Abstract:
A superconducting magnetizer assembly includes a coil pack including an inner coil configured to generate a first magnetic field in response to an electric current supplied to the inner coil, an outer coil being disposed about the inner coil and configured to generate a second magnetic field in response to an electric current supplied to the outer coil, a non-conductive end spacer disposed between an end winding of the inner coil and an end winding of the outer coil, and a container to house the inner and outer coils; and a yoke disposed proximate the coil pack being configured to constrain the first and second magnetic fields to reduce the strength of the first field at the end winding of the inner coil, wherein the yoke comprises an annular ring configured to at least partially envelop the coil pack.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to the magnetization of permanent magnets, and more specifically, to the magnetization of magnets disposed within cylindrical structures using one or more superconducting materials. 
         [0002]    Many electrical machines include one or more electric motors. Such electric motors typically include a rotor having permanent magnets disposed within the bulk of the rotor. During rotation, the rotor, having the permanent magnets, produces a rotating magnetic field that interacts with a stator. This electromagnetic interaction results in the conversion of electromagnetic energy into mechanical motion that drives the machine. 
         [0003]    Two approaches are typically used for the assembly of rotors having permanent magnets. In one approach, shaped materials are magnetized to generate the permanent magnets before they are disposed within the bulk of the rotor. This approach may present several drawbacks. For instance, fully magnetized permanent magnet pieces can be subject to electromagnetic interaction with any surrounding objects, such as other adjacent or proximate magnets, which in turn adds to the complexity of their handling procedures and insertion into the rotor. In a second approach, the shaped materials are first disposed within the rotor and a magnetizer is used to magnetize the permanent magnets. Such an approach is typically referred to as an in-situ magnetization process. 
         [0004]    The second approach can also present several drawbacks. To name a few, the energy and fabrication costs for conventional resistive magnetizers capable of generating a sufficient magnetic field flux for the magnetization process can be prohibitive. For example, some in-situ magnetizers are able to produce small magnetic fields sufficient only to magnetize small permanent magnets made of certain materials or grades (e.g., alnico and ferrite) that have low intrinsic coercivity (i.e., materials that can be easily demagnetized). However, many emerging applications for permanent magnet electric machines, such as wind turbine applications, or traction (e.g., magnetic bearing and braking) applications, would benefit from the use of high-coercivity rare-earth permanent magnet materials, which can often require strong magnetic fields. Moreover, as the permanent magnets increase in size, their magnetization becomes increasingly difficult due to inadequate field penetration produced by typical magnetizers. It should therefore be appreciated that due to physical constraints in addition to economic considerations, the in-situ magnetization of such materials is typically very difficult to deliver with conventional restive systems. Accordingly, it is now recognized that a need exists for a magnetizer capable of magnetizing rare-earth, high-coercivity materials in an efficient manner. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    The present embodiments are generally directed towards such magnetization. In one embodiment, a superconducting magnetizer assembly is provided. The assembly includes a coil pack having an inner coil including a first superconducting magnet material, the coil being configured to generate a first magnetic field in response to an electric current supplied to the coil, and an outer coil including a second superconducting magnet material, the outer coil being disposed about the inner coil and being configured to generate a second magnetic field in response to an electric current supplied to the outer coil. The coil pack also includes a container configured to house the inner and the outer coils. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0007]      FIG. 1  is an embodiment of an assembly having a superconducting magnetizer assembly and a rotor disposed within the magnetizer assembly, the magnetizer assembly including a plurality of superconducting coils configured to magnetize permanent magnet blocks within the rotor; 
           [0008]      FIG. 2  is an embodiment of a coil configuration for the superconducting coils of  FIG. 1 , the coil configuration including a non-conductive end spacer configured to reduce the peak field at the coil; 
           [0009]      FIG. 3  is a perspective illustration of an embodiment of a curved cryostat configured to house superconducting coils, and the curved cryostat allows the coils to interface with an annular rotor so as to facilitate magnetization of permanent magnets within the rotor; 
