Work on power from fusion has over the past decade or so moved from the realm of purely plasma physics research to active consideration of concepts of complete fusion reactor systems (1–8). The undertaking of such excercises highlights the technological and engineering problems which must be overcome if fusion power is to become a reality. A major problem to be faced with fusion is that of radiation damage to materials used in the construction of the fusion reactor. Materials damage in a nuclear device is of course not a new topic, as it has been part and parcel of nuclear power since the earliest days of fission reactors (9). However, with fusion reactors far greater demands will be made of materials in terms of radiation loading than have ever been encountered with fission. Although proposals have been made for inertially confined plasmas (10–11), the vast majority of reactor designs to date employ the principle of magnetic confinement, and this demands the incorporation of electrical insulating materials in the structure of the reactor.

Cryogenic electrical tests on tokamak insulation system

Electrical Insulation and Fusion Reactors

The forced flow Nb 3 Sn magnet concept developed by Westinghouse in cooperation with the Oak Ridge National Laboratory offers the fusion program the option of a reactor size superconducting toroidal field coil which has the capability of achieving peak fields of 12 tesla. The Westinghouse LCP coil concept offers a number of advantages besides high field capability. The coil is fabricated by winding stainless-steel-jacketed conductors into machined slots in the structural plates. This configuration provides positive conductor support and prevents accumulation of magnetic loading on individual conductors. Another advantage of this concept is the distribution of the conductors which results in more uniform current density in the overall coil cross-section. This distributed winding approach also provides higher fields on the plasma axis for given peak fields on the conductor. The distributed structure uniformly distributes eddy current losses and has lower losses than lumped structure concepts when subjected to the pulsed poloidal fields. The higher current densities possible, due to more efficient utilization of space coupled with the use of materials with good radiation properties (materials used for the Westinghouse LCP coil), allows for reduction in reactor size, which can be a substantial cost advantage. The modular concept of the Westinghouse coil allows for parallel manufacturing operations. The maintainability and repairability aspects of the coil are also discussed.

Cryogenic electrical tests on tokamak insulation system

Citations

Electrical Insulation and Fusion Reactors

Advantages of the distributed structure concept of the Westinghouse LCP coil design-II

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Advances in cryogenic engineering. Volume 27 - Proceedings of the Cryogenic Engineering Conference, San Diego, CA, August 11-14, 1981