Short Racetrack Windings for the Mechanical Characterization of Ceramic-Insulated Cables

Electrical insulation is a key element in high field magnets design. The use of Nb₃Sn, winded before reaction and then thermally treated to obtain the superconducting intermetallic compound, supposes to adapt the insulation process. CEA/IRFU (FR) is investigating the possibility of using a ceramic electrical insulation that follows the same thermal cycle than the superconductor. This ceramic insulation would make it possible to get rid of the impregnation process. The mechanical characterization of the ceramic-insulated cables is mandatory for the magnet designers. The increase of the Lorentz forces supposes to raise subsequently the characterization pressures, within the limits of the available press. An option to reach higher pressures with the same press is to reduce the sample surface by reducing its length. But approaching the twist pitch value, this can cause parasite effects such as sample untwisting, insulation cracks and boundary effect influence raise. Those effects appear to be particularly damaging in the case of ceramic insulation which is brittle. To address these problems, the use of short racetrack windings is proposed for characterization. The behavior of dummy copper cable with this ceramic insulation is studied till up to 150 MPa with such samples, at room temperature, in the stack direction.