Force treatment of tokamak trioidal field coils.

Abstract

Some aspects relate to a toroidal field (TF) coil for a tokamak. The TF coil includes a first inner leg having teeth on a side of the first inner leg. The side corresponds to an interface between the TF coil and a second TF coil. The teeth extend along a direction having a component in a radial direction of the tokamak. The teeth are configured to mechanically engage with second teeth of a second inner leg of the second TF coil.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of Provisional Application No. 63 / 301,611, filed January 21, 2022, entitled “STRUCTURE FOR HANDLING INDUCTIVELY PROPAGATING QUENCH IN TOROIDAL MAGNETS,” which is hereby incorporated by reference in its entirety.

[0002] The apparatus and techniques described herein relate to handling asymmetric forces on electromagnets (coils) arranged in a toroidal configuration, and in particular to handling such forces in a tokamak reactor. [Background technology]

[0003] Fusion energy is a possible solution to the need for clean energy. It is safe, energy dense, and produces no greenhouse gas emissions. In a fusion reaction, light atomic nuclei, such as hydrogen, combine to form heavier nuclei, such as helium, producing energy. Summary of the Invention [Means for solving the problem]

[0004] Some aspects relate to a toroidal field (TF) coil for a tokamak. The TF coil includes a first inner leg having teeth on a side of the first inner leg. The side corresponds to an interface between the TF coil and a second TF coil. The teeth extend along a direction having a component in a radial direction of the tokamak. The teeth are configured to mechanically engage with second teeth of a second inner leg of the second TF coil.

[0005] The direction may be the radial direction of the tokamak.

[0006] The direction may additionally have a component in the normal direction of the tokamak.

[0007] The component may be a positive component, and the TF coil may further include a third tooth on a side of the first inner leg extending along a direction having a component in a radial direction of the tokamak and a negative component in a vertical direction of the tokamak.

[0008] The TF coil may have a metal case and the teeth may form a surface of the metal case on a side of the first inner leg.

[0009] The metal case may comprise steel.

[0010] The tines may have a rounded shape.

[0011] The first inner leg may have a third tine on a second side of the first inner leg.

[0012] The tines may be configured to engage with the second tines when the TF coil and the second TF coil are energized.

[0013] Some embodiments relate to a tokamak including a plurality of toroidal field (TF) coils including a first TF coil having a first inner leg having a first tine on a side of the first inner leg, the first tine extending along a direction having a component in a radial direction of the tokamak, and a second TF coil having a second inner leg having a second tine on a side of the second inner leg, the first tine may be configured to mechanically engage with the second tine.

[0014] The direction may be the radial direction of the tokamak.

[0015] The direction may additionally have a component in the normal direction of the tokamak.

[0016] The component may be a positive component, and the first TF coil may further include a third tine on a side of the first inner leg. The third tine may extend along a direction having a component in a radial direction of the tokamak and a negative component in a vertical direction of the tokamak.

[0017] The first TF coil may have a metal case and the first tine may form a surface of the metal case on a side of the first inner leg.

[0018] The metal case may comprise steel.

[0019] The tines may have a rounded shape.

[0020] The first inner leg may have additional teeth on a second side of the first inner leg.

[0021] The first tines may be configured to engage with the second tines when the TF coil and the second TF coil are energized.

[0022] The first inner leg and the second inner leg may be configured to contact the central solenoid when the first and second TF coils are energized.

[0023] The tines or first tines may extend along a side of the first inner leg across most of the vertical extent of the first inner leg.

[0024] Some aspects relate to a method of forming a toroidal field (TF) coil for a tokamak, the method including machining teeth on a side of an inner leg of the TF coil, the teeth extending across a majority of a vertical extent of a first leg, the teeth extending along a direction extending between an inner side of the inner leg and an outer side of the inner leg.

[0025] The inner leg may form part of a metal case of the TF coil. The machining step may comprise machining teeth into the metal case on a side of the inner leg.

[0026] Some aspects relate to a method for partial assembly of a tokamak, the method including positioning a first toroidal field (TF) coil and a second TF coil spaced apart from each other and from a central solenoid structure of the tokamak, where a first tooth of a first inner leg of the first TF coil faces a second tooth of a second inner leg of the second TF coil.

