Patent Number: 046577238
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. In FIG. 1, there is depicted a tokamak reactor 100 having a TF coil assembly 10 surrounding a toroidal plasma region 20 having a toroidal axis 25. For purposes of illustration, the ohmic heating transformer coil 30 is shown disposed about a central axis 45 and located coaxially interior to the TF coil assembly 10. The tokamak core is located within a vacuum chamber 40 and as will be appreciated by one of skill in the art, has several poloidal field coils 50 in addition to the ohmic heating coil 30 which perform various necessary functions to confine, heat, locate and stabilize the plasma in the plasma region 20. The TF coil means 10 are energized by a power source (not shown) which forms no part of the instant invention, but which when operating causes very large current densitites to flow through the toroidal field coil turns. These high current densities cause Joule heating to occur in the toroidal field coil assembly. In addition, during operation, the plasma in the plasma region 20 radiates both thermal heat and energetic neutrons; the energetic neutrons being an additional source of heat. Because of the above-referenced heating effects, it is necessary to cool the TF coil turns. However, the coils must be cooled in such a manner as to take into account the problem of pressure drop and flow distribution. In addition, the cooling arrangement must not create an excessive void fraction in the TF coil or create excessive material stresses or hot spots associated with getting coolant into and out of each turn of the toroidal field coil. Turning to FIGS. 2, 3 and 4, it can be seen that the TF coil turns are composed of generally flat washer-like disks 11 and 12 joined at a joint 31. The disks have a relatively narrow thickness along the edge 37 as compared to the flat faces 34 and 36. Each coil has a leading end and a trailing end as indicated by numerals 33 and 32, respectively, for coils 12 and 11, respectively. The trailing end 32 of coil 11 is joined at joint 31 with the leading end 33 of coil 12. It is in this manner that the toroidal field coil assembly 10 as shown in FIG. 1 is formed. It will be appreciated by the artisan that in the compact TF coil assembly of the present invention, to provide coolant supply and return headers inside the body of the coil material which were wide enough to allow for coolant flow without unduly high pressure drop and high velocity, would create a void in the TF coil material of such magnitude as to cause electric current bunching in the region of the header (thus creating unduly large I.sup.2 R losses) in addition to very high material stresses. Therefore, in accordance with the present invention, the coolant supply header 19 and coolant return header 17 are positioned along the flat sides 36 and 34 of the TF coil turns 12 and 11, respectively. These headers are positioned just above and below the joint 31. The coolant channels 13 bend outward in the vicinity of the headers 19 and 17 to form inlet openings 21 and outlet openings 16 which, as seen in FIG. 4, are arranged radially to the axis of the tokamak. The general area of the bends is indicated in FIG. 3 by numerals 15 and 22. While the inlet and outlet openings are indicated in FIG. 4 to be rectangular, it will be appreciated by the artisan that they can be circular, elliptical, square or other convenient geometric shapes. The distribution of coolant flowing through the individual coolant channels within each coil turn is affected by the relative pressure drops in the channels and by the pressure drop characteristics of the supply and return headers. Therefore, as shown in FIG. 4, it may be necessary to taper the headers, especially the supply header, so that the flow area decreases, with decreasing radial location from the axis of the tokamak. Tapering the headers also may be desirable in order to maintain clearance between the header and the adjacent TF coil turn. Because the coolant channels 13 bend outward to meet the header structures above and below the joint 31, the present invention avoids the creation of a large void in the region of the joint 31 and the attendant current bunching and high-stress situations. The headers may preferably be cut from round tubes, sections of which are then cut out to conform to the TF coil turns and attached by welding or brazing to the TF coils in such a manner as to enclose the coolant channel inlet and outlet openings. Since the header structure can be welded or brazed to the coil turn after each turn is machined, the fabrication of the coil turn is simplified. In addition, it should be appreciated that while the inlet and outlet header structure depicted is circular, it can alternatively be made of any convenient geometric shape such as elliptical, square or rectangular or can be conformed to accommodate space limitations between turns. Another embodiment of this invention is shown in FIG. 5. TF coil turns 101, 102 and 103 having coolant channels 104 are served by common supply and return headers 105 and 106, respectively, that overlap the joint 107. For this configuration, the coolant flow direction within the coolant channels may preferably alternate from one TF coil turn to the next. This embodiment has the advantages of a uniform temperature within the region of the joint and it halves the required number of headers from, for example, the embodiment of FIG. 3. In the embodiments shown in FIGS. 2, 3, 4, and 5, the coolant flows into the coil turn at one location, flows all the way around the coil turn picking up heat and then flows out at another location. While the embodiments described above have many useful advantages, it will be understood by the artisan that there will exist a substantial variation in the bulk temperature of the coil turn in the direction of coolant flow, i.e., the turn will be at a higher temperature near its coolant outlet than at its coolant inlet. As explained hereinabove, this gives rise to several undesirable characteristics such as high maximum coil temperatures, lower coil strength, deflections and stresses. Turning to FIGS. 6 and 7, side supply headers 49 are positioned on both sides of a joint 50 between adjacent coil turns 56 and 57. As best seen in FIG. 7, each supply header 49 supplies every other coolant channel 55 and each return header 59, services every other coolant channel 52. The result is a cooling arrangement where within each turn of the coil the cooling channels alternate with respect to the direction of coolant flow. Therefore, at any circumferential location around a coil turn, a cut across the coil would yield approximately the same average coil material temperature for the material surrounding two adjacent cooling channels. An additional embodiment requiring only half the number of headers and connections is depicted in FIGS. 8 and 9 wherein a single header is used which overlaps the joint between two coil turns, thus serving both turns simultaneously. Turning now to FIGS. 8 and 9, there is depicted a single supply header, 35 which covers the coolant inlet openings 21 in two adjacent coils 60 and 61. Of course, it should be understood in this embodiment that in alternate coolant channels, coolant flows in the same direction but in adjacent coolant channels, coolant flows in opposite directions. Likewise, return header 36 is positioned to cover joint 31 and outlet openings 16. In this manner, fewer components can be used to construct the cooling arrangement thereby simplifying even further the fabrication of the TF coil. In operation, coolant is flowed from an external source and through a manifold into the supply header. It travels along the supply header which is of a controlled shape so as to achieve proper coolant distribution, pressure drop and flow velocity and into coolant inlet openings 21. The coolant then flows through the bend portion 22 of the coolant channel, through the coolant channel 13. As illustrated in the adjacent coil 61, coolant then flows through the bend portion 15 of the coolant channel and to the outlet of the coolant channel 16 located on the flat face of the TF coil turn. The coolant then flows along the flat face of the TF coil turn, through the return header 36 back to the coolant source through a manifold (not shown) which forms no part of the instant invention. TF coil assemblies built in accordance with this invention are of simplified design and manufacture, and produce good thermal and hydraulic properties with regard to coolant flow. 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 modifications and variations are possible in light of the above teaching. The embodiments were 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.