Abstract:
An electromagnet having at least one access port oriented perpendicularly to the electromagnet&#39;s central axis. The magnet has a conventional helical winding along its central axis. However, at some point along the length of the axis, the pitch of the helical winding is greatly increased in order to create a region with a comparatively low turn density. One or more ports are provided in this region. These ports provide access from the magnet&#39;s central bore to the magnet&#39;s exterior. A sample can be placed in the central bore near the ports. A beam traveling down the central bore, or through one of the radial ports, will strike the sample and be scattered in all directions. The ports allow access for instrumentation which is used to evaluate the scattered beam.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This is a non-provisional application claiming the benefit—pursuant to 37 C.F.R. §1.53(c) of an earlier-filed provisional application. The provisional application was filed on Mar. 10, 2006 and was assigned application Ser. No. 60/781,104. The provisional application listed the same inventors. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   This invention was developed at the National High Magnetic Field Laboratory in Tallahassee, Fla., U.S.A. The research and development has been federally sponsored. 

   MICROFICHE APPENDIX 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to the field of electromagnets. More specifically, the invention comprises a resistive magnet with radial ports providing access to the central region. 
   2. Description of the Related Art 
   The present invention proposes to create an electromagnet having a split at the mid-plane in order to allow clear radial access to the magnet&#39;s core. Several approaches may be useful for constructing such a magnet. It is therefore important for the reader to understand some known techniques for electromagnet construction prior to receiving the description of the present invention. 
   A good discussion of prior art construction techniques for high-field resistive magnets is found in an article written by one of the present inventors: Mark D. Bird, “Resistive Magnet Technology for Hybrid Inserts,”  Superconductor Science and Technology , vol. 17, 2004, pp. R19-R33. Discussions of prior art construction techniques for high-field split resistive magnets are found in two articles published in the  IEEE Transactions on Magnetics : Robert J. Weggel and M. J. Leupold, “A 17.5-Tesla Magnet with Multiple Radial Access Ports,” vol. 24, no. 2, March 1988, pp. 1390-1392; and Pierre Rub and G. Maret. “A New 18-T Resistive magnet with Radial Bores,” vol. 30, no. 4, July 1994, pp. 2158-2161. 
   The basic principle of an electromagnet is that a conductor must be wrapped around a central bore for one or more turns. Many turns are typically used.  FIG. 1  shows an electromagnet created by wrapping conductor  100  around central bore  104  in a helical path. The two ends of the helical path may be provided with a flat  30  to facilitate mounting the coil. Helical gap  28  is typically filled with an insulator of some sort to ensure that the current flows through the helical path. 
   The version shown in  FIG. 1  does not show any cooling channels. For the conductor to carry large currents, cooling channels would need to be added. Radial cooling channels can be cut using wire EDM to make a “Monohelix” magnet as described by Weggel in “The Monohelix: 1) Five Years of Operation at the Francis Bitter National Magnet Laboratory” and 2) Finite Element Stress Analysis,”  IEEE Trans. on Magn. , vol. 28, no. 1, January 1992. In the alternative, axial cooling channels can be cut via micro-hole and wire EDM to make a Florida-Helix as described by one of the present inventors, Mark D. Bird, in “Florida-Helix Resistive Magnets,”  IEEE Trans. on Applied Supercond. , vol. 14, no. 2, 2004, pps. 1271-1275. As a Florida-helix is a recent development, the drawing figures depicting it are not described as “prior art.” 
   The electrical current passing through the helix during operation generates Lorentz forces and considerable heat. Other components are needed to accommodate these factors. The whole device is placed within a surrounding jacket, so that a pressurized fluid can be pumped through the cooling channels. Mechanical attachment features are generally also provided. For purposes of visual clarity, these features have been omitted in  FIG. 1 . 
   Bitter-disk type electromagnets are another known approach to carrying high currents. While it is true that those skilled in the art are familiar with the design and construction of such magnets, a brief explanation of the prior art may be helpful.  FIG. 2  shows a prior art Bitter-disk magnet. End plate  40  is the anchoring point for a number of circumferentially-spaced tie rods  44 . In practice tie rods  44  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  40 , tie rods  44  are added. A series of conducting disks  36  are then slipped onto tie rods  44 . The reader will observe that each conducting disk  36  has a series of holes designed to accommodate tie rods  44 . Conducting disks  36  are made of thin conductive material, such as copper or aluminum. 
   Turning briefly to  FIG. 4 , the reader may observe conducting disk  36  in more detail. Tie rod holes  46  are uniformly spaced around its perimeter. Cooling holes  54  are also uniformly spaced about conducting disk  36 . Cut  52  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  36  forms one turn of a helix having a shallow pitch. Upper side  50  of cut  52  is higher than lower side  48 . The importance of this fact will become apparent as the construction of the device is explained further. 
