In order to improve the critical current characteristics of Cu sheathed MgB2 wires, a study was made of the C doping and coating effects on JC of wires prepared by using an in situ powder-in-tube method. The Mg and B powders were mixed with a certain amount of MgB2 powder in order to increase the core density of wires in the heat treated samples. Pellets of the mixed powders were inserted into Cu sheaths and made into wires by rotary swaging, 2-axial rolling and drawing under cold-working. The wires were finally heat-treated (600C, 2h) in an Ar atmosphere. The critical current of short samples of graphite 5at%-doped MgB2/Cu with a diameter of 1.0mm attained 548A (JC = 440kA/cm2) at 4.2K in self-field. The reaction of Mg with Cu decreased for graphite coated samples, compared with non-coated ones. High-performance MgB2/Cu wires were obtained by doping with diamond and graphite powder using the in situ powder-in-tube method. It was found that the graphite coating on the inside surface of a Cu sheath was effective for suppressing the reaction of Mg with the Cu sheath. Solenoid coils were also fabricated by using the wind and react method and heat-treated under the above conditions. The JC 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 temperatures.

Graphite Coating Effects on the Critical Current Characteristics of MgB2/Cu Wires Fabricated by an in situ PIT Method. S.Shimura, T.Machi, K.Nakao, N.Koshizuka, S.Tanaka, K.Mochizuki, N.Shibata, K.Ushio: Physica C, 2005, 426-431[2], 1254-60