Patent Document

CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    This is a non-provisional application which claims the benefit of an earlier-filed provisional application pursuant to 37 C.F.R. §1.53( c). The earlier application was filed on Mar. 29, 2002, and was assigned Serial No. 60/368,349. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002] This invention was developed at the National High Magnetic Field Laboratory in Tallahassee, Fla. The research and development has been federally sponsored. 
     
    
     
       MICROFICHE APPENDIX  
         [0003]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention.  
           [0005]    This invention relates to the field of electromagnets. More specifically, the invention comprises a tilted Bitter-disk type magnet capable of producing a uniform field which is transverse to the center axis of the coil.  
           [0006]    2. Description of the Related Art.  
           [0007]    Bitter-disk type electromagnets have been in use for many decades. While it is true that those skilled in the art are familiar with their design and construction, a brief explanation of the prior art will be helpful in understanding the proposed invention.  
           [0008]    [0008]FIG. 1 shows a prior art Bitter-disk magnet. End plate  12  is the anchoring point for a number of radially-spaced tie rods  16 . In practice tie rods  16  have uniform length. Some of these are shown cut away in order to aid visualization of other components. A Bitter-disk magnet is typically constructed by stacking the components. Starting with end plate  12 , tie rods  16  are added. A series of conducting disks  18  are then slipped onto tie rods  16 . The reader will observe that each conducting disk  18  has a series of holes designed to accommodate tie rods  16 . Conducting disks  18  are made of thin conductive material, such as copper or aluminum.  
           [0009]    Turning briefly to FIG. 2, the reader may observe conducting disk  18  in more detail. Tie rod holes  24  are uniformly spaced around its perimeter. Cooling holes  26  are also spaced about conducting disk  18 . These holes are sometimes made as elongated slots in more complex patterns to optimize both cooling and mechanical strength. As they are not important features of the present invention, however, they have been illustrated simply. In order to avoid visual clutter, the cooling holes have not been illustrated at all in FIG. 1.  
           [0010]    [0010]FIG. 2 shows cut  22  in conducting disk  18 . This is a radial cut extending completely through one side of the disk. The reader will observe that the two sides of the disk have been displaced vertically, with the result that conducting disk  18  forms one turn of a helix having a shallow pitch. Upper side  62  of cut  22  is higher than lower side  60 . The importance of this fact will become apparent as the construction of the device is explained further.  
           [0011]    Prior art Bitter magnets are made in several different ways. The specifics of the prior art construction techniques are not critical to the present invention, since the present invention could be constructed using any of the prior art techniques. However, in order to aid the understanding of those not skilled in the art, one of the prior art construction techniques will be discussed in detail:  
           [0012]    Returning now to FIG. 1, the reader will observe that six conducting disks  18  are initially placed over tie rods  16  (the lowest part of the stack in the view). As they are stacked, each successive disk is indexed {fraction (1/15)} turn in the clockwise direction (corresponding to the fact that there are 15 tie rods  16 ). Turning to FIG. 3, the effect of the rotational indexing may be more readily observed. Six conducting disks  18  have been assembled to create conductor stack  30 . Conducting disks  18  have also been “nested” together. The {fraction (1/15)} turn is an arbitrary figure—corresponding to the use of 15 tie rods. If  16  tie rods were used, the appropriate index could be {fraction (1/16)} turn. Rotational indexing as large as ⅓ turn is in common use, especially for smaller diameter stacks.  
           [0013]    The disks are nested in the manner shown, so that upper side  62  of one conductor disk  18  lies over upper side  62  of the conductor disk  18  just below it. The disks in FIG. 3 are shown with a significant gap between them. The Bitter-disk assembly method squeezes the disks tightly together when the device is complete. When squeezed together, conducting disks  18  form one integral conductor having a helical shape—albeit with a very shallow pitch. Conductor stack  30  then forms a portion of one turn of the Bitter-disk magnet.  