   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 employ Bitter stacks 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. 
   Returning now to  FIG. 2 , the reader will observe that six conducting disks  36  are initially placed over tie rods  44  (the lowest part of the stack in the view). For the specific version shown, as each conductive disk is stacked, it is indexed 1/15 turn in the clockwise direction (corresponding to the fact that there are  15  tie rods  44 ). Turning to  FIG. 5 , the effect of the rotational indexing may be more readily observed. 
   Six conducting disks  36  have been assembled to create one conductor turn  42 . Conducting disks  36  have also been “nested” together. The 1/15 turn is a somewhat arbitrary figure. They could be indexed in other increments. Rotational indexing as large as ⅓ turn is in common use, especially for smaller diameter stacks. In fact, it is more customary to divide the 360 degrees found in one complete turn into even increments. If six stacked conductors are used to make one turn, then it would be common to rotationally index each disk ⅙ turn over its predecessor (60 degree index per disk). 
   The disks are nested in the manner shown, so that upper side  50  of one conductor disk  36  lies over upper side  50  of the conductor disk  36  just below it. The disks in  FIG. 2  are shown with a significant gap between them. The Bitter-disk assembly method squeezes the disks tightly together when the device is complete. The squeezing is typically accomplished by threading the ends of the tie rods. Rigid end plates are slipped over the tie rods at the top and bottom of the stack. Nuts are then threaded onto the exposed ends of the tie rods and tightened to squeeze the end plates toward each other. When squeezed together, conducting disks  36  form one integral conductor having a helical path—albeit with a very shallow pitch. 
   Still looking at  FIG. 2 , the description of the prior art device will be continued. The reader will observe that four conductor turns  42  are shown in the assembly (in the uncompressed state). In reality, many such conductor turns  42  will be stacked onto tie rods  44 . 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 one end plate  40  (which makes contact with the underside of the lowermost conducting disk  36 ). A second end plate  40  (not shown) will form the upper boundary of the assembly (“sandwiching” the other components in between). The current will then exit the device through the upper end plate  40  (The tie rods are electrically isolated from the end plates and the disks so that they will carry no current). Those skilled in the art will realize that if one simply stacks a number of conductor turns  42  on the device, the electrical current will not flow in the desired helix. Rather, it will simply flow directly from the lower end plate  40  to the upper end plate  40  in a linear fashion. An additional element is required to prevent this. 
   Insulating disks  34  are placed within each conductor turn  42  to prevent the aforementioned linear current flow. Each insulating disk  34  is made of a material having a very high electrical resistance. The dimensional features of each insulating disk  34  (tie rod holes, cooling holes, etc.) are similar to the dimensional features of conducting disks  36 . Each conductor turn  42  incorporates at least one insulating disk  34  nested into the stack.  FIG. 3  shows a detail of this arrangement. The reader will observe the upper portion and lower portion of each insulating disk  34  (both ends of each disk are labeled as “34” in the view so that the reader may easily distinguish them from conducting disks  36 ). The reader will also observe how each insulating disk  34  nests into the helix formed by the six conducting disks  36 . 
     FIG. 5  also illustrates this arrangement. Insulating disk  20  is placed immediately over the first conducting disk  36 . It then follows the same helical pattern as the conducting disk  36 . Returning now to  FIG. 2 , the cumulative effect of this construction will be explained. The four conductor turns  42  shown in  FIG. 2  are identical. When they are compressed together, the four insulating disks  34  will force the current to flow through one continuous helix through the stacked conducting disks  36 . Thus, the construction disclosed forces a helical flow of electrical current through the device. An actual Bitter magnet might include 20 or more such conductor turns. 
   Those skilled in the art will realize that when a substantial electrical current is passed through Bitter magnet  32 , 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  40  in place, the end plates are mechanically forced toward each other. The lower ends of tie rods  44  are attached to the lower end plate  40 . The upper ends typically pass through holes in the upper end plate  40 . The exposed upper ends are threaded so that a set of nuts can be threaded onto the exposed ends of tie rods  44  and tightened to draw the entire assembly tightly together. In this fashion, the device is capable of resisting the Lorentz forces, which tend to move the disks and other components relative to each other. Not all Bitter-type magnets use tie rods. Other mechanical structures can be used to align the components and resist the Lorentz forces. However, since tie rods are the most common approach, they have been illustrated. 
   Because Bitter magnet  32  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 the lower end plate  40 , and bounded on its upper end by the upper end plate  42 . An outer cylindrical wall is provided outside the outer perimeter of the disks, extending from the lower end plate  42  to the upper end plate  42 . All the components illustrated are thereby encased in a sealed chamber. The cooling 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 in the stacked disks (the cooling holes align in the conducting and insulating disks). In  FIG. 2 , the cooling flow would typically be linear from top to bottom or bottom to top. 