[0027] The method may be performed such that when the first and second TF coils are energized for operation of the tokamak, the first and second teeth engage with one another and the first and second TF coils contact the central solenoid structure.

[0028] The foregoing summary is provided by way of illustration and is not intended to be limiting.

[0029] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component illustrated in various figures is represented by a like numeral. For purposes of clarity, every component may not be labeled in every figure. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a perspective view of a Tokamak fusion reactor. [Diagram 2]FIG. 2 shows a top view of the bucked design of the tokamak when the TF coils are not energized. [Diagram 3] FIG. 3 shows a top view of the backed design of FIG. 2 when the TF coil is energized. [Figure 4] FIG. 2 illustrates multiple TF coils arranged around a central solenoid and having one or more layers of windings. [Figure 5A] 13A-13C show additional details of the internal leg toothing, according to some embodiments. [Figure 5B] 13A-13C show additional details of the internal leg toothing, according to some embodiments. [Figure 5C] FIG. 13 illustrates details of a toothing according to some embodiments. [Figure 5D] FIG. 13 illustrates details of a toothing according to some embodiments. [Figure 6] FIG. 2 shows a view of one example of a TF coil inner leg from the perspective of the central solenoid. [Figure 7A] FIG. 7 is a diagram illustrating a schematic of radially extending teeth as in the example of FIG. 6; [Figure 7B] FIG. 13 is a diagram illustrating another example of teeth having a "herringbone pattern," where the teeth extend along a direction having both radial and vertical components. [Figure 8] FIG. 2 illustrates an assembled TF coil. [Figure 9] FIG. 1 shows the results of a simulation illustrating the stresses produced by significant out of plane deformation of a TF coil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Magnetic confinement is a technique for generating fusion power by using magnetic fields to confine a plasma and create the conditions for the plasma to undergo nuclear fusion. Extremely high plasma temperatures, on the order of 150 million degrees Celsius, are required to initiate the fusion reaction, and the plasma can be heated by the action of magnetic fields and using external heating methods. Magnetic confinement of plasma is challenging because turbulence, instabilities, and other effects within the plasma can rapidly reduce the efficiency of the fusion reaction or even stop it altogether.

[0032] The reactor design known as a tokamak is an approach to magnetic confinement that seeks to address problematic instabilities that can result in the plasma during heating and / or fusion reactions. In a tokamak, the plasma is confined to a toroid, and instabilities in the plasma are controlled by arranging the magnetic field to cause particles of the plasma to transition between the inner and outer sides of the toroid multiple times per revolution. To control the plasma in a tokamak, magnets are used to create toroidal and poloidal fields that define the shape and position of the plasma within the toroid, as well as drive the motion of the plasma around the toroid.

[0033] No previous magnetic confinement fusion device has demonstrated a gain greater than unity, a necessary step to commercialize magnetic confinement fusion devices as a viable energy source. Tokamak fusion performance can be improved by increasing the magnetic field strength or by increasing the size of the tokamak. Increasing the size of the tokamak can require significant infrastructure and lead to high costs. Thus, it would be desirable to keep the size of the tokamak reactor small while increasing the magnetic field to improve performance. Magnets with the ability to achieve high magnetic field strengths have been demonstrated using cryogenically cooled high temperature superconductor (HTS), which can be in the form of HTS tapes.

[0034] FIG. 1 is a perspective view of a tokamak fusion reactor 10 including a vacuum vessel 11. The vacuum vessel 11 is disposed within a radiation shield (or "shielding tank") 41. The vacuum vessel 11 and radiation shield 41 are disposed around a central solenoid 12. Toroidal field (TF) coils 13 are disposed around the vacuum vessel 11. As illustrated, the TF coils 13 may each have a D-shape. Other shapes may be used. The body of the TF coils 13 may be formed from a conductive metal, often in the form of a baseplate having one or more superconducting current paths formed therein from HTS tape. The HTS tape may be wrapped around the body of the baseplate one or more times. Electric current is provided to the HTS coils 13 to generate a high strength magnetic field. The conductive channels through the baseplate may further have conductive material (sometimes referred to as "co-wound") disposed within the baseplate (in addition to the HTS tape). In some embodiments, a conductor may be placed over the HTS as a lid. According to some embodiments, the HTS may comprise a rare earth barium copper oxide superconductor (REBCO), such as yttrium barium copper oxide (YBCO). In some embodiments, the HTS coil 13 may include multiple layers of windings arranged in a stack. In this arrangement, each layer of windings may be referred to as a "pancake," and the stacked layers of windings may be referred to as a "pancake stack."