           [0014]    Returning now to FIG. 1, the description of the prior art device will be continued. The reader will observe that four conductor stacks  30  are shown in the assembly (in the uncompressed state). In reality, many such conductor stacks  30  will be stacked onto tie rods  16 .  
           [0015]    The desired result is to accommodate a large electrical current flowing through a helix having a shallow pitch. The desired path of current flow commences with input conductor  64  on end plate  12  (which makes contact with the underside of the lowermost conducting disk  18 ). A second end plate  12  (not shown) will form the upper boundary of the assembly (“sandwiching” the other components in between). The current will then exit the device through a corresponding output conductor on the upper end plate  12 . Those skilled in the art will realize that if one simply stacks a number of conductor stacks  30  on the device, the electrical current will not flow in the desired helix. Rather, it will simply flow directly from the lower end plate  12  to the upper end plate  12  in a linear fashion. An additional element is required to prevent this.  
           [0016]    Insulating disks  20  are placed within each conductor stack  30  to prevent the aforementioned linear current flow. Each insulating disk  20  is made of a material having a very high electrical resistance. The dimensional features of each insulating disk  20  (tie rod holes, cooling holes, etc.) are similar to the dimensional features of conducting disks  18 . Each conductor stack  30  incorporates one insulating disk  20  nested into the stack. FIG. 1B shows a detail of this arrangement. The reader will observe the upper portion and lower portion of each insulating disk  20  (both are labeled as “20” in the view so that the reader may easily distinguish them from conducting disks  18 ). The reader will also observe how each insulating disk  20  nests into the helix formed by the six conducting disks  18 .  
           [0017]    [0017]FIG. 3 also illustrates this arrangement. Insulating disk  20  is placed immediately over the first conducting disk  18 . It then follows the same helical pattern as the conducting disk  18 . Returning now to FIG. 1, the cumulative effect of this construction will be explained. The four conductor stacks  30  shown in FIG. 1 are identical. When they are compressed together, the four insulating disks  20  will form one continuous helix through the stacked conducting disks  18 . Thus, the construction disclosed forces a helical flow of electrical current through the device.  
           [0018]    Those skilled in the art will realize that when a substantial electrical current is passed through Bitter magnet  10 , strong mechanical forces are created (Lorentz forces). Significant heat is also introduced through resistive losses. Thus, the device must be able to withstand large internal mechanical forces, and it must also be able to dissipate heat. Once the entire device is assembled with the two end plates  12  in place, the end plates are mechanically forced toward each other. The lower ends of tie rods  16  are anchored in the lower end plate  12 . The upper ends pass through holes in the upper end plate  12 . The exposed upper ends are threaded so that a set of nuts can be threaded onto the exposed ends of tie rods  16  and tightened to draw the entire assembly tightly together. In this fashion, the device is capable of resisting the Lorentz forces, which generally tend to move the disks and other components relative to each other.  
           [0019]    Because Bitter magnet  10  generates substantial heat during operation, natural convective cooling is generally inadequate. Forced convective cooling, using deionized water, oil, or liquid nitrogen is therefore employed. A sealed cooling jacket is created by providing an inner cylindrical wall bounded on its lower end by central hole  14  in the lower end plate  12 , and bounded on its lower end by central hole  14  in the upper end plate  12 . An outer cylindrical wall is provided outside the outer perimeter of the disks, extending from the lower end plate  12  to the upper end plate  12 . All the components illustrated are thereby encased in a sealed chamber. The liquid is then forced into the cooling jacket, where it flows from one end of the device to the other through the aligned cooling holes  26  in the stacked disks (the cooling holes align in the conducting and insulating disks). In FIG. 1, the cooling flow would be linear from top to bottom or bottom to top.  
           [0020]    Those skilled in the art will realize that the completed Bitter magnet  10  will generate an intense magnetic field within the cylindrical cavity within the inner cylindrical wall. Those skilled in the art will also realize that it is possible to generate an even greater magnetic field by nesting concentric Bitter-type coils. All these components are well known within the prior art.  
