Graphite coating effects on the critical current characteristics of MgB2/Cu wires fabricated by an in situ PIT method

Abstract

In order to improve the critical current characteristics of Cu sheathed MgB2 wires, we studied the carbon doping and coating effects on JC of wires prepared by an in situ powder-in-tube (PIT) method. Raw materials of Mg and B powders were mixed with a certain amount of MgB2 powder to increase the core density of wires in the heat treated samples. The pellets of these mixed powders were inserted into Cu sheaths and manufactured into wires by rotary swaging, two-axial rolling and drawing under cold-working. The wires were finally heat treated at 600°C for 2h in Ar gas atmosphere. The critical current IC of short samples of graphite 5at.% doped MgB2/Cu with diameter of 1.0mm reached 548A (JC=440kA/cm2) at 4.2K in self-field. The reaction of Mg with Cu decreased for graphite coating samples compared with non-coating ones. We obtained high performance MgB2/Cu wires by doping of diamond and graphite powder in the in situ PIT method. We found that the graphite coating on the inside surface of Cu sheath was effective for suppressing the reaction of Mg with Cu sheath. We also fabricated solenoid coils by wind and react method heat treated under the above conditions. The IC value was 230A at 4.2K for a coil produced by using a 16m wire. This coil generated a magnetic field of 0.42T at liquid He temperature.