[0035] The inventors recognize and appreciate the need to handle the large forces that can occur in a tokamak reactor. For example, high magnetic field strengths result in large Lorentz forces on conductors. While forming magnets into high strength metallic structures can stabilize conductors in the presence of static fields, the inventors recognize and appreciate that transient events in a tokamak can create large asymmetric forces on the TF coils 13. One example of such a transient event is a "tsunami" quench that inductively propagates around the tokamak. In a tsunami quench, the transition of one TF coil from a superconducting state to a non-superconducting state creates a change in the magnetic field that affects a neighboring TF coil, which can in turn cause the neighboring TF coils to quench, and the process can continue around the tokamak in a quench "tsunami". Another example of a transient event is during a "shot" where a plasma forms in the vacuum vessel 11. The interaction between the time-varying magnetic fields generated by the central solenoid (CS) with the currents in the TF coils 13 can create so-called out-of-plane (OOP) forces that tend to deform the inner leg 14 of the TF coil (closest to CS 12) in the circumferential direction, tangential to the cylindrical interface between the inner surface of the inner leg 14 and the outer surface of CS 12.

[0036] Such events can create large asymmetric forces on the TF coils 13 that can cause the TF coils 13 to bend and / or twist out of their nominal in-plane shape. Thus, the inventors recognize and appreciate that a need exists for stiffening or otherwise mechanically stabilizing the TF coils 13 to make them robust against transient events.

[0037] During operation of the TF coils 13, their magnetic fields create forces that push the TF coils 13 towards the center of the tokamak. These forces may be addressed by using various approaches. One technique is called "wedging" and sometimes referred to as a "wedged" design. In a wedged design, the TF coils 13 are designed to push against each other as they are pushed inside the tokamak, which distributes the forces from one TF coil to another in the circumferential direction of the tokamak. Another technique is called "bucking" and sometimes referred to as a bucked design. In a bucked design, the TF coils are pushed against a central structure of the tokamak, such as the CS. The two techniques are not mutually exclusive and some designs rely on a combination of both techniques, which may distribute the forces in the circumferential and radial directions in different proportions depending on the design.

[0038] The present inventors have recognized and appreciated that a primarily "backed" design is preferred for creating small Tokamak reactors for several reasons. First, a primarily backed design distributes forces away from the TF coil winding pack and toward the center of the Tokamak, which helps to avoid strain on the windings. Second, a primarily backed design may serve a secondary purpose of countering the expansion forces created by the central solenoid. A primarily backed design helps to avoid the need for containment structures to absorb the expansion forces created by the central solenoid, which helps to keep the size of the Tokamak small.

[0039] Figure 2 shows a top view of the backed design when the TF coils are not energized. As shown in Figure 2, the inner legs 14 of the TF coils are spaced apart from each other and from the CS 12. Figure 3 shows a top view when the TF coils are energized. The inner legs 14 primarily press against the CS 12 as they move inward toward the CS 12, and also against each other.

[0040] Additional details of the TF coil inner leg 14 and its interface with other structures are shown in FIG. 4. As shown in FIG. 4, multiple TF coils are arranged around a central solenoid (CS) 12, with their inner legs 14 in contact with each other. Each TF coil 13 includes one or more layers of windings 210 that extend through the inner legs 14. As shown, the inner legs 14 may have a wedge shape. The one or more layers of windings 210 may be housed within a structural case 212 of the TF coil 13. Between adjacent coils is a TF-to-TF interface 214. Between the inner legs 14 of the TF coil 13 and the CS 12 is a TF-to-CS interface 216 on the inner side of the inner leg 14. The TF-to-TF interface 214 and the TF-to-CS interface 216 may have electrically insulating material that insulates the TF coils 13 from each other and from the CS 12. Such insulation may prevent the formation of eddy currents that may lead to excessive heating. An outer side 217 of each inner leg 14 faces the outer leg of the TF coil (as can be seen in FIG. 1) in the radial direction R of the tokamak.