   Those skilled in the art will realize that the completed Bitter magnet  32  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 of high-field resistive magnet construction. However, the reader should be aware that the history of high-field split magnet construction is much more limited, with only a few magnets having been built. Most of these were built by Weggel and Rub. In both those cases, radial access ports are provided by “interrupting” the Bitter coil at the mid-plane and introducing a copper or brass “mid-plate” that includes the access ports along with the water channels. 
   The conducting disk shown in  FIG. 4  uses round tie rod holes and round cooling holes. Any discontinuity in the cross section of the disk causes structural weakness and imperfections in the magnetic field produced. Viewed only from the standpoint of electromagnetic efficiency, the disk would ideally have no holes at all. Such a design would be impractical, however, since it could not be effectively cooled. The lack of tie rods would also prevent the disks being effectively aligned and clamped together in order to resist Lorentz forces. Thus, the design of a Bitter-type magnet inherently involves compromises between purity of the magnetic field, conductivity, mechanical strength, cooling, and other factors. 
   In recent years the traditional Bitter disk design has been improved to remedy some of its shortcomings.  FIG. 6  shows a conducting disk developed at the National High Magnetic Field Laboratory in Tallahassee, Fla., U.S.A. This type of disk is now known as a Florida-Bitter disk. 
   As the tie rods are loaded primarily in tension, a non-round shape can be used. An elongated cross section for the tie rod provides a better compromise between the strength required and the space consumed. Such tie rods are now used. Florida-Bitter disk  56  has elongated tie rod holes  58  to accommodate the modified cross section of the tie rods. The shape of the tie rods conform to the shape of the holes illustrated. 
   Elongated cooling holes also provide a more advantageous strength versus cooling compromise. Florida-Bitter disk  56  has cooling slots  60  in place of the conventional cooling holes. A series of such cooling slots are placed in concentric rings across the width of the disk. 
     FIG. 7  shows a detailed view of a portion of Florida-Bitter disk  56 , wherein these features can be seen more clearly. The reader will observe that successive circumferential arrays of cooling slots are staggered. If one starts with the innermost array of slots, the next outward array is staggered so that the slots in that array are outboard of the webs (the solid material between the slots) in the preceding array. This staggering of the cooling channels substantially enhances the mechanical strength of the conductor allowing higher fields to be attained. It is an important feature of the Florida-Bitter disk. 
   From these descriptions, the reader will gain some understanding of the construction of high-field resistive magnets. All these techniques can potentially be used in constructing a magnet according to the present invention, which contemplates providing radial access ports which are approximately perpendicular to the central axis running through the magnet&#39;s core. 
   The inclusion of a radial access port is known within the art. Technical articles have described such designs, including: R. J. Weggel, M. J. Leupold, “A 17-Tesla Magnet with Multiple Radial Access Ports”,  IEEE Transactions on Magnetics , Vol. 24, No. 2, March 1988; and P. Rub, G. Maret, “A New 18 T Resistive Magnet with Radial Bores”,  High Magnetic Field laboratory , Grenoble, France. 
   Prior art radial port designs have focused on Bitter stacks using radial cooling, meaning that the cooling flows from the central bore out to the magnet&#39;s perimeter (rather than longitudinal cooling in a direction parallel to the magnet&#39;s central axis). Some type of spacer plate is typically added in the magnet&#39;s mid-plane.  FIG. 20  shows two spacer plates  106 . Each has a pair of radial access grooves  108 . Each also has an array of radial cooling channels  110 . When the two spacer plates shown are forced together and sealed within suitable cooling fluid manifolds, the two radial access grooves provide access to the magnet&#39;s core in the transverse direction. 
     FIG. 20  shows a very simplified incarnation of this concept. The spacer plates are clamped in the middle of stacks of Bitter disks. The Bitter disks typically have etched radial cooling passages. Those skilled in the art will readily appreciate how the use of radial cooling passages facilitates the inclusion of radial access ports, since the cooling passages and the access ports both proceed from the magnet&#39;s core to its perimeter. The present invention seeks to add radial access ports to a coil using longitudinal cooling. A different approach is therefore needed. 
   Those skilled in the art will realize that the spacer plate shown in  FIG. 20  does not allow helical flow of the electrical current. It is simply an electrical “shunt” which passes the current from the Bitter stack clamped on the top of the spacers to the Bitter stack clamped on the bottom of he spacers. This current—which would flow from top to bottom in the orientation shown in the view—does not contribute to creating a magnetic field in central bore  104 . Thus, the design shown in  FIG. 20  sacrifices some field strength. The reader may naturally wish to know the significance of this sacrifice, since the relatively brief interruption in the helical current path caused by the inclusion of the spacer plates may not be intuitively significant. 