           [0010]      FIG. 4  is a schematic illustration of the cryostat of  FIG. 3 ; 
           [0011]      FIG. 5  is an end-on illustration of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly utilizing the curved cryostat of  FIGS. 3 and 4 ; 
           [0012]      FIG. 6  is a perspective illustration of an embodiment of a dished cryostat configured to house superconducting coils, and the dished cryostat allows the coils to interface with an annular rotor so as to facilitate magnetization of permanent magnets within the rotor; 
           [0013]      FIG. 7  is a schematic illustration of the cryostat of  FIG. 6 ; 
           [0014]      FIG. 8  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly utilizing the dished cryostat of  FIGS. 6 and 7 ; 
           [0015]      FIG. 9  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly utilizing an external yoke configured to enhance the field alignment within the permanent magnet material, and the superconducting magnetizer assembly is arranged to allow the magnetization of 3 poles in one operation; 
           [0016]      FIG. 10  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly utilizing a thin-profile external yoke, widened coil packs, and yoke blocks interfacing with the coil packs; 
           [0017]      FIG. 11  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly not having an external yoke but having widened coil packs, and yoke blocks interfacing with the coil packs; 
           [0018]      FIG. 12  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly not having an external yoke but having widened coil packs and an internal yoke for interfacing with the coil packs; 
           [0019]      FIG. 13  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly having a number of superconducting magnets sufficient to magnetize all of the poles of a rotor in one operation; 
           [0020]      FIG. 14  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly having a number of superconducting magnets interfacing with internal yokes, the superconducting magnets being sufficient to magnetize all of the poles of a rotor in one operation, but without the use of an external return yoke; 
           [0021]      FIG. 15  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly having a number of superconducting magnets interfacing with internal yokes and being enclosed by an external yoke, the superconducting magnets being sufficient to magnetize all of the poles of a rotor in one operation; 
           [0022]      FIG. 16  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly having a combination of at least two different superconducting materials in the form of interleaving coil packs capable of magnetizing 3 poles in a single operation; 
           [0023]      FIG. 17  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly having a combination of at least two different superconducting materials, one of the superconducting materials being configured to act as a main magnetization circuit to magnetize each pole in the rotor individually; 
           [0024]      FIG. 18  is an end-on illustration of an embodiment of an assembly including a superconducting magnetizer assembly and a rotor disposed within the assembly, the superconducting magnetizer assembly having hybrid coil packs forming a main magnetization circuit and including one of the superconducting materials being disposed on an inner, high field portion of the coil pack and the other superconducting material being disposed on an outer, low field portion of the coil pack. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    The present disclosure is generally directed towards improved systems and methods for the magnetization of materials disposed within a bulk material, such as the magnetization of as-formed permanent magnets disposed within an electric motor rotor. In accordance with the disclosed embodiments, one or more superconducting materials may be utilized to perform the in-situ magnetization of the as-formed permanent magnets. Moreover, the superconducting materials may be disposed in specially configured packs so as to facilitate the magnetization of the as-formed permanent magnets in a non-cubic shaped matrix, such as within the cylindrical rotor described above. Moreover, embodiments of magnetizer assemblies having features for controlling the magnetic fields generated by the superconducting materials are disclosed. Accordingly, to facilitate discussion of the present approaches towards such improved embodiments,  FIG. 1  illustrates an assembly  10  including a rotor  12  having as-formed permanent magnets  14  (e.g., rare-earth magnets such as neodymium magnets) disposed within a bulk  16  (e.g., laminations) of the rotor  12 . In one embodiment, the permanent magnets  14  may be NdFeB magnets. The rotor  12  is disposed inside of a superconducting magnetizer assembly  18  having an annular opening  20  configured to receive the rotor  12 . In some embodiments, the superconducting magnetizer assembly  18  may support at least a portion of the weight of the rotor  12  as the magnetization process is performed. 