[0041] As mentioned above, the inventors have recognized and appreciated that there is a need to reinforce or otherwise mechanically stabilize the TF coils to make them robust against transient events. In some embodiments, the inner legs 14 of the TF coils 13 may be designed to press against one another when the TF coils 13 are energized, as shown in FIG. 4, and structures may be located on the surfaces of adjacent TF inner legs that mechanically engage with one another. More specifically, according to some embodiments, the side of the inner leg 14 that faces the inner leg of the adjacent TF coil may have "teeth" at the TF-to-TF interface 214 that extend along the side of the inner leg. When the inner legs of the TF coils 13 are pressed against one another, the teeth of the legs 14 of the adjacent TF coils 13 engage with one another, which provides load sharing between the toroidal field magnets. The teeth may have valleys and crests that extend radially (direction R in FIG. 4) or in a direction having both radial and vertical components (into or out of the page in FIG. 4), as discussed further below.

[0042] 5A and 5B show additional details of the inner leg tines 1 according to some embodiments. The radial dimension in FIG. 4 corresponds to the direction out of the page in FIG. 5A and 5B. The vertical direction V and the circumferential direction C in FIG. 4 are further labeled in FIG. 5A and 5B. As can be seen in FIG. 5A, the case 212 of each inner leg 14 has tines 1 at the interface 214 with the inner leg 14 of the adjacent TF coil 13, which mechanically engage with corresponding tines 1 of the adjacent inner leg 14. The tines 1 have valleys 71 and crests 72 that are complementary to those of the adjacent inner leg 14. The engagement of the tines of the adjacent inner legs 14 helps to absorb and distribute forces, such as those caused by transient events in the tokamak, which may help prevent deformation and vertical movement of the TF coil 13. The teeth 1 may correspond to the sides of the case 212 and may be formed by machining the sides of the case 212. The case 212 may be a forged metal (e.g., steel) that is subsequently machined (e.g., milled) to form the teeth 1. During a plasma "shot," the TF coil 13 may experience large electromagnetic forces that tend to cause the TF-to-TF interface 214 to slip along the sidewall of the TF coil case 212. This slippage is prevented by the engagement of the teeth 1, which restricts the vertical movement of adjacent TF coils past each other. The teeth 1 may also help prevent deformation of the TF coil 12 in the circumferential direction due to transient forces. The radial extension of the teeth 1 allows adjacent TF coils to move relative to each other along the radial direction R, which allows the TF coils to back up more against the CS 12 when they are energized.

[0043] To prevent currents, such as eddy currents, from flowing across the TF-to-TF interface 214, an insulating material 53 may be disposed between teeth 1 of adjacent cases 212. The insulating material 53 may comprise a polymeric material, such as a polyimide material, but is not limited to polyimide or polymeric materials. Because insulating materials can be subject to significant grinding and crushing forces, in some embodiments, the interface structure at the TF-to-TF interface 214 may further comprise one or more metal sheets.

[0044] FIG. 5A shows an example where portions of a pair of TF coil cases 212 may be adjacent to each other across a radial axial surface. As noted above, during plasma generation, the TF coils experience large electromagnetic forces that tend to cause slippage along the sidewalls of the TF coil case. This slippage may be suppressed by forming the sidewalls of the TF case 212 as teeth 1, as shown in FIG. 5A. To prevent a continuous electrically conductive loop from being formed by the TF case around all the TF coils, and consequently high-resistance heating caused by vortices induced in this loop by the time-varying fields from the CS and PF coils, an interface structure 50 may be disposed between at least a portion of the teeth 1 of the TF coil case 212 at the TF-to-TF interface 214. In an embodiment, the interface structure 50 may be deposited, attached, or otherwise disposed on at least a portion of the surface of one or more TF coil case teeth 1. In an embodiment, the interface structure 50 may be provided, mounted, or otherwise disposed as a separate corrugated sheet between the TF coil teeth 1.

[0045] 5A shows an example in which interface structure 50 comprises insulating materials 51 and 52 (e.g., may be provided as insulating sheets of material such as anodized metal, such as an anodized metal sheet) positioned or otherwise disposed on either side of metal material 53. In an embodiment, insulating materials 51 and 52 and metal material 53 may be stacked to provide interface structure 50 as a stacked insulator. Insulating materials 51 and 52 and metal material 53 are disposed between tines 1. Thus, tines 1 may be in contact with insulating materials (e.g., insulating sheets 51 and / or 52).

