Test results for a Nb3Sn dipole magnet

A cosine theta type dipole magnet using Nb3Sn conductor have been designed, built and tested. D19H is a two-layer dipole magnet with a Nb3Sn inner layer and a recycled NbTi outer layer. Coil-pairs are connected with two of the four Nb3Sn splices in a high field region, and compressed by a ring and collet system. The ramp-rate sensitivity and the splice resistances were pleasingly low; and the 4.4K training was rapid. At 1.8K, however, the unusually high frequency of outer-coil fast-motion events increased with current, effectively creating a training-ceiling at 90% of the expected outer-layer limit (10.2 T). A low end-load applied to a relatively fluffy outer layer is believed to have caused this training limit. The end-load was increased; but a retest was aborted after the magnet failed a precautionary hipot test.