Grease impregnation effect in measurement of critical current for NbTi superconductors

We have studied a measuring method of a critical current (I_c) for NbTi superconducting wires having a Cu matrix and Cu/CuNi matrices. To prevent the wires from prematurely quenching before reaching their I_c, we tried grease impregnations to sample coils. When the NbTi/Cu wire was used for the coil, silicon grease impregnation was enough to fix the wire and to measure the I_c of the wire. In case that we used the NbTi/Cu/CuNi wire when measuring the I_c, restraint of wire motion by the silicon grease impregnation was insufficient and the sample coil easily quenched before reaching the I_c. Accordingly, the Apiezon® (type: M) grease was used for an impregnation material, and we found the Apiezon grease was effective in fixing the NbTi/Cu/CuNi wire.