Patent Number: 045308128
Section: description

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawing. FIG. 1A is a plane view of a typical segmented coil in accordance with the present invention. Segment 10 of the TF coil 21 is preferably made of copper or copper alloy and is located on the side of the TF coil closest to the main axis 13 of the TFR. Preferably, the segment 11 is made of aluminum or aluminum alloy and is located on the side of the TF coil furthest from the main axis 13 of the TFR. Region 22 in FIG. 1A is the toroidal plasma region The segments 10 and 11 of the coil 21 are joined at joint 12 which is more fully described in connection with FIGS. 2A-C, 3 and 4 below. As can best be appreciated from FIG. 1B, TF coil 21 is only one of a plurality of TF coils that together form the TF generating means 20. The TF coils 21 are insulated from each other with a layer of insulation 19. Preferably, in the region where the adjacent TF coils are in physical contact with each other, (on the side closest to the major axis of the TFR), the layer of insulation is the only material separating the adjacent TF coil windings. It should be understood that in accordance with one aspect of this invention, the blanket means 23 and the shielding means 26 are positioned radially outside of the TF coils 21 from the plasma fusion region 22 and as will be appreciated by one of skill in the art, the blanket may contain a region 24 for breeding tritium as fuel for fusion reactors and/or a region 25 for breeding fissile fuel for fission reactors. The blanket means is also heated by nuclear heating caused by fusion neutrons from the fusion reactions which may occur in the fusion plasma region 22. The blanket means is cooled with coolant from feed line 27, which passes through coolant channels 29 in the blanket and to the coolant return line 28. The TF coils are also cooled with coolant from feed line 30, through TF coolant channels 32 and to the coolant return line 31. Coolant means for the TF coils and blanket are well known in the art and do not form a part of the instant invention. Applicants have found that the joints 12 between the coil segments 10 and 11 must preferably meet the following requirements: 1. Preferably, their mechanical strength in tension and their fatigue endurance must be as great or nearly as great, as that of the weaker of the two metals (aluminum in this case). 2. Preferably, their electrical resistance must be sufficiently small that they are not excessively heated by I.sup.2 R losses. 3. Preferably, they must be sufficiently compact to fit the geometry of the XBTFR. More particularly, they must not protrude from the broad sides of the conductor segments or from the inner edge of the segments facing the plasma fusion region. 4. Preferably, they must not interfere with the removal of heat from the TF coils in their vicinity by the cooling system. Applicants have found that the preferable types of joints that meet these requirements are mechanical joints and metallurgical joints. As will be apparent to one of skill in the art, the metallurgical joints may preferably include soldered joints, brazed joints, fusion welded joints or solid state bonded joints. Preferably, in the case of a mechanical joint, the contact area of the joint is much larger than the cross-sectional area of the conductor segments so as to minimize the electrical resistance of the joint. In accordance with the present invention, the joints can be formed parallel to the face 33 of the TF coils 21 as in FIGS. 2A-2C or they can be in the broad plane 34 of the TF coils 21 as shown in FIG. 3 and FIG. 4. It should be understood that any of the joints formed in accordance with the present invention can be formed either parallel to the face 33 of the TF coil 21 or in the broad plane 34 of the TF coil 21. Preferably, one way to achieve the necessary mechanical joint is depicted in FIG. 2A. The joint consists of an angled lap joint 12A held together by one or more fastening means 15, preferably screws. An angled lap joint can alternately be formed in the broad plane 34 of the TF coil 21. This joint will, with sufficiently large clamping pressure, achieve the necessary low electrical resistance. The tensile stresses of the joint are transmitted by friction between the contacting surfaces 35 and 36 and by the shearing force on the fastening means 15. Alternately, the facing surfaces 37 and 38 can be serrated as depicted in FIG. 2B with serrations formed of alternating positive and negative angular surfaces. Of course, it should be understood that the angles of the adjacent surfaces forming the serrations can be varied over any amount desired and the angle of the serration need not remain constant throughout the length of the joint. It should also be appreciated that adjacent legs along the serrated surface need not be of equal length but can be different. Preferably, however, the facing surfaces 37 and 38 are negative images of each other to provide good contact mating. In FIG. 2C a variation on the serrated surface of FIG. 2B is depicted wherein one side of each pair of angled surfaces forming the serrations has a portion 41 vertical to the broad plane of the TF coil 21 and an angled portion 40 that extends between consecutive vertical portions. Preferably, the joints 12 should be located in a portion of the coil 21 where adjacent coils are separated only by a layer of insulation 18. In those locations the magnetic forces will act to compress the joint thereby reducing the number and size of the fasteners needed to provide the requisite compressive load. It will be apparent to one skilled in the art that the serrated joints described above and depicted in FIGS. 2B and 2C can alternately be placed in the broad plane 34 of the conductors. As depicted in FIGS. 3 and 4, and as discussed above, the joints 12D (in FIG. 3) and 12E (in FIG. 4) may also preferably be positioned in the broad plane 34 of the coil winding as opposed to the joints illustrated in FIGS. 2A, 2B and 2C wherein the joints were positioned parallel to the winding face 33. In the embodiment of FIG. 3, the tensile load on the coil winding 21 is carried by the interlocking teeth 43, the fastening means 16 serving simply to hold the conductor portions in the correct relative orientation. The fastening means 16 may preferably constitute countersunk screw or bolt members that are configured so as not to protrude outside of the smooth contour of the TF coil 21. The contact force required for good electrical conductance is provided by the tensile force, transmitted as a compressive load, across the interlocking tooth surfaces 43. Depicted in FIG. 4 is an alternate embodiment of the interlocking tooth joint. In the embodiment of FIG. 4, the joint is again positioned in the broad plane 34 of the TF coils and preferably is positioned so as to traverse the TF coil 21 generally along a radius of the coil. As a fastening means, a tapered pin 17 may be used, the pin tapering inward toward the inner face of the TF coil 21. In this embodiment, it will be understood by one of skill in the art, both the tensile and compressive contact load are carried by shearing forces in the tapered pin. Several metallurgical fabrication processes may preferably be used to achieve suitable joints 12 for the TF coils 21. It has been found that suitable joints may be formed by one or more of the following processes: welding; including but not limited to gas-metal arc welding; gas-tungsten arc welding; plasma arc welding; shielded metal arc welding; electron beam or laser beam fusion welding; seam or flash resistance welding; bonding, including but not limited to pressure, diffusion, explosive, ultrasonic, magnetic, friction or roll bonding; soldering or brazing using filler metals. In the case of a metallurgical joint, the electrical resistence of the joint will be no greater than that of the parent metals, thus as will be understood, it is not necessary for electrical conduction reasons that the joints have a large contact area. However, as will be readily appreciated by the artisan, a relatively small surface area joint may be mechanically weaker than the parent metals. Therefore, it is preferable to use a large area joint, such as the lap joint of FIG. 2A or such other large area joints as this description will suggest to the artisan, to spread the mechanical load over an area much larger than the cross-sections of the TF coil, thereby reducing the local stress on the joint. Of course, it should be understood that with a metallurgical joint, the fastening means, which may preferably be countersunk screws as illustrated in FIGS. 2A-2C, could be dispensed with. Of course, in the case of the large area interlocking tooth joint that utilizes a tapered pin such as that depicted in FIG. 4, the tapered pin could be eliminated if a metallurgical joint were formed. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifictions and variations are possible in light of the above teaching. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.