           [0021]    The principle limitation of the prior art Bitter-type magnets is that they can only produce a longitudinal magnetic field—aligned with the central axis of the coil. The present invention seeks to overcome this limitation through the use of a modified Bitter magnet.  
         BRIEF SUMMARY OF THE INVENTION  
         [0022]    The present invention comprises a new type of electromagnet in which the plane of each turn of the conducting coil is rotated with respect to the central axis. This results in the induced magnetic field being oriented off the central axis. A set of two such coil assemblies are preferably nested, with the current flowing in opposite directions within the two coils. This results in the components of the two induced magnetic fields lying along the center axis canceling each other out, leaving only a purely transverse magnetic field. In addition, variations in the angular offset of the nested coils can be used to create a magnetic field having almost any orientation. Three or more such nested conductor assemblies can be employed to strengthen and adjust the transverse magnetic field. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is an isometric view, showing a prior art Bitter magnet.  
         [0024]    [0024]FIG. 1B is a detail view, showing a prior art Bitter magnet.  
         [0025]    [0025]FIG. 2 is an isometric view, showing a prior art conducting disk.  
         [0026]    [0026]FIG. 3 is an isometric view, showing a prior art conductor stack.  
         [0027]    [0027]FIG. 4 is an isometric view, showing the proposed invention.  
         [0028]    [0028]FIG. 5 comprises two orthogonal views, illustrating the nature of the 45° conductor stack.  
         [0029]    [0029]FIG. 6 is an isometric view, showing the 45° conductor stack.  
         [0030]    [0030]FIG. 6B is an isometric, showing a single 45° conducting disk.  
         [0031]    [0031]FIG. 6C is a plan view, showing a single 45° conducting disk.  
         [0032]    [0032]FIG. 7 is an isometric view, showing a simplified representation of a nested pair of Bitter coils.  
         [0033]    [0033]FIG. 8 is an isometric view, showing the helical nature of the current flow through the coils shown in FIG. 7.  
         [0034]    [0034]FIG. 9 is an isometric view with a cutaway, showing the magnetic fields induced by the nested pair of Bitter coils.  
         [0035]    [0035]FIG. 10 is a plan view, showing the magnetic fields induced by the nested pair of Bitter coils.  
         [0036]    [0036]FIG. 11 is an isometric view, showing a simplified representation of four nested Bitter coils.  
         [0037]    [0037]FIG. 12 is an isometric view, showing a simplified representation of three nested Bitter coils.  
         [0038]    [0038]FIG. 13 is an isometric view, showing a pair of 20° nested coils.  
         [0039]    [0039]FIG. 14 is a plan view, showing a pair of 20° nested coils.  
         [0040]    [0040]FIG. 15A is an isometric view, showing a circular conducting disk.  
         [0041]    [0041]FIG. 15B is an isometric view, showing an angularly-offset conduct stack made from circular disks.  
         [0042]    [0042]FIG. 15C is an isometric view, showing the elliptical nature of the center bore formed by circular disks.  
         [0043]    [0043]FIG. 16 is an isometric view, showing a non-circular variant.  
         [0044]    [0044]FIG. 17 is an isometric view, showing two nested non-matched coils.  
         [0045]    [0045]FIG. 18 is an isometric view, showing how each turn of a coil lies approximately in one plane.  
         [0046]    [0046]FIG. 19 is an isometric view, showing a general representation of an angularly offset coil.  