         [0026]    In a general sense, the superconducting magnetizer assembly  18  includes a set of superconducting coils  22  wound in a racetrack-like manner. Such a configuration, as referred to herein, may be racetrack coils  22 . The racetrack coils  22 , as noted above, may incorporate a number of superconducting materials, for example niobium-3 tin (Nb 3 Sn), niobium-titanium (NbTi), MgB 2  magnesium diboride, vanadium gallium (V 3 Ga), YBCo, or combinations thereof in one or more coils such as an inner coil and an outer coil, as will be discussed in further detail below. In the illustrated embodiment, and in the embodiments described below with respect to  FIGS. 2-15 , the coils  22  are NbTi coils. However, it should be noted that the superconductor material or materials chosen may be application specific and may contain a High Temperature Superconducting or Low Temperature Superconducting material, or both. Generally, the racetrack coils  22  produce a magnetic field when a current is passed through the coils. In some embodiments, the materials mentioned above that form the racetrack coils  22  exhibit decreased resistance when cooled. Accordingly, in such embodiments the racetrack coils  22  may be cooled so as to produce maximum magnetic flux. 
         [0027]    Using cooling agents such as liquid helium, it may be possible to approach absolute zero in temperature (i.e., 0 Kelvin (K)), for example, below about 40 K. In one embodiment, liquid helium, which has a temperature of approximately 4 K, may be used as the active coolant to maintain the temperature of the racetrack coils  22  at the temperature of the liquid helium. It will therefore be appreciated that each of the racetrack coils  22  may be disposed in a cryostat  24 , which may include other features such as thermal transfer agents (e.g., thermally conductive rods, heat pipes, thermal buses). Together, the racetrack coils  22  and the cryostats  24  each form coil packs  26 . 
         [0028]    Because the racetrack coils  22  are formed from superconducting materials, such as NbTi and/or Nb 3 Sn, which are capable of handling very high current densities, thermal dissipation may be reduced compared to conventional resistive magnetizers. That is, in conventional resistive magnetizers, the system must be pulsed to attain the required field levels for short periods of time. For instance, magnetizers incorporating superconducting coils may be energized and de-energized at much slower speeds, such as at ramp rates of ˜1 Tesla per minute, compared to conventional magnetizers incorporating conventional resistive coils, which need to be energized and de-energized at ramp rates of ˜1 Tesla per second. It should be noted that such ramp rates may be achieved with power supplies much smaller than those required for conventional magnetizers. 
         [0029]    In the illustrated embodiment of  FIG. 1 , the superconducting magnetizer assembly also includes a yoke  28 , which may be made from iron, permendur, or similar materials, or any combination thereof. The yoke  28  is generally configured to improve efficiency of the magnetization process by reducing fringe magnetic fields and balancing radial forces produced by the coils  22 . In the illustrated embodiment, the yoke  28  includes a plurality of openings  30  configured to house each of the coil packs  26 . In this embodiment the rotor  12  includes six pairs of permanent magnets  14  or “poles,” and the superconducting magnetizer assembly includes three coil packs  26  each configured to magnetize a pair of permanent magnets  14 . Therefore, in the depicted embodiment, at least two operations must be performed so as to magnetize the rotor  12 . For example, an embodiment of such a process may include energizing the racetrack coils  22  so as to magnetize the permanent magnets  14  adjacent to their respective coil packs  26 , followed by a clockwise or counter-clockwise rotation of the rotor  12  so as to bring non-magnetized permanent magnet pairs in proximity to the coil packs  26 , which allows magnetization of the remaining permanent magnets  14 . 
         [0030]    While the racetrack coils  22  in accordance with  FIG. 1  may be generally applicable to the magnetization of rotors, it should be noted that as the size of the rotor  12  increases, the required volume of the magnetic field produced by each of the racetrack coils  22  must also increase so as to provide sufficient magnetization of the permanent magnets  14 . However, as noted above, it can be very difficult for conventional resistive magnetizers to produce such fields. 