     FIG. 21  is a cross section through ¼ of a Bitter-type resistive magnet. Only the upper right quadrant is shown. The cross section is of course symmetric about the X axis (labeled as “RADIUS” in the view) and the Z axis (which correspond to the central axis of the magnet). Thus, the X axis shown in the view is the magnet&#39; mid plane. If spacers such as shown in  FIG. 20  are used, they will be placed on the X axis in the view. 
   The figure depicts the winding of a  30  Tesla magnet, using three concentric Bitter coils (first Bitter coil  80 , second Bitter coil  82 , and third Bitter coil  84 ). The Bitter coils are divided into regions. The contribution of each region—stated in Teslas per Megawatt—is then shown for each region. As an example, the region of first Bitter coil  80  actually lying next to the magnet&#39;s mid-plane, contributes 7.24 T/MW. From even a cursory inspection of this figure, one can conclude that the contribution of conductive turns lying near the magnet&#39;s mid-plane to the overall magnetic field produced is substantial. Thus, any sacrifice of turns in this area has a large impact. This fact represents a crucial disadvantage of the approach shown n  FIG. 20 . Thus, a new construction which can provide access ports through the mid plane while retaining the helical current path would be desirable. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention comprises an electromagnet having radial access ports near its mid-plane. The magnet has a conventional helical winding along a central axis. However, at some point along the length of the axis, the pitch of the helical winding is greatly increased in order to create a region with a comparatively low turn density. One or more radial ports are provided in this region. These ports provide access from the magnet&#39;s central bore to the magnet&#39;s exterior. 
   In a first type of experiment, a sample can be placed in the central bore near the ports. A beam traveling down the central bore, or through one of the radial ports, will strike the sample and be scattered in all directions. The ports allow access for instrumentation which is used to evaluate the scattered beam. 
   In a second type of experiment, a sample can be installed via one of the radial ports and then rotated while the high magnetic field is maintained. Such a technique would be used to measure the variance of the material&#39;s properties as it is rotated into different orientations (anisotropy). 
   The magnet can be created using two or more nested coils. The interior coil or coils are preferably constructed as Florida helices stacked with Florida Bitter disks. The outer coil or coils are preferably constructed as interrupted Bitter coils. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a perspective view, showing a conductive helix. 
       FIG. 2  is a perspective view, showing a prior art Bitter-disk magnet. 
       FIG. 3  is a detail view, showing a portion of a Bitter-disk magnet. 
       FIG. 4  is a perspective view, showing a prior art Bitter-disk. 
       FIG. 5  is a perspective view, showing a prior art Bitter-type conductor turn. 
       FIG. 6  is a perspective view, showing a prior art Florida-Bitter disk. 
       FIG. 7  is a detail view, showing a portion of a Florida-Bitter disk. 
       FIG. 8  is a perspective view, showing a split Florida-helix. 
       FIG. 9  is a section view, showing internal details of the embodiment of  FIG. 8 . 
       FIG. 10  is an elevation view, showing the winding pitch of the embodiment of  FIG. 8 . 
       FIG. 11  is a perspective view, showing an elliptical port in a split Florida-helix. 
       FIG. 12  is a section view, showing internal details of the embodiment of  FIG. 11 . 
       FIG. 13  is a perspective view, showing winding pitch variation in a split Florida-helix. 
       FIG. 14  is a perspective view, showing how a split Florida-helix can be divided into two halves. 
       FIG. 15  is a hidden-line perspective view, showing a housing configured to allow coolant flow around the ports in a split Florida-helix. 
       FIG. 16  is a perspective view, showing the assembly of the two halves together in the housing. 
       FIG. 17  is a perspective view, showing the completion of the assembly of  FIG. 16 . 
       FIG. 18  is a perspective view, showing the addition of Florida-Bitter disk stacks to the assembly of  FIG. 17 . 
       FIG. 19  is a sectioned perspective view, showing a representative multi-coil magnet constructed of nested Florida-helix and Florida-Bitter coils. 
       FIG. 20  is a perspective view, showing a prior art approach to the creation of access ports. 
       FIG. 21  is a graphical view, showing the contribution of the regions of an electromagnet to maximum field strength in the magnet&#39;s core. 
       FIG. 22  is a perspective view, showing a split Florida-helix with the addition of elongated tie rod holes. 
       FIG. 23  is a detailed perspective view, showing a split Florida-helix with alterations made to optimize the interface surfaces. 
       FIG. 24  is a detailed perspective view, showing the use of angled cooling slot walls near the interface surfaces. 
       FIG. 25  is a sectioned perspective view, showing a representative multi-coil magnet constructed of nested Florida-helix and Florida-Bitter coils, and the coolant flow around the access ports. 
       FIG. 26  is a perspective view with a cutaway, showing the geometry around a radial access port. 
       FIG. 27  is a detailed elevation view of  FIG. 26 , showing how coolant lows through a gap around each radial access port. 
   

