Overall critical current density of Chevrel wires at high magnetic field

Wires of Pb/sub 1-x/Sn/sub x/Mo/sub 6/S/sub 8/ (PSMS) using the powder-in-tube process have been carefully drawn and the critical current density J/sub c/ has been measured on small coils wound with wires of 1.5 meter in length in magnetic fields up to 24 tesla. At 1.9 K, we achieved an overall critical current density J/sub co/, exceeding slightly 100 A/mm/sup 2/ at 20 tesla and 63 A/mm/sup 2/ at 24 tesla. Below 18 tesla, we always observed an abrupt occurrence of the resistive state, indicating that in this region J/sub c/ is limited by local defects, generally located at the ends of the coil. Nevertheless, at 15 tesla and 4.2 K, J/sub c/ reaches 550 A/mm/sup 2/. These very good results are the consequence of a better choice of the materials forming the wire and of a full control of the synthesis of the PSMS powder, The analysis of the field dependence of J/sub c/ shows that the grains are well connected, but that the critical field B/sub c2/ is still too low at 4.2 K (31 tesla instead of 50 tesla). An optimization of the annealing conditions is expected to considerably increase J/sub c/ at high magnetic fields.