         [0031]    For example, in embodiments where the diameter of the rotor  12  is on the order of 0.1 m and above, the racetrack coils  22 , in a simple wound configuration, may not be sufficient to provide sufficient magnetic field saturation of the permanent magnets  14 . Accordingly, it may be desirable to manipulate the magnetic field produced by the coils  22  to as to provide more efficient magnetization. In accordance with the present disclosure, one approach, which is illustrated in  FIG. 2 , is to increase saturation by the racetrack coils  22  to reduce and move the peak magnetic field produced by the racetrack coils  22  from an end winding section  32  of the coils  22  to a long section  34  of the coils  22 , the sections being more clearly illustrated in the inset of  FIG. 1 . Other approaches may include shaping the cryostat  24  so as to bring the racetrack coils  22  in closer proximity with the rotor  12 , modifying the placement of or removing the yoke  28  to improve the magnetic field circuit, using multiple superconducting materials for the coils  22 , or any combination thereof. Such embodiments are described in further detail with respect to  FIGS. 3-18  below. 
         [0032]    Therefore, keeping in mind the general characteristics of the assembly  10  of  FIG. 1 , an embodiment of the approach of moving the peak field produced by the coils  22  is illustrated in  FIG. 2 . Specifically,  FIG. 2  is a diagrammatic illustration of one of the racetrack coils  22  having a non-conductive end spacer  40  disposed between an outer coil  42  and an inner coil  44  of the windings of the coils  22 . Generally, the outer coil  42  is disposed about the inner coil  44 , and the superconducting magnet materials that form each of the coils may be the same, or may be different, as will be discussed in detail below. In the illustrated embodiment, the outer coil  42  and the inner coil  44  include the same superconducting magnet material. When a current is passed through the inner coil  44  and/or the outer coil  42 , respective first and second magnetic fields may be produced. In some embodiments, one of the coils may have a higher critical current than the other. In such embodiments, the coil having the higher critical current may produce a stronger magnetic field. Such embodiments are discussed below. It should be noted that the peak magnetic field produced by such a racetrack coil  22  may be approximately 90%, 88%, or 85% lower than the peak magnetic field of the racetrack coils of  FIG. 1  with no end spacer. For example, in an embodiment, the peak field may be reduced from approximately 8.8 Tesla (T) to approximately 7.7 T. Moreover, because the peak field is now moved to the long portion  34  of the coils  22 , magnetic flux is produced by a greater area of the coils  22 , which may provide a greater area of saturation to magnetize the permanent magnets  14 . 
         [0033]    Another approach to increasing magnetic efficiency, as noted above, is to shape the cryostat  24  so as to allow the coils  22  to be in closer proximity to the rotor  12 . Embodiments of such approaches are illustrated with respect to  FIGS. 3-8 , and may be used in lieu of, or in combination with, the embodiment illustrated in  FIG. 2 . Specifically,  FIG. 3  depicts a cryostat  50  having a flat surface  52  that is configured to be placed against the yoke  28  or other supporting structure. The cryostat  50  also includes a curved surface  54 , which may be configured to allow the coils  22  inside the cryostat  50  to be disposed radially around the circumference of the rotor  12 . 
         [0034]      FIG. 4  depicts the arrangement of the coils  22 , which may have constant perimeter end windings, or other winding configurations which fit closely on a cylindrical surface, so as to allow more penetration of the magnetic field into the permanent magnets  14 . An assembly  60  having the superconducting magnetizer assembly  18 , the rotor  12 , and the curved cryostat  50  is depicted in  FIG. 5 . As may be appreciated, the cryostat  50  is placed against the circumferential bounds of the rotor  12  so as to allow the coils  22  to be disposed in a close-spaced relationship. It should be noted that in the embodiment depicted in  FIGS. 3-5 , the cryostat  50  allows the yoke  28  to be constructed from a single piece having the annular opening  20  configured to receive the rotor  12 . 
         [0035]    An embodiment of a similar approach is depicted in  FIG. 6 , which illustrates a dished cryostat  70  having flat surfaces  72  bounding either side of a recess  74  within the cryostat  70 . The recess  74  may be considered a dish that is formed so as to receive a portion of the rotor  12  therein. The placement of the coils  22  in the dished cryostat  70  is illustrated in  FIG. 7 , which shows the long section of the coil  22  as being at least as long as the length of the recess  74 . Moreover, the width of the end section  32  of the coil  22  is at least as large as the width of the recess  74 . Such spatial relationships may allow effective magnetic field penetration into the permanent magnets  14  by the coils  22  in combination with the approach described with respect to  FIG. 2 . 
         [0036]      FIG. 8  depicts an embodiment of an assembly  80  using the dished cryostat  70 . As illustrated, when placed over the rotor  12 , each of the cryostats  70  has the flat surfaces  72  extending over the rotor  12 , which is disposed within the respective recesses  74  of each of the cryostats  70 . In the illustrated embodiment, the assembly  80  includes a yoke  82  formed from a plurality of sections  84 . Each section  84  is configured to receive one cryostat  70  each, although in other embodiments each section  84  may include more than one cryostat  70 . The yoke  82  of the assembly  80  may require such sections  84  due to the manner in which each of the cryostats  70  interface with the rotor  12 . For example, each of the sections  84  may be removed and replaced in the directions depicted by arrows  86 . 
         [0037]    As noted above, another approach to improving the efficiency of the magnetization of the permanent magnets  14  is to vary the magnetic circuit by changing geometries, arrangements, and/or magnetic materials. Such embodiments are illustrated with respect to  FIGS. 9-12 .  FIGS. 9 and 10  depict embodiments where the yoke is retained, and  FIGS. 11 and 12  depict embodiments where the yoke is not present. Again, in some embodiments, certain magnetic materials may be replaced with others. 
         [0038]    One such embodiment of an assembly  90  is depicted in  FIG. 9 , which has the same geometric configuration as the assembly  10  of  FIG. 1 . In the embodiment of  FIG. 9 , the assembly  10  has a yoke  92  that is constructed from permendur, which is an alloy of cobalt and iron. By replacing the iron yoke with the permedur yoke  92 , the magnetizing field normal to the surface of the coil packs  26 , the peak magnetic fields produced by the racetrack coils  22 , and the operating margin is varied. As an example, the minimum magnetizing fields produced by the racetrack coils  22  may be increased, but the maximum magnetizing fields may be decreased. Peak magnetic field on the superconducting element may also be decreased, along with improving the operating margin of the superconductor. 
         [0039]    In the embodiment illustrated in  FIG. 10 , an assembly  110  includes a permendur yoke  112  having a thinner profile than the yokes of the embodiments described above. Additionally, the yoke  112  includes a series of block protrusions  114  that are disposed proximate the center of each of a set of widened coil packs  116116 . In the assembly  110 , the magnetizing field normal to the surface of the coil packs  116  and the peak magnetic fields produced by the racetrack coils  22  decrease compared to assembly  100 , but the operating margin increases, for example by over 25% (e.g., from an operating margin of about 15% to an operating margin of about 19%), compared to assembly  100 . 
         [0040]    As noted above,  FIGS. 11 and 12  illustrate embodiments wherein the yoke is not included in the assembly. It should be noted that when no external yoke is used, other features, such as a support stand or similar structure may be included so as to balance the radial forces produced by the superconducting magnets. Specifically,  FIG. 11  illustrates an assembly  120  having a similar configuration to that of the assembly  110  illustrated in  FIG. 10 , but not having the thin profile yoke  112 . However, it will be appreciated that the permendur blocks  114  are maintained within the assembly  120 , for example using other support structures. In the assembly  120 , the magnetizing field normal to the surface of the coil packs  116  and the peak magnetic fields produced by the racetrack coils  22  decrease compared to assembly  110 , and the operating margin increases, for example by about 5% (e.g., from an operating margin of about 19% to an operating margin of about 20%), compared to assembly  110 . 
