Masazumi Hirakawa

Effect of aromatic hydrocarbon addition on in situ powder-in-tube processed MgB2 tapes

We fabricated in situ powder-in-tube processed MgB2/Fe tapes using the aromatic hydrocarbons benzene, naphthalene, and thiophene as additives, and investigated the superconducting properties. We found that these aromatic hydrocarbons were very effective for increasing the Jc values. The Jc values of 20 mol% benzene-added tapes reached 130 A mm−2 at 4.2 K and 10 T. This value was almost comparable to that of 10 mol% SiC-added tapes and about four times higher than that of tapes with no additions. Microstructural analyses suggest that this Jc enhancement is due to both the substitution of carbon for boron in MgB2 and the smaller MgB2 grain size.

Critical current densities of powder-in-tube MgB2 tapes fabricated with nanometer-size Mg powder

We fabricated powder-in-tube MgB2/Fe tapes using a powder mixture of nanometer-size Mg and commercial amorphous B and investigated the transport properties. High-purity nanometer-size Mg powder was fabricated by applying the thermal plasma method. 5–10 mol % SiC powder doping was tried to enhance the Jc properties. We found that the use of nanometer-size Mg powder was effective to increase the Jc values. The transport Jc values of the nondoped and 10 mol % SiC-doped tapes prepared with nanometer-size Mg powder reached 90 and 250 A/mm2 at 4.2 K and 10 T, respectively. These values were about five times higher than those of the tapes prepared with commercial Mg powder.

Fabrication of A15-type superconducting tape conductors by applying the ex situ powder-in-tube method

It is well known that MgB2 tape conductors can be fabricated by the ex situ powder-in-tube (PIT) method with MgB2 powder and without any heat treatment. We fabricated different A15-type superconducting tapes by applying this ex situ PIT method. Nb3Sn, Nb3Al, or V3Si superconducting powder was tightly packed into a stainless steel (SUS316) tube or a Cu–10 wt% Ni tube. These tubes were cold rolled into tapes by using groove rolling and flat rolling. Rigid A15 superconducting cores were obtained after cold rolling. All the tapes showed substantial Jc values at 4.2 K without any heat treatment. The superior mechanical hardness of the sheath material was effective for obtaining a superconductor core of high density and realizing high Jc values. Jc increased with increasing degree of cold rolling. This Jc increase was also due to the increase in the density of the superconducting core. The highest Jc of at 6 T and 4.2 K was obtained for the Nb3Al/(SUS316) tape. This Jc value was much higher than that of the ex situ-processed MgB2/(SