried out

1. Numerical simulation of the magnetic configuration, calculated according to the arrangement, geometry, and material properties of the permanent magnets, solving the fundamental equations of electromagnetism by means of an integral method.

2. Construction of a prototype. The prototype consists of magnets arranged in a grid lying on a plane surface. The magnets are held in position by a copper structure having the form of a grid, obtained by electrodeposition. The structure is equipped with slots for the insertion and containment of the magnets in the expected position and with circular openings for the passage of particles or fluids through the grid. The size of the circular openings also allows the insertion of a magnetic field sensor through the grid.

3. Experimental characterization of the magnetic configuration generated by the prototype by scanning the magnetic field at regular intervals along paths which are straight, parallel and transverse to the plane of the grid, using a gaussmeter with a Hall effect sensor.

4. The experimental results and the numerical simulations are very similar. Therefore, with reference to the description provided above and the attached tables, the following claims are expressed.

Bibliography

[1] K. Halbach: "Fields and first order perturbation effects in two- dimensional conductor dominated magnets", Nucl. Instruments and Methods, 78 (1970) 185-198.

[2] J. C. Mallison: "One-sided fluxes - A magnetic curiosity?", IEEE Transactions on Magnetics, Vol. 9, No. 4, Dec. 1973, 678- 682.

[3] K. Halbach: "Design of permanent multipole magnets with oriented rare earth cobalt material", Nucl. Intruments and Methods, 169 (1980) 1-10.

[4] S. M. Lund, K. Halbach: "Iron-free permanent magnet systems for charged particle beam optics", Fusion Engineering and Design, 32-33 (1996) 401-415.

[5] F. Bloch, O. Cugat, G. Meunier, J. C. Toussaint: "Innovating approaches to the generation of intense magnetic fields: Design and optimization of a 4 Tesla permanent magnets flux source", IEEE Transactions on Magnetics, Vol. 34, No. 5, Sept. 1998, 2465- 2468.

[6] P. Suominen, O. Tarvainen, H. Koivisto: "3D-simulation studies of the modified magnetic multipole structure for an electron cyclotron resonance ion source", Nucl. Instruments and Method sub Physics Research B, 225 (2004) 572-578.

[7] J. E. Hilton, S. M. McMurry: "An adjustable linear Halbach array", Journal of Magnetism and magnetic Materials, 324 (2012) 2051-2056.

[8] P. Jin, S. Fang, H. Lin, X. Wang, S. Zhou: "A novel linear and rotary Halbach permanent magnet actuator with two degrees of freedom", Journal of Applied Physics, 111 (2012), 07E725 - 07E725-3.

[9] K. Menzel, C. W. Windt, J. A. Lindner, A. Michel, H. Nirschl: "Dipolar openable Halbach magnet design for high-gradient magnetic filtration", Separation and Purification Technology, 105 (2013) 114-120.