         [0047]    REFERENCE NUMERALS IN THE DRAWINGS  
                                               10   Bitter magnet   12   end plate       14   central hole   16   tie rod       18   conducting disk   20   insulating disk       22   cut   24   tie rod hole       26   cooling hole   28   sector cut       30   conductor stack   32   angled end plate       34   45° conducting disk   36   45° conductor stack       38   projected center bore   40   projected tie rod hole       42   first Bitter coil   44   second Bitter coil       46   first coil current   48   second coil current       50   first induced field   52   second induced field       54   resultant field   56   third Bitter coil       58   fourth Bitter coil   60   lower side       62   upper side   64   input conductor       66   simplified helix   68   center axis       70   third coil current   72   fourth coil current       74   transverse field Bitter magnet       78   square disk stack   80   elliptical bore       82   theoretical turn plane   84   perpendicular plane       86   turn plane normal vector                  
 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0048]    [0048]FIG. 4 depicts one possible way to physically construct the proposed invention. Angled end plate  32  is substituted for the conventional end plate  12 . 45° conducting disks  34  are placed onto tie rods  16  in the same manner as for the prior art device (including the rotational indexing). The reader will note, however, that 45° conducting disks  34  form a current loop which is offset 45° from the center axis of transverse field Bitter magnet  74 . The six 45° conducting disks  34  combine to form 45° conductor stack  36 . A series of alternating insulating disks and 45° conductor stacks are added to 45° conductor stack  36  shown to build a laminated assembly similar to the prior art device—with one critical distinction: the current flowing through the device still flows in a helix, but the arcs within the helix the offset 45° from the center axis of the device.  
         [0049]    [0049]FIG. 5 is presented to clearly show this angular offset. The lefthand view in FIG. 5 corresponds to looking straight down on 45° conductor stack  36  from directly above the device shown in FIG. 4. The reader will note that projected center bore  38  is perfectly circular. Likewise, projected tie rod holes  40  are perfectly circular. Thus, 45° conductor stack  36  fits securely within a cooling jacket similar to the one described for the prior art device. It can also fit over tie rods  16 .  
         [0050]    The right-hand view shown in FIG. 5 corresponds to a right side view of 45° conductor stack  36 . The reader will observe that the stack forms a helix, but one which is offset 45° from center axis  68 . FIG. 6 is an isometric view showing 45° conductor stack  36 . The stack is rotationally indexed, as shown by the displacement in successive cuts  22 . Like the prior art device, tie rod holes  24  in successive 45° conducting disks align. Cooling holes are also present in these disks, and they also align. For purposes of visual simplicity, they have not been illustrated.  
         [0051]    [0051]FIG. 6B shows a single 45° conducting disk  34 . Its features are generally similar to those found in the prior art device, including the cut producing a shallow helical shape. However, as those skilled in the art will appreciate, 45° conducting disk  34  does not have a circular shape. FIG. 6C shows a 45° conducting disk  34  in a plan view. The reader will observe that both its inner and outer perimeters have an elliptical shape. This shape is used, so that when the disk is tilted 45° in its installation, the inner and outer perimeters will project along the center bore of the Bitter magnet as pure circles. If a disk shape other than elliptical is used, the inner and outer perimeters will project as something other than a pure circle.  
         [0052]    All of the preceding description has been presented so that the reader may: (1) understand the construction of Bitter-type magnets; and (2) understand how the current flow in such a magnet can be forced to assume a path which is angularly offset from the center axis of the magnet. These principles will now be employed to describe some of the novel features of the present invention.  
         [0053]    [0053]FIG. 7 depicts a nested pair of transverse field Bitter coils. Second Bitter coil  44  fits around first Bitter coil  42 . Both coils are shown as simplified representations. The reader should understand that to physically realize these coils would require the type of structures disclosed in FIGS.  4 - 6 . However, for the present purposes, it is sufficient to understand that the current path in each of these coils follows an angularly offset helix. In other words, although the coils are depicted as solid objects, they are in fact comprised of stacks of 45° conducting disks  34 . FIG. 8 depicts the nature of the current path in first Bitter coil  42 —indicated as simplified helix  66 .  