[0046] 5B shows an example in which the interface structure 50 comprises a metal sheet 53 located or otherwise disposed on one surface of an insulating material 51. In this embodiment, the opposite surface of the insulating material 51 is in direct contact with the tooth 1.

[0047] In other embodiments, the TF-to-TF interface 214 may include additional layers of insulating material and / or metal sheets. In some embodiments, if the insulating material 51 / 52 is sufficiently robust, the TF-to-TF interface 214 may not include metal sheets. Instead, the insulating material 51 / 52 may contact tooth 1 on both TF cases 212, for example.

[0048] The insulating material 51 / 52 may be provided in any suitable thickness, for example, from 0.01 mm to 1 mm, such as 0.1 mm. The insulating material 51 / 52 may have a suitable standoff voltage, for example, greater than 1 V, greater than 10 V, or greater than 100 V or 1 kV. As noted above, the insulating material (e.g., insulating material 51) may be provided from one or more insulating sheets. At least some or all of the one or more sheets may have any suitable thickness, for example, from 0.01 mm to 1 mm, such as 0.1 mm. Furthermore, some or all of the insulating sheets may have a suitable standoff voltage, for example, greater than 1 V, greater than 10 V, or greater than 100 V or 1 kV. However, these are examples and the insulating material is not limited to a particular thickness or standoff voltage.

[0049] The one or more metal sheets 53 may each have a thickness ranging between about 0.1 mm and about 2.0 mm, or 25-50 microns, in some cases. However, these are examples and the metal sheets are not limited to any particular thickness. In some embodiments, layer 53 may be provided as an insulating material.

[0050] The tines 1 may be designed to take into account both the tensile loads and the local shear forces at the inner leg 14. In one particular design, the tines may have a 45 degree included angle, a 44.87 mm pitch, and a 16.96 mm depth, as illustrated in FIG. 5C. The tines 1 may have an elliptical profile with a major radius of 11 mm and a minor radius of 5.5 mm (2:1 aspect ratio), as shown in FIG. 5D. The ellipse rotates relative to the inner leg, forcing the tine walls to maintain contact with the included angle and at the tooth valleys. However, this is an example, and the tines 1 may have different included angles, pitches, depths, profiles, or shapes, as the structures and techniques described herein are not limited in this regard.

[0051] FIG. 6 shows a perspective view of one example of the TF coil inner leg 14 from the perspective of the view looking out from the CS 12. As can be seen from FIG. 6, the two sides of the inner leg 14 facing the adjacent TF coil inner leg have teeth 1 extending in the radial direction. In this example, the teeth 1 extend in the radial direction and do not have any components extending in the vertical direction. FIG. 6 further illustrates that the teeth 1 can be formed over a large part of the surface of the TF-to-TF interface 214. In this example, the teeth 1 extend over an area corresponding to the vertical extent of a straight (e.g., not curved) part of the inner leg 14. Furthermore, the teeth can extend over the entire radial extent of the TF-to-TF interface or over a large part of the entire radial extent. However, the teeth 1 can extend over a larger or smaller extent in the vertical and / or radial directions.

[0052] Fig. 7A illustrates diagrammatically a radially extending toothing 1a, like the example of Fig. 6. The valleys 71 and crests 72 of the toothing 1a extend horizontally in Fig. 7A along the radial direction R and have no component in the vertical direction V. A CS 12 is also shown on the inside of the inner leg 14.

[0053] FIG. 7B illustrates another example of teeth 1b with a "herringbone pattern," in which teeth 1b extend along a direction having both radial and vertical components. In the upper half of FIG. 7B, which corresponds to the upper half of the inner leg 14, the valleys 71 and crests 72 of teeth 1b extend in a direction having both a vertical component upward and a radial component. In the lower half of FIG. 7B, which corresponds to the lower half of the inner leg 14, the valleys 71 and crests 72 of teeth extend in a direction having both a vertical component downward and a radial component. As previously described with respect to radial teeth, the teeth in the herringbone pattern may be configured to mechanically engage complementary teeth on adjacent inner legs. Providing teeth with a herringbone pattern may constrain both vertical and horizontal slippage of adjacent TF coils.