   REFERENCE NUMERALS IN THE DRAWINGS 
   
     
       
             
             
             
             
           
         
             
                 
             
           
           
             
               10 
               split Florida-helix 
               12 
               port 
             
             
               14 
               shallow pitch region 
               16 
               steep pitch region 
             
             
               18 
               elliptical port 
               20 
               upper half split 
             
             
                 
                 
                 
               Florida-helix 
             
             
               22 
               lower half split Florida-helix 
               24 
               interface surface 
             
             
               26 
               Florida helix 
               28 
               helical gap 
             
             
               30 
               flat 
               32 
               Bitter magnet 
             
             
               34 
               insulating disk 
               36 
               conducting disk 
             
             
               40 
               end plate 
               42 
               conductor turn 
             
             
               44 
               tie rod 
               46 
               tie rod hole 
             
             
               48 
               lower side 
               50 
               upper side 
             
             
               52 
               cut 
               54 
               cooling hole 
             
             
               56 
               Florida-Bitter disk 
               58 
               elongated tie rod hole 
             
             
               60 
               cooling slot 
               62 
               housing 
             
             
               64 
               outer wall 
               66 
               inner housing 
             
             
               68 
               elliptical port bounding wall 
               70 
               inner port boundary 
             
             
               72 
               outer port boundary 
               74 
               split Florida-helix assembly 
             
             
               76 
               Florida-Bitter disk stack 
               78 
               spacer 
             
             
               80 
               first Bitter coil 
               82 
               second Bitter coil 
             
             
               84 
               third Bitter coil 
               86 
               fourth Bitter coil 
             
             
               88 
               outer housing 
               90 
               inner housing 
             
             
               92 
               end cap 
               94 
               cooling inlet 
             
             
               96 
               cooling outlet 
               100 
               conductor 
             
             
               104 
               central bore 
               106 
               spacer plate 
             
             
               108 
               radial access groove 
               110 
               radial cooling channel 
             
             
               112 
               modified cooling slot 
               114 
               stabilizing pin receiver 
             
             
               116 
               straight slot wall 
               118 
               angled slot wall 
             
             
               120 
               coolant 
               122 
               coolant flow gap 
             
             
               124 
               port mid point 
               126 
               port boundary 
             
             
               128 
               port relief surface 
             
             
                 
             
           
        
       
     
   
