An electromagnet having at least one access port oriented perpendicularly to the electromagnet'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's central bore to the magnet'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.

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'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 theIEEE 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. 1shows an electromagnet created by wrapping conductor100around central bore104in a helical path. The two ends of the helical path may be provided with a flat30to facilitate mounting the coil. Helical gap28is typically filled with an insulator of some sort to ensure that the current flows through the helical path.

The version shown inFIG. 1does 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 inFIG. 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. 2shows a prior art Bitter-disk magnet. End plate40is the anchoring point for a number of circumferentially-spaced tie rods44. In practice tie rods44have 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 plate40, tie rods44are added. A series of conducting disks36are then slipped onto tie rods44. The reader will observe that each conducting disk36has a series of holes designed to accommodate tie rods44. Conducting disks36are made of thin conductive material, such as copper or aluminum.

Turning briefly toFIG. 4, the reader may observe conducting disk36in more detail. Tie rod holes46are uniformly spaced around its perimeter. Cooling holes54are also uniformly spaced about conducting disk36. Cut52is 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 disk36forms one turn of a helix having a shallow pitch. Upper side50of cut52is higher than lower side48. 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 toFIG. 2, the reader will observe that six conducting disks36are initially placed over tie rods44(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 are15tie rods44). Turning toFIG. 5, the effect of the rotational indexing may be more readily observed.

Six conducting disks36have been assembled to create one conductor turn42. Conducting disks36have 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 side50of one conductor disk36lies over upper side50of the conductor disk36just below it. The disks inFIG. 2are 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 disks36form one integral conductor having a helical path—albeit with a very shallow pitch.

Still looking atFIG. 2, the description of the prior art device will be continued. The reader will observe that four conductor turns42are shown in the assembly (in the uncompressed state). In reality, many such conductor turns42will be stacked onto tie rods44. 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 plate40(which makes contact with the underside of the lowermost conducting disk36). A second end plate40(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 plate40(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 turns42on the device, the electrical current will not flow in the desired helix. Rather, it will simply flow directly from the lower end plate40to the upper end plate40in a linear fashion. An additional element is required to prevent this.

Insulating disks34are placed within each conductor turn42to prevent the aforementioned linear current flow. Each insulating disk34is made of a material having a very high electrical resistance. The dimensional features of each insulating disk34(tie rod holes, cooling holes, etc.) are similar to the dimensional features of conducting disks36. Each conductor turn42incorporates at least one insulating disk34nested into the stack.FIG. 3shows a detail of this arrangement. The reader will observe the upper portion and lower portion of each insulating disk34(both ends of each disk are labeled as “34” in the view so that the reader may easily distinguish them from conducting disks36). The reader will also observe how each insulating disk34nests into the helix formed by the six conducting disks36.

FIG. 5also illustrates this arrangement. Insulating disk20is placed immediately over the first conducting disk36. It then follows the same helical pattern as the conducting disk36. Returning now toFIG. 2, the cumulative effect of this construction will be explained. The four conductor turns42shown inFIG. 2are identical. When they are compressed together, the four insulating disks34will force the current to flow through one continuous helix through the stacked conducting disks36. 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 magnet32, 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 plates40in place, the end plates are mechanically forced toward each other. The lower ends of tie rods44are attached to the lower end plate40. The upper ends typically pass through holes in the upper end plate40. The exposed upper ends are threaded so that a set of nuts can be threaded onto the exposed ends of tie rods44and 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 magnet32generates 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 plate40, and bounded on its upper end by the upper end plate42. An outer cylindrical wall is provided outside the outer perimeter of the disks, extending from the lower end plate42to the upper end plate42. 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). InFIG. 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 magnet32will 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 inFIG. 4uses 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. 6shows 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 disk56has elongated tie rod holes58to 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 disk56has cooling slots60in place of the conventional cooling holes. A series of such cooling slots are placed in concentric rings across the width of the disk.