         [0041]      FIG. 12  depicts an embodiment of an assembly  130  wherein the permendur blocks  114  of assembly  120  are removed, and a set of permendur blocks  132  are placed towards the end windings of the coil packs  116 . Placing the permendur blocks  132  in such a location may reduce the peak magnetic field at the racetrack coils  22 . Indeed, in the assembly  130 , the magnetizing field normal to the surface of the coil packs  116  and the peak magnetic fields produced by the racetrack coils  22  decrease compared to assembly  120 , with the operating margin remaining about the same as the assembly  120 . 
         [0042]    While varying the geometry and/or magnetic materials present within the superconducting magnetizer assembly may have certain advantages, it may be desirable to increase the number of magnetizing poles within the magnetic circuit. For example, by increasing the number of magnetizing poles (i.e., increasing the number of coil packs), it may be possible to decrease the total number of operations required to magnetize a rotor. Further, in having a larger number of magnetizing features, the magnetization efficiency may increase. Such embodiments are illustrated diagrammatically in  FIGS. 13-15 . 
         [0043]    Specifically,  FIG. 13  illustrates an assembly  140  having six coil packs  26 , each having racetrack coils  22  (with end spacers  40 ) so as to generate six sets of magnetic fields, one for each of the six pairs of permanent magnets  14 . It will be appreciated that when magnetization is performed using the assembly  140  illustrated in  FIG. 13 , that only one operation may be required to fully magnetize the rotor  12 . Additionally, as illustrated, the assembly  140  includes the iron yoke  28  to improve magnetization efficiency, reduce stray magnetic fields, and balance radial forces. In the assembly  140 , the magnetizing field normal to the surface of the coil packs  26  and the peak magnetic fields produced by the racetrack coils  22  may be much higher compared to the assemblies described with respect to FIGS.  1  and  9 - 12 . However, operating margin decreases greatly, for example by over 400% (e.g., from an operating margin of about 13% to an operating margin of about 3%), compared to assembly  10 . 
         [0044]      FIG. 14  illustrates an assembly  150  having a series of six coil packs  152  including the coils  22  and end spacers  40  for magnetizing each pole in one operation. The assembly  150  does not have an external yoke, but includes internal iron yokes  154  that are internal to the coil packs  152  so as to improve magnetization efficiency and reduce the peak fields at each coil  22 . For the assembly  150 , both the magnetizing field and the peak field decrease as compared to assembly  140 , with operating margin increasing when compared to the same. 
         [0045]      FIG. 15  illustrates an embodiment of an assembly  160  having features similar to those of assemblies  140  and  150  of  FIGS. 13 and 14 , respectively. Specifically, assembly  160  includes the coil packs  152  having the internal iron yoke  154  so as to control peak field and improve magnetization efficiency. Additionally, the assembly  160  includes the external iron yoke  28 , which may balance radial forces as well as further reduce peak fields and improve magnetization efficiency. Indeed, when compared to assembly  150 , assembly  160  has increased magnetization efficiency, reduced peak field, and increased operating margin. 
         [0046]    It should be noted that the utilization of a high field wind and react (or react and wind) superconductor, for example Nb 3 Sn, in all of the coil packs may be prohibitive from a logistical and cost standpoint. For example, Nb 3 Sn coils require features to offset the forces resulting from the large electromagnetic interactions. Accordingly, it may be desirable to incorporate features into the embodiments described above so as to mitigate such concerns. One such approach is to incorporate other superconducting materials, such as niobium-titanium (NbTi), vanadium gallium (V 3 Ga), and so forth, into the assemblies described herein. Accordingly,  FIGS. 16-18  illustrate embodiments wherein at least two different types of superconducting materials are incorporated into the magnetizing assembly. 