   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is a resistive magnet having access ports proximate its mid-plane. The reader will recall that  FIG. 1  shows a helix. Such a coil can be modified to create a split near its mid plane in order to allow for radial access ports.  FIG. 8  shows a Florida-helix incorporating this modification (denoted as split Florida-helix  10 ). It incorporates a helically wrapped conductor  100  around a central bore  104 . Flats  30  are preferably provided on either end. Cooling slots  60  are also provided, in a configuration similar to that shown for the Florida-Bitter disk in  FIGS. 6 and 7 . In actuality, the cooling slots may be smaller and more numerous. Larger slots are shown for purposes of visual clarity. 
   As for the conventional Florida-helix, the embodiment shown in  FIG. 8  can be created by cutting a helically-wound gap  28  through a cylindrical “blank.” The gap is typically cut using a wire EDM process. Four ports  12 —radially arrayed at 90 degree increments—are cut from the coil&#39;s exterior into central bore  104 . The ports diverge as one proceeds away from the coil&#39;s central axis. In other words, they grow wider proceeding towards the coil&#39;s exterior. This allows a more free path for emissions coming from a sample located in the coil&#39;s bore. The reader should note that the choice of four ports is somewhat arbitrary. Two, three, six, eight, or even twelve ports could be included. 
   Although the use of diverging ports is preferred for some applications, straight ports (which may be easier to manufacture) could also be used. The reader will observe that in the vicinity of these ports (whether diverging or not), the pitch of the helical gap is altered.  FIG. 9  better illustrates this feature. In  FIG. 9 , the split Florida-helix has been sectioned in half through two of the ports  12 . In the upper and lower portions of the coil the pitch of the helical gap  28  is constant and relatively shallow (shallow pitch regions  14 ). However, in the middle portion, the pitch of the helical gap is significantly increased (steep pitch region  16 ). 
     FIG. 10  shows an elevation view of the coil, rotated to better display the pitch of the helical gap through steep pitch region  16 . The helical gap remains continuous. For the specific embodiment shown, the helical gap travels through a shallow pitch, then transitions to a steep pitch, then transitions back to a shallow pitch. The transition between the shallow pitch (high current density) region  14  and the steep pitch (low current density) region  16  can be made via a continuous pitch change or via multiple pitch steps reaching over more or less than one turn. In the fairly simple version of  FIG. 10 , the current flows through the middle region in approximately one turn. The steep pitch allows the inclusion of the ports without creating a reduced cross section for current flow. 
   As illustrated, the helical gap passes through only one port. This is not the only way to fabricate the device. It is also possible to have the helical gap stop at one of the ports, then be offset, and resume at another port. The current path would obviously be altered, but the operating principles of the device are the same. 
   As for the prior Bitter-type magnets, an insulator must be inserted within the helical gap in order to ensure that the electrical current does not short in the direction of the central axis. The insulator, which may be comprised of one piece or many pieces, will occupy helical gap  28 . It must incorporate cooling slots which align with those within the split Florida-helix. If tie rod holes are included within the split Florida-helix, then the insulator will have to incorporate aligning tie rod holes as well. 
   The inclusion of the radial ports assists in conducting experiments. In a first type of experiment, a sample will typically be placed in the center of the magnet&#39;s core, proximate the ports. A beam will then be directed in one end of the magnet, through central bore  104 . The beam will strike the sample, and emissions will then radiate in all directions. Ports  12  can be further optimized to provide better visibility for instruments designed to detect the emissions. In a second type of experiment, a sample can be installed via one of the radial ports and then rotated while the high magnetic field is maintained. Such a technique would be used to measure variations according to the rotation, thereby providing data on anisotropic properties of the sample. 
     FIG. 11  shows a split Florida-helix incorporating a refined version of the access ports. Elliptical ports  18  diverge in two directions—as depicted by the sets of arrows. This double divergence allows more of the sample emissions to escape and thereby encounter the detecting instruments. 
     FIG. 12  shows a section view through the embodiment having elliptical ports  18 . The other features are the same as the embodiment shown in  FIGS. 8 through 10 . The same shallow and steep pitch regions are present. The electrical path still makes approximately one turn through the region of the ports. 
   The embodiments shown in  FIGS. 8 through 12  illustrate the main features of the split Florida-helix in an uncluttered fashion. However, actual magnet designs would typically incorporate many more turns.  FIG. 13  shows a more realistic design. Shallow pitch region  14  includes a more shallow pitch for helical gap  28  and—consequently—many more conductor turns. Approximately the same steep pitch is used for steep pitch region  16 . 
   From the description of the prior art, the reader will realize that an encompassing cooling jacket is needed to surround the split Florida-helix and force coolant to flow through the coolant slots. The existence of the ports creates a problem. The ports must be open to the magnet&#39;s exterior. However, if no liquid-tight barrier is placed within the ports, the coolant will escape. A tapered elliptical wall must therefore be placed inside elliptical ports  18 . These walls must be joined to an internal wall passing through the coil&#39;s central bore. Likewise, they must be joined to an external cylindrical wall surrounding the coil&#39;s exterior. Practical manufacturing problems are immediately apparent, since joining such walls around the split Florida-helix will be very difficult. 