[0054] The assembled TF coil 13 is illustrated in FIG. 8. The load relief features include TF coil inner leg teeth 1, radial shear keys 2a and 2b in an elliptical arc connecting the inner and outer legs of the TF coil 13, inner inter-coil structures 3a and 3b, and outer inter-coil structures 4a and 4b. The radial shear keys may be insertable keys with a rectangular cross section. The inner and outer inter-coil structures are symmetrical top to bottom, with upper and lower assemblies. Both sets of inter-coil structures include inner and outer plates connected by radial plates.

[0055] The system integration sites include the structural interface 5 with the central solenoid 12, including the "backing region", mounting points 6a-6h for the poloidal field (PF) coils, including mounting points PF1 upper 6a, PF2 upper 6b, PF3 upper 6c, PF4 upper 6d, PF4 lower 6e, PF3 lower 6f, PF2 lower 6g, and PF1 lower 6h, gravity support 7 for the vacuum vessel, gravity support 8 for the TF coils and attached subsystems, mountings for the divertor coils at 9a and 9b, connections 80a-80b to the cryogenic cooling distribution system, connections 81 to the electrical feed and inter-magnet electrical connections, and connections 82 to the error field correction coils. All system integration features may be welded to the Inner Poloidal Ring and Outer Poloidal Assembly prior to final assembly and welding of the TF coils 13.

[0056] Radial and normal forces and bending (in-plane loads) with respect to the toroidal axis are relieved by the backing provided by the "bulk" of the TF coil 13 and its interface with the central solenoid 12. The in-plane loads are manifested as membrane, bending, and contact forces within the TF coil 13. Relief of radial forces on the TF coil 13 by backing versus wedging creates a more favorable effective stress state that is compatible with existing structural engineering materials. The inner leg teeth 1 facilitate a backed design since localized features are needed on the inner leg to interrupt the loads. The cross-sectional thickness of the TF coil 13 is designed to withstand the remainder and majority of the membrane and bending loads. The toroidal forces are not relieved by the bulk structure of the toroidal magnet, nor by the backing pressure of the central solenoid. The load relief features 1-4b are primarily responsible for this, as well as the distribution of localized dynamic in-plane load differences to neighboring magnets.

[0057] The inner leg teeth 1 provide a vertical load distribution between neighboring TF coils 13. They serve to limit the displacement and distortion of the coils where the current peaks, and the two adjacent coils of that coil are close to the nominal current, resulting in a significantly reduced current. Assuming uniform tooth spacing, clearance, and tolerances, the tooth engagement due to local differences in the vertical load in the inner leg is most pronounced at the "top" and "bottom" of the inner leg. As a result, high toroidal vertical shear forces and stresses are observed in this region of active tooth engagement. The cross-sectional thickness of the inner leg of the TF coil 13 can be designed taking these shear forces into account. Here, the TF coil 13 windings are "bent" and follow a circular arc to provide additional cross-sectional thickness in the area of ​​greater bending than at the mid-plane of the inner leg. Due to the large radial displacement of the inner leg resulting from the imbalance of radial loads on the central solenoid, the inner leg radial teeth also positively engage near the inner leg vertical midplane. Engagement in the region of the inner leg vertical midplane increases the effective bending stiffness about the radial and toroidal axes and limits the toroidal and radial displacement of the inner leg. The tooth clearance and tolerances may be designed with this in mind to define the interface requirements at the interface with the central solenoid 12.

[0058] The radial shear keys 2a and 2b provide radial load distribution between neighboring coils and primarily serve to maintain the "round" shape of the TF coil 13 during transient events such as inductively coupled quenches. The keys closest to the inner leg radial leg also serve to provide vertical load distribution and contribute to the high shear forces observed at the top and bottom of the inner leg.

[0059] The inner inter-coil structure, features 3a and 3b, and the outer inter-coil structure, features 4a and 4b, transfer unbalanced toroidal forces to neighboring coils. The inner and outer inter-coil structures also serve to transfer radial and vertical loads, respectively, between neighboring TF coils 13. These forces are compressive and are transferred by insertable shear pins. Each pin can be loaded in double shear. Radial pieces or plates connect the inner and outer plates of the inner and outer inter-coil structures, reducing bending loads on the plates themselves and on the pins. The plates are held in place by bolts that transfer negligible toroidal loads compared to the much larger pins.

