Economics of large superconducting toroidal magnets for fusion reactors

Abstract

The encouraging results over the last few years in plasma research have generated renewed optimism that fusion feasibility will be demonstrated in the coming decade. Assuming that such is the case, the next logical step is the construction of a prototype power reactor. If this reactor employs plasma containment by intense magnetic fields, it is highly likely that superconducting magnets will be required for economic reasons. We have previously performed a study on the engineering design of a large superconducting magnet system in a toroidal geometry. In this study, we considered a toroidal field B ₀ = 37 kG, a maximum field at the windings B _max = 80 kG, a major radius of R = 10.5 m, and a minor coil radius r = 5.6 m, in a design using cryostatic stabilization of NbTi with copper. The design resulted in a magnet system with stored energy of 4 x 10 ¹⁰ J requiring 4.75 x 10 ⁸ ft of composite NbTi conductor. The total weight of the system including conductor, stainless steel interleaving, bobbin, bobbin reinforcement, and central compression ring was about 9,025 tons and the total cost was $70,500,000. The cost breakdown of the major components is: compoundmore » conductor, 37%; structural reinforcements, 32%; winding, 13%; bobbins, and refrigeration, 4%. A schematic view of a 5000 MW(th) tokamak fusion power reactor incorporating such a magnet system is shown. In this paper, work is extended and general formulas are developed for arbitrary B ₀, R, and r, for each of the cost items considered in the study, and the total costs determined for a variety of fields and sizes. Although not as accurate as a detailed study, the general formula developed will be useful for quickly estimating the cost of any similar toroidal system subject to the constraint B _max ≤ 85 kG. The cost for any system is found to be proportional to the 4/5 power of the stored magnetic energy. « less

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