         [0047]      FIG. 16  illustrates an embodiment of an assembly  170  having Nb 3 Sn coil packs  172  having Nb 3 Sn racetrack coils  174  and end spacers  40  interleaved with NbTi coil packs  176  having NbTi racetrack coils  178 . It should be noted that in order to facilitate discussion, each coil pack is illustrated as a cross-section. While the NbTi coils  178  do not perform any substantial magnetization of the permanent magnets  14  as the Nb 3 Sn coils  174  do, this efficiently minimizes the use of high field wind and react superconductors in the overall assembly, so that magnetic efficiencies and peak field reductions may be achieved similar to those exhibited by the embodiments illustrated in  FIGS. 13-15 . However, rather than being able to magnetize all of the magnetic poles in one operation as with assemblies  140 ,  150 , and  160 , two operations must be performed for the assembly  170 , wherein three of the pairs of permanent magnets  14  are magnetized, followed by rotation and magnetization (i.e., re-energizing the coils). 
         [0048]    In another embodiment, which is illustrated as assembly  180  of  FIG. 17 , rather than interleaving the coils, two of the sets of Nb 3 Sn coils  174  may be disposed proximate one another, with the other four sets of coils being the NbTi coils  178 . The assembly  180  therefore has one main magnetizing circuit, which is formed by combining the two sets of Nb 3 Sn coils  174  in a single cryostat  182 . Because the Nb 3 Sn coils  174  are disposed proximate one another, the main magnetizing circuit magnetizes two pairs of the permanent magnets  14  at once. Accordingly, three operations are required to magnetize all of the permanent magnets  14  in the embodiment depicted in  FIG. 17 . In a similar manner to the Nb 3 Sn coils  174 , the NbTi coils  178  may be combined into a single cryostat  184 . Such an arrangement is generally configured to increase the inter coil pack distance to help offset inter coil pack forces. 
         [0049]    To further reduce the amount of Nb 3 Sn that is utilized, it may be possible to hybridize the coils, wherein a single coil pack includes both NbTi coils and Nb 3 Sn coils. Such an embodiment is illustrated with respect to  FIG. 18 . Specifically,  FIG. 18  illustrates an assembly  190  having a main magnetization cryostat  192 , and four separate NbTi coil packs  176  each having NbTi coils  178 . The main magnetization cryostat  192  houses two hybrid coil sets  194  having both Nb 3 Sn coils and NbTi coils. Specifically, as shown in the expansion, the Nb 3 Sn coils are employed in the inner, high field section  198  and the NbTi are employed in the outer, lower field section  200 . Such an arrangement allows the Nb 3 Sn coils to have maximum proximity to the permanent magnets that are being magnetized, which allows for complete local magnetic saturation of two pairs of the permanent magnets  14 . In the illustrated embodiment, the Nb 3 Sn coils are stepped in to allow more volume for force containment resulting from coil interactions. Optionally, the non-conductive end spacer  40  may be used to further reduce peak fields. 
         [0050]    Technical effects of the invention include lower running costs of the superconducting system, a smaller footprint than conventional magnetizers, and the ability to be deployed without the requirement of special facilities for operation (due to the lower power requirements). Moreover, the present embodiments lead to higher magnetization throughput than a conventional system. The embodiments describe herein may be modular, such as by using the separate coil packs described above, which allows components to be replaced as needed. Additionally, a greater percentage of magnetization of permanent magnets may allow more robust and longer lifetime magnetically-driven equipment, such as turbines, brakes, bearings, and so forth. 
         [0051]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. It should also be understood that the various examples disclosed herein may have features that can be combined with those of other examples or embodiments disclosed herein. That is, the present examples are presented in such as way as to simplify explanation but may also be combined one with another. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.