[0060] One notable characteristic of the interface connection systems with the TF coils 13 is their displacement compatibility. The central solenoid 12 and interfaces with the TF coils 13 accommodate the radial displacement of the TF coils 13. The interfaces with the poloidal magnets, features 6a-6h; gravity support for the vacuum vessel, feature 7; divertor coil magnets, features 9a and 9b; connections to the cryogenic cooling distribution system 10a-10b; connections to the electrical feed and intermagnet electrical connections 11; and connections to the error field correction coils 12 accommodate the toroidal displacement of the TF coils 13 and the vertical and radial expansion differences between neighboring structures through the use of flexible mounts and joints. Similarly, but to a lesser extent, the vacuum vessel gravity support, feature (8), also accommodates the toroidal displacement of the magnets and the differences in radial and vertical displacement between adjacent magnets.

[0061] 9 shows the results of a simulation illustrating the stresses produced by a significant out-of-plane deformation of the TF coil 13. The teeth 1 help to absorb the stresses and transfer them to neighboring TF coils (not shown) by the engagement of the teeth 1 with the adjacent TF coils.

[0062] Although several embodiments of the concepts described herein have been described and illustrated herein, those skilled in the art will readily envision various other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the concepts described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are intended to be exemplary, and that the actual parameters, dimensions, materials, and / or configurations will depend on the particular application or applications in which the teachings of the concepts described herein are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the concepts described herein. Thus, it should be understood that the foregoing embodiments are presented merely as examples, and that within the scope of the appended claims and equivalents thereto, the described concepts may be practiced other than as specifically described and claimed. The concepts described herein relate to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kit, and / or methods is included within the scope of the concepts described herein, provided that such features, systems, articles, materials, kit, and / or methods are not mutually inconsistent.

[0063] In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and / or inconsistent disclosure with respect to each other, the document having the later effective date shall control.

[0064] All definitions, as defined and used herein, should be understood to take precedence over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meaning of the defined term.

[0065] The indefinite articles "a" and "an," as used herein and in the claims, unless expressly indicated otherwise, should be understood to mean "at least one."

[0066] The phrase "and / or," as used herein and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctive in some cases and disjunctive in other cases. Multiple elements recited by "and / or" should be interpreted in the same manner, i.e., "one or more" of the elements so conjoined. Other elements other than the elements specifically identified by the "and / or" clause may optionally be present, whether associated or unassociated with those elements specifically identified. Thus, as a non-limiting example, a reference to "A and / or B," when used in conjunction with open-ended language such as "comprising," may refer in one embodiment to only A (optionally including elements other than B), in another embodiment to only B (optionally including elements other than A), in yet another embodiment to both A and B (optionally including other elements), and so forth.

[0067] As used herein and in the claims, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" shall be interpreted as inclusive, i.e., including at least one of the elements or list of elements, and optionally additional unlisted items, but also including two or more of the elements or list of elements, and optionally additional unlisted items. Only terms clearly indicating otherwise, such as "only one of" or "exactly one of," or "consisting of" when used in the claims, shall refer to the inclusion of exactly one element of the elements or list of elements. In general, the term "or" as used herein, when preceded by a term of exclusivity, such as "either," "one of," "only one of," or "exactly one of," shall be interpreted simply as indicating an exclusive alternative (i.e., "one or the other, but not both").

[0068] As used herein and in the claims, the phrase "at least one" in reference to a list of one or more elements should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed in the list of elements, and not excluding any combinations of elements in the list of elements. This definition further recognizes that elements other than those specifically identified in the list of elements to which the phrase "at least one" refers may optionally be present, whether associated or unassociated with those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B" or, equivalently, "at least one of A and / or B") can refer in one embodiment to at least one A, optionally including more than one, with no B (and optionally including elements other than B), in another embodiment to at least one B, optionally including more than one, with no A (and optionally including elements other than A), in yet another embodiment to at least one A, optionally including more than one, and at least one B (and optionally including other elements), optionally including more than one, and so forth.

[0069] When the word "about" is used herein in reference to a number, it should be understood that yet other embodiments may include that number unmodified by the presence of the word "about."

[0070] It should be further understood that, unless expressly indicated otherwise, in any method claimed herein that includes two or more steps or actions, the order of the method steps or actions is not necessarily limited to the order in which the method steps or actions are recited.

