Dual barrier for the suppression of residual resistance degradation in chrome-plated niobium-tin strands

For large fusion magnet applications it has been suggested that the Nb/sub 3/Sn superconductor strand be chrome plated to reduce the sintering tendency and to increase the electrical resistance between the strands. Unfortunately, this chrome plating appears to degrade the RRR after the reaction heat treatment. In addition to the normal Nb/sub 3/Sn material with a barrier separating the copper stabilizer from the rest of the conductor, materials have been made with a second barrier close to the surface. One had 10% and the other 20% by volume of copper on the outside of this external barrier. The variation of the RRR of chrome-plated lengths of these material has been explored for a range of different heat treatments and their significance to TPX and ITER magnets is discussed.<>