FIG. 7shows a detailed view of a portion of Florida-Bitter disk56, 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'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's perimeter (rather than longitudinal cooling in a direction parallel to the magnet's central axis). Some type of spacer plate is typically added in the magnet's mid-plane.FIG. 20shows two spacer plates106. Each has a pair of radial access grooves108. Each also has an array of radial cooling channels110. 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's core in the transverse direction.

FIG. 20shows 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'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 inFIG. 20does 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 bore104. Thus, the design shown inFIG. 20sacrifices 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. 21is 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' mid plane. If spacers such as shown inFIG. 20are used, they will be placed on the X axis in the view.

The figure depicts the winding of a30Tesla magnet, using three concentric Bitter coils (first Bitter coil80, second Bitter coil82, and third Bitter coil84). 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 coil80actually lying next to the magnet'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'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 nFIG. 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's central bore to the magnet'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'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.

REFERENCE NUMERALS IN THE DRAWINGS

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a resistive magnet having access ports proximate its mid-plane. The reader will recall thatFIG. 1shows 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. 8shows a Florida-helix incorporating this modification (denoted as split Florida-helix10). It incorporates a helically wrapped conductor100around a central bore104. Flats30are preferably provided on either end. Cooling slots60are also provided, in a configuration similar to that shown for the Florida-Bitter disk inFIGS. 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 inFIG. 8can be created by cutting a helically-wound gap28through a cylindrical “blank.” The gap is typically cut using a wire EDM process. Four ports12—radially arrayed at 90 degree increments—are cut from the coil's exterior into central bore104. The ports diverge as one proceeds away from the coil's central axis. In other words, they grow wider proceeding towards the coil's exterior. This allows a more free path for emissions coming from a sample located in the coil'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. 9better illustrates this feature. InFIG. 9, the split Florida-helix has been sectioned in half through two of the ports12. In the upper and lower portions of the coil the pitch of the helical gap28is constant and relatively shallow (shallow pitch regions14). However, in the middle portion, the pitch of the helical gap is significantly increased (steep pitch region16).

FIG. 10shows an elevation view of the coil, rotated to better display the pitch of the helical gap through steep pitch region16. 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) region14and the steep pitch (low current density) region16can 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 ofFIG. 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 gap28. 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's core, proximate the ports. A beam will then be directed in one end of the magnet, through central bore104. The beam will strike the sample, and emissions will then radiate in all directions. Ports12can 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. 11shows a split Florida-helix incorporating a refined version of the access ports. Elliptical ports18diverge 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. 12shows a section view through the embodiment having elliptical ports18. The other features are the same as the embodiment shown inFIGS. 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 inFIGS. 8 through 12illustrate the main features of the split Florida-helix in an uncluttered fashion. However, actual magnet designs would typically incorporate many more turns.FIG. 13shows a more realistic design. Shallow pitch region14includes a more shallow pitch for helical gap28and—consequently—many more conductor turns. Approximately the same steep pitch is used for steep pitch region16.

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'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 ports18. These walls must be joined to an internal wall passing through the coil's central bore. Likewise, they must be joined to an external cylindrical wall surrounding the coil's exterior. Practical manufacturing problems are immediately apparent, since joining such walls around the split Florida-helix will be very difficult.

FIG. 14presents 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-helix20and lower half split Florida-helix22. Each half has four interface surfaces24. 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 ofFIG. 13in 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. 15shows housing62, which is configured to house the split Florida-helix. Inner wall66and outer wall64are joined by four elliptical port bounding walls68. Each bounding wall terminates at an inner port boundary70on its inner extreme and an outer port boundary72on 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). Housing62can be made by many conventional methods, including casting the unit as an integral piece and fabrication as a weldment of smaller pieces.