     FIG. 14  presents a solution to this problem. The split Florida-helix is divided into an upper and lower half. In the view these are designated as upper half split Florida-helix  20  and lower half split Florida-helix  22 . Each half has four interface surfaces  24 . If the two halves are clamped together, current will flow from one half to the other through these surfaces. 
   The actual splitting can be done by using a thin wire EDM to saw the whole version of  FIG. 13  in half. It is also possible to make the two halves separately. Computer controlled EDM operations allow significant accuracy, so that the two halves will mate when they are brought together. 
   Dividing the coil into two halves provides a manufacturing advantage.  FIG. 15  shows housing  62 , which is configured to house the split Florida-helix. Inner wall  66  and outer wall  64  are joined by four elliptical port bounding walls  68 . Each bounding wall terminates at an inner port boundary  70  on its inner extreme and an outer port boundary  72  on its outer extreme. Thus, the housing provides four passages from its exterior to its interior. The elliptical port bounding walls may be sized to allow a slight gap between themselves and the elliptical ports, in order to allow coolant to flow around the bounding walls (which will be described in more detail subsequently). Housing  62  can be made by many conventional methods, including casting the unit as an integral piece and fabrication as a weldment of smaller pieces. 
     FIG. 16  illustrates the effective combination of housing  62  and the two halves of the split Florida-helix. Upper half split Florida-helix  20  is lowered into the housing from the top, while lower half split Florida-helix  22  is lifted into the housing from the bottom (or the housing may be lowered onto the lower half).  FIG. 17  shows the completed split Florida-helix assembly  74 . 
   If a coolant feed manifold is placed over the top of the housing and a coolant collection manifold is placed over the bottom, then pressurized coolant can be fed through the cooling slots to cool the coil. The elliptical ports still provide access to the coil&#39;s interior, without compromising the fluid seal. 
   Of course, the use of the split Florida-helix is particularly advantageous around the ports. Away from the ports, other methods can be used. As one example, Florida-Bitter stacks could be placed above and below split Florida-helix  74  to continue the helical current path over a longer distance.  FIG. 18  shows this embodiment, with two Florida-Bitter disk stacks  76  in position and ready to be clamped to the assembly. Many such stacks could be added. Of course, the inner and outer walls of housing  62  would have to be extended upward and downward. Alternatively, separate housings for the bitter stacks could simply be attached to housing  62 . 
   Having now seen the fundamental concepts of the split Florida-helix design, the reader may wish to know how the design could be incorporated into a large magnet. At least as of the present time, the manufacturing of the Florida-helix is more difficult than creating a Florida-Bitter stack. Thus, it may be advantageous to combine the split Florida-helix with one or more Florida-Bitter coils. 
   The magnet shown sectioned in half in  FIG. 19  includes such a combination. The illustration includes the fundamental components needed to illustrate the novel concepts. However, the reader should note that many commonly understood features needed to physically implement the actual design have been omitted. An actual working magnet would need to include insulated conductor paths, various fluid seals, and probably an array of tie rods to clamp the entire assembly together. None of these commonly understood features are shown. With that proviso in mind, the assembly will be explained. 
   The magnet&#39;s housing comprises inner housing  90 , outer housing  88 , and four elliptical port bounding walls (as for housing  62 ). The ends are sealed by a pair of end caps  92 . Cooling inlet  94  feeds coolant into the housing and cooling outlet  96  removes it. Four nested coils are located concentrically within the jacket. In this version the two inner coils include a split Florida-helix assembly in the proximity of the elliptical ports. 
   The innermost coil has split Florida-helix assembly  74  surrounding the ports. A Florida-Bitter coil is clamped to the top and bottom of this split Florida-helix assembly (similar to the arrangement shown in  FIG. 18 ). This Florida-Bitter coil is denoted as first Bitter coil  80 . It is actually split into two portions, with half lying above the split Florida-helix assembly and half lying below. 
   The second coil also has a split Florida-helix assembly at its core. It is joined to second Bitter coil  82 . Third Bitter coil  84  and fourth Bitter coil  86  do not include a split Florida-helix assembly. Instead, they include a spacer  78 , which conforms to the shape of the elliptical ports (A spacer is used to simplify the design. The reader will recall from reviewing  FIG. 21  that little field strength is lost by not using an elliptical current path in the outer regions of the stack). In these two outer coils, current is carried around the ports by a bridging shunt. 