         [0054]    [0054]FIG. 9 shows the nested pair with a cutaway to aid visualization. First Bitter coil  42  is energized so that first coil current  46  flows in a counterclockwise direction (when viewed down center axis  68  from the left hand side). Of course, the reader should recall that the current loops within Bitter coil  42  are angularly offset 45° from center axis  68 . The result of the current flow is first induced field  50 . The direction of first induced field  50  corresponds to the current flow within first Bitter coil  42 , according to the right-hand rule.  
         [0055]    Second Bitter coil  44  is energized so that second coil current  48  flows in a clockwise direction when viewed down center axis  68  from the left hand side. The result of second coil current  48  is second induced field  52 . The orientation of second induced field  52  is angularly displaced 90° from first induced field  50 , via application of the right-hand rule.  
         [0056]    [0056]FIG. 10 shows the same assembly in a plan view. Those skilled in the art will realize that by carefully designing the structure of the two Bitter coils and carefully regulating the current flowing therein, it is possible to make the strength of first induced field  50  match the strength of second induced field  52 . When this occurs the components of first induced field  50  and second induced field  52  which lie along center axis  68  will cancel each other out. Resultant field  54  will remain, which is in an orientation that is transverse to center axis  68 . Thus, by carefully designing the nested pair of Bitter coils, it is possible to produce a magnetic field which is purely transverse to center axis  68 .  
         [0057]    Those skilled in the art will also realize that the direction of current flow within the two nested coils may be arbitrarily selected—so long as the currents in the two coils flow in opposite directions. Thus, by reversing the current flow in the two coils, it is possible to create a transverse magnetic field in either direction (straight up or straight down as viewed in FIG. 10).  
         [0058]    [0058]FIG. 11 depicts a set of four nested Bitter coils which carries the concept further. Third Bitter coil  56  and fourth Bitter coil  58  are added around the pair of Bitter coils described in FIGS. 7 through 10. Although they are again illustrated in simplified form, their structure corresponds to that shown in FIGS. 4 through 6.  
         [0059]    Third Bitter coil  56  is energized so that third coil current  70  flows in a counterclockwise direction when viewed along center axis  68  from the left hand side. Fourth Bitter coil  58  is energized so that fourth coil current  72  flows in a clockwise direction. This current flow produces additional induced fields like those illustrated in FIG. 10. By carefully designing the third and fourth Bitter coils to match each other, the components of the induced fields produced by the third and fourth Bitter coils which lie along center axis  68  will again cancel each other out. The transverse component, however, will serve to intensify the transverse magnetic field created by the first two nested Bitter coils. Thus, it is possible by nesting additional Bitter coils, to further strengthen the purely transverse magnetic field created by the first two Bitter coils. Furthermore, designs can be created wherein consecutive coils can have the same orientation and current direction.  
         [0060]    The reader should appreciate that the invention is not limited to an even numbers of nested coils. FIG. 12 shows an odd-numbered configuration. First coil current  46  and third coil current  70  flow in the same direction. Second coil current  48  flows in the opposite direction. The result of this arrangement is a field which is angularly offset from the central bore of the magnet, and which cab be aligned to any desired orientation (including 90 degrees). Using an odd number of nested coils along with variations in the current flow can produce a field having an arbitrary angular offset from the central bore. Thus, not only can the present invention produce a purely transverse field, it can also produce a field having any desired angular offset from the central bore.  
         [0061]    Likewise, although coil stacks having a 45 degree offset have been used for purposes of illustration, the invention is not limited to this type. FIG. 13 shows a pair of nested coils having a 20 degree angular offset (The top half of the coils are again cut away to aid visualization). Like the example shown in FIG. 9, first coil current  46  flows in the opposite direction of second coil current  48 . First coil current  46  creates first induced field  50 , as graphically shown by the vector arrow. Second coil current  48  creates second induced field  52 . Referring now to FIG. 14, the reader will observe that the components of the two induced fields lying along center axis  68  cancel each other out, leaving resultant field  54  (which is again purely transverse). Thus, those skilled in the art will realize that the angular offset for the coils is not critical to producing the transverse field, although it has an obvious effect on the strength of the transverse field.  
