Properties of Internal-Tin Nb3Sn Strand for the International Thermonuclear Experimental Reactor
We report on the design and properties of a Nb3Sn wire strand developed for the International Thermonuclear Experimental Reactor (ITER). The internal-tin process was employed using 19 subelements, 6 spacers, and a Ta-containing barrier to separate the superconducting core from the Cu stabilizer. Specific values of the four properties — critical current density Jc, hysteresis losses, residual resistivity ratio RRR, and piece length — required by the ITER specification are difficult to achieve simultaneously in one strand design. This is particularly true when the strand is Cr plated to prevent sintering and to provide interstrand resistance. Some aspects of conductor design and heat treatment, and how these affect the various properties, including n value, are outlined.
KeywordsCritical Current Density Ramp Rate Hysteresis Loss International Thermonuclear Experimental Reactor High Density Material
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