   As for prior art designs, the operation of a split Florida-helix at high current densities generates substantial mechanical forces and substantial heat. These considerations obviously affect the design of a working product.  FIG. 22  shows a refined embodiment of lower half split Florida helix  22 . The cooling slot locations have been refined so that the cooling slots are symmetric about the centerline of each of the interface surfaces  24 . This feature allows the coolant flow to divide evenly around elliptical port bounding walls  68  (which are shown in  FIG. 15 ). The embodiment of  FIG. 22  also includes a radial array of elongated tie rod holes  58 . These are only half-embedded—meaning that about ½ of each tie rod&#39;s cross section actually intrudes into the split Florida-helix. 
   As for all the prior examples, an insulator must be placed within the helical slot to ensure that the electrical current assumes a helical path. When the embodiment of  FIG. 22  is placed in a completed assembly, the array of tie rods are used to clamp the assembly tightly together. The tie rods help to resist the substantial mechanical forces generated by the magnet&#39;s operation. Lower-half-split Florida-helix  22  will be held in position largely by the engagement of the tie rods within elongated tie rod holes  58 . 
   Of course, the embodiment shown in  FIG. 22  is designed to mate with a corresponding upper half. Electrical current will pass between the two halves through the four interface surfaces  24 . It is therefore important to maintain alignment between these interface surfaces. It is also important to maximize the surface area available for contact. The reader will observe in  FIG. 22  that substantial surface area in the interface surfaces is lost to the cooling slots. It is therefore preferable to redirect the cooling slots around the interface surfaces. 
     FIG. 23  shows a detail view of another embodiment. In this version, the cooling slots have been modified to pass around the interface surfaces. Modified cooling slots  112  do not pass through the interface surface, but rather pass around it.  FIG. 24  shows the same interface surface from a different perspective. The dashed lines indicate the bounding walls of the cooling slots nearest the outer perimeter. The reader will observe that the cooling slot which would have previously passed through interface surface  24  has been modified to include angled slot wall  118 . The opposite end of this cooling slot is bounded by straight slot wall  116 . Thus, the cooling slot which would have passed through the interface surface actually tapers in order to pass around the interface surface. The same is true for the slot found on the right side of the interface surface in the view. The same is also true for the cooling slots in the upper half of the split Florida-helix. The reader will observe that for the particular embodiment shown, eight cooling slots had to be modified for each interface surface (four per side). Of course, an actual design might include many more concentric rings of cooling slots than have been illustrated in the drawing views. Any slot that would pass into the interface surface would need to be modified. 
     FIG. 23  shows another modification which helps to maintain alignment between mating interface surfaces. Each interface surface includes three holes which run parallel to the magnet&#39; central bore. These are designated as stabilizing pin receivers  114 . Three rigid pins are placed within these holes, with approximately half of the pin designed to lie within the lower half of the split-Florida helix and half of the pin designed to lie within the upper half of the split-Florida helix. Thus, the pins placed in these stabilizing pin receivers help to ensure the alignment of the corresponding interface surfaces. 
     FIG. 25  is the same schematic depiction of a magnet incorporating split Florida-helices that was originally shown n  FIG. 19 . However,  FIG. 25  includes arrows depicting the general flow of coolant through the magnet. Coolant flows vertically downward through each coil until it reaches the mid-plane, where it encounters the radial access ports. The coolant must then flow around the access ports before continuing downward.  FIG. 26  shows split Florida-helix assembly  74  (which could comprise the mid-plane of the innermost coil in the magnet of  FIG. 25 ). A cut has been made through the stack in order to reveal internal features. Elliptical port bounding wall  68  creates a fluid boundary which the coolant must pass around. Returning briefly to  FIG. 22 , the reader will note that each port through the split Florida-helix is defined by a port relief surface  128 . Returning now to  FIG. 26 , the reader will observe that a gap exists between the exterior of elliptical port bounding wall  68  and port relief surface  128 . The coolant must flow through this gap in order to pass around the port. 
     FIG. 27  shows a detailed elevation view of the cut illustrated in  FIG. 26 . The reader will observe how the cooling slots  60  are symmetrically arrayed about the centerlines of the access ports. The arrow depicts the flow of coolant around elliptical port bounding wall  68 . Coolant flow gap  122  is created by port relief surface  128  and elliptical port bounding wall  68 . The reader will observe that the gap is not constant. Near port mid point  124  the gap is relatively narrow. It then widens proceeding toward port boundary  126 . The gap is preferably optimized to carry the expected flow volume. Above the port, more flow volume is encountered when proceeding from port mid point  124  toward either port boundary  126 . Thus, the gap widens. Below the port, less flow volume is seen when proceeding back toward the port mid point. Thus, the gap narrows again. 
     FIG. 27  also shows the mating of corresponding interface surfaces  24 . The dashed lines indicate angled slot walls  118  in the cooling slots that have been modified to pass around the interface surfaces. 
   The reader will therefore understand how the split Florida-helix can operate as a stand-alone coil, or as a part of a more complex magnet. It can also be used as a component in a resistive or hybrid magnet. Many other applications are possible. Accordingly, the scope of the invention should be set by the claims rather than by the specific examples given.