         [0062]    The previous examples have used elliptical disks so that when they are angularly offset a cylindrical bore will be produced. While such a design has its advantages, the invention can certainly be practiced using non-elliptical conductor disks. FIG. 15A shows a perfectly circular conductor disk  18  (Compare the elliptical conductor disk  18  shown in FIG. 6C). Detailed features of the disk—such as the radial slit, mounting holes, and cooling holes—have been omitted for simplicity. FIG. 5B shows a conductor stack  30  made from a series of angularly offset conductor disks  18 . Insulating and other features would be included to force a helical current flow through the stack, similar to the flow shown in FIG. 8. However, because circular disks are used, the shape created by the stack will not be cylindrical. FIG. 15C shows a view which is only slightly offset from the center bore. In this view, the reader will observe that elliptical bore  80  is formed by stacking the circular disks using the angular offset. Thus, the reader will appreciate that the invention is by no means confined to the use of elliptical disks.  
         [0063]    In fact, non-curved shapes can also be employed. FIG. 16 shows a square disk stack  78  formed by angular offsetting a stack of square conductors. The current path through this stack is again helical, but the center “bore” is rectangular.  
         [0064]    Finally, although most of the examples presented have been configured to create a purely transverse field, the invention is not limited to such a field. In some instances, it may be desirable to create a field with transverse and aligned components (where the term “aligned” means aligned with the center bore of the conductor stack). This can be accomplished via mixing different types of coils. FIG. 17 shows such a magnet, where first bitter coil  42  has a different angle of inclination that second bitter coil  44 .  
         [0065]    The magnets disclosed can also be switched to oscillate between conventional and transverse fields. Returning briefly to FIG. 13, the reader will recall that the two coils were energized using current flowing in opposite directions (first coil current  46  and second coil current  48 ). Switching means can be used to make the two coil currents flow in the same direction. By proper tuning of these currents and the coil geometry, a purely aligned field can be created. A brief look at FIG. 14 will confirm this fact to those skilled in the art. Reversing the current in second bitter coil  44  will shift the orientation of second induced field  52  by 180 degrees. The transverse components of first induced field  50  and second induced field  52  will then cancel each other out, leaving a field aligned with center axis  68 . Thus, switching the current direction in one of the coils can switch the magnet from a purely transverse field to a purely aligned one. More complicated permutations are possible with the addition of more coils. Switching the current direction in a magnet such as shown in FIG. 11, as one example, can produce a variety of combined transverse and aligned fields.  
         [0066]    The invention broadly encompasses helical coils in which each turn of the helix is angularly displaced (to 45 degrees, 30 degrees, or other desired orientation). FIG. 18 shows simplified helix  66 . Each turn of the helix lies approximately in one plane. The word “approximately” is used because, of course, a helix does not truly lie in a single plane (Observe the right view of FIG. 5). However, each turn is centered about one plane. The planes for each turn of the illustrated helix are designated as theoretical turn planes  82  in the view. The reader will observe that these planes are a series of inclined and parallel planes, each offset a fixed distance from its neighbor. These planes are inclined from center axis  68  a fixed amount.  
         [0067]    [0067]FIG. 19 shows this inclination more clearly. The leading theoretical turn plane  82  is shown. Perpendicular plane  84  is a plane which is perpendicular to center axis  68 , and which intersects center axis  68  at the same point as theoretical turn plane  82 . A prior art helical conductor would have theoretical turn planes parallel to perpendicular plane  84 . The present invention is distinguished by the fact that its turns are inclined. Turn plane normal vector  86  is perpendicular to theoretical turn plane  82 . The angle between this vector and center axis  68  represents the inclination of the inclined turns from the conventional orientation found in the prior art.  
         [0068]    Although the preceding description contains significant detail it should not be viewed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments. Accordingly, the scope of the invention should be set by the following claims rather than by the examples given.

Technology Category: 5