[0071] In the claims, and in the preceding specification, all transitional phrases such as "comprising," "including," "having," "having," "containing," "essentially including," "holding," "composed of," and the like, are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively.

Claims

1. 1. A toroidal field (TF) coil for a tokamak, comprising:

1. A TF coil comprising: a first inner leg having teeth on a side of the first inner leg, the side corresponding to an interface between the TF coil and a second TF coil, the teeth extending along a direction having a component in a radial direction of the tokamak, the teeth configured to mechanically engage with second teeth of a second inner leg of the second TF coil.

2. TF coil according to claim 1 , wherein the direction is a radial direction of the tokamak.

3. TF coil according to claim 1 , wherein the direction additionally has a component in the vertical direction of the tokamak.

4. 4. The TF coil of claim 3, wherein the component is a positive component, the TF coil further comprising a third tooth on the side of the first inner leg extending along a direction having a component in a radial direction of the tokamak and a negative component in the vertical direction of the tokamak.

5. 5. A TF coil as claimed in claim 1, wherein the TF coil has a metal case, the teeth forming a surface of the metal case at the side of the first inner leg.

6. The TF coil of claim 5 , wherein the metal case comprises steel.

7. 7. A TF coil as claimed in claim 1, wherein the teeth have a rounded shape.

8. 8. A TF coil as claimed in claim 1, wherein the first inner leg has a third tooth on a second side of the first inner leg.

9. 9. A TF coil as claimed in claim 1, wherein the teeth are configured to engage with the second teeth when the TF coil and the second TF coil are energised.

10. It is a tokamak, a plurality of toroidal field (TF) coils, the plurality of TF coils comprising: a first TF coil having a first inner leg having a first tooth on a side of the first inner leg, the first tooth extending along a direction having a component in a radial direction of the tokamak; a second TF coil having a second inner leg, the second inner leg having a second tooth on a side of the second inner leg; Including, The tokamak, wherein the first tines are configured to mechanically engage the second tines.

11. The tokamak of claim 10 , wherein the direction is a radial direction of the tokamak.

12. The tokamak of claim 10 , wherein the direction additionally has a component in a normal direction of the tokamak.

13. 13. The tokamak of claim 12, wherein the component is a positive component, the first TF coil further comprising a third tine on the side of the first inner leg, the third tine extending along a direction having a component in a radial direction of the tokamak and a negative component in the vertical direction of the tokamak.

14. 14. The tokamak of claim 10, wherein the first TF coil has a metal case, and the first tine forms a surface of the metal case at the side of the first inner leg.

15. The tokamak of claim 14 , wherein the metal casing comprises steel.

16. A tokamak as claimed in any of claims 10 to 15, wherein the tines have a rounded shape.

17. 17. The tokamak of any of claims 10 to 16, wherein the first inner leg has an additional tooth on a second side of the first inner leg.

18. 18. The tokamak of any of claims 10 to 17, wherein the first tines are configured to engage with the second tines when the TF coil and the second TF coil are energized.

19. 19. The tokamak of any of claims 10 to 18, wherein the first inner leg and the second inner leg are configured to contact a central solenoid when the first and second TF coils are energized.

20. 20. A tokamak or TF coil as claimed in any preceding claim, wherein the tine or first tine extends along the side of the first inner leg over most of the vertical extent of the first inner leg.

21. 1. A method of forming a toroidal field (TF) coil for a tokamak, comprising the steps of:

11. A method comprising the step of machining teeth on a side of an inner leg of the TF coil, the teeth extending across most of the vertical extent of the first leg, the teeth extending along a direction extending between an inner side of the inner leg and an outer side of the inner leg.

22. 22. The method of claim 21 , wherein the inner leg forms part of a metal case of the TF coil, and the machining step comprises machining the teeth into the metal case at the side of the inner leg.

23. 1. A method for partial assembly of a tokamak, comprising the steps of:

1. A method comprising: positioning a first toroidal field (TF) coil and a second TF coil so that they are spaced apart from each other and from a central solenoid structure of the tokamak, wherein a first tooth of a first inner leg of the first TF coil faces a second tooth of a second inner leg of the second TF coil.

24. 24. The method of claim 23, wherein the method is performed such that when the first and second TF coils are energized for operation of the tokamak, the first and second tines engage with each other and the first and second TF coils contact the central solenoid structure.

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