FIG. 16illustrates the effective combination of housing62and the two halves of the split Florida-helix. Upper half split Florida-helix20is lowered into the housing from the top, while lower half split Florida-helix22is lifted into the housing from the bottom (or the housing may be lowered onto the lower half).FIG. 17shows the completed split Florida-helix assembly74.

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'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-helix74to continue the helical current path over a longer distance.FIG. 18shows this embodiment, with two Florida-Bitter disk stacks76in position and ready to be clamped to the assembly. Many such stacks could be added. Of course, the inner and outer walls of housing62would have to be extended upward and downward. Alternatively, separate housings for the bitter stacks could simply be attached to housing62.

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 inFIG. 19includes 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's housing comprises inner housing90, outer housing88, and four elliptical port bounding walls (as for housing62). The ends are sealed by a pair of end caps92. Cooling inlet94feeds coolant into the housing and cooling outlet96removes 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 assembly74surrounding the ports. A Florida-Bitter coil is clamped to the top and bottom of this split Florida-helix assembly (similar to the arrangement shown inFIG. 18). This Florida-Bitter coil is denoted as first Bitter coil80. 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 coil82. Third Bitter coil84and fourth Bitter coil86do not include a split Florida-helix assembly. Instead, they include a spacer78, which conforms to the shape of the elliptical ports (A spacer is used to simplify the design. The reader will recall from reviewingFIG. 21that 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. 22shows a refined embodiment of lower half split Florida helix22. The cooling slot locations have been refined so that the cooling slots are symmetric about the centerline of each of the interface surfaces24. This feature allows the coolant flow to divide evenly around elliptical port bounding walls68(which are shown inFIG. 15). The embodiment ofFIG. 22also includes a radial array of elongated tie rod holes58. These are only half-embedded—meaning that about ½ of each tie rod'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 ofFIG. 22is 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's operation. Lower-half-split Florida-helix22will be held in position largely by the engagement of the tie rods within elongated tie rod holes58.

Of course, the embodiment shown inFIG. 22is designed to mate with a corresponding upper half. Electrical current will pass between the two halves through the four interface surfaces24. 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 inFIG. 22that 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. 23shows a detail view of another embodiment. In this version, the cooling slots have been modified to pass around the interface surfaces. Modified cooling slots112do not pass through the interface surface, but rather pass around it.FIG. 24shows 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 surface24has been modified to include angled slot wall118. The opposite end of this cooling slot is bounded by straight slot wall116. 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. 23shows another modification which helps to maintain alignment between mating interface surfaces. Each interface surface includes three holes which run parallel to the magnet' central bore. These are designated as stabilizing pin receivers114. 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. 25is the same schematic depiction of a magnet incorporating split Florida-helices that was originally shown nFIG. 19. However,FIG. 25includes 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. 26shows split Florida-helix assembly74(which could comprise the mid-plane of the innermost coil in the magnet ofFIG. 25). A cut has been made through the stack in order to reveal internal features. Elliptical port bounding wall68creates a fluid boundary which the coolant must pass around. Returning briefly toFIG. 22, the reader will note that each port through the split Florida-helix is defined by a port relief surface128. Returning now toFIG. 26, the reader will observe that a gap exists between the exterior of elliptical port bounding wall68and port relief surface128. The coolant must flow through this gap in order to pass around the port.

FIG. 27shows a detailed elevation view of the cut illustrated inFIG. 26. The reader will observe how the cooling slots60are symmetrically arrayed about the centerlines of the access ports. The arrow depicts the flow of coolant around elliptical port bounding wall68. Coolant flow gap122is created by port relief surface128and elliptical port bounding wall68. The reader will observe that the gap is not constant. Near port mid point124the gap is relatively narrow. It then widens proceeding toward port boundary126. The gap is preferably optimized to carry the expected flow volume. Above the port, more flow volume is encountered when proceeding from port mid point124toward either port boundary126. 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. 27also shows the mating of corresponding interface surfaces24. The dashed lines indicate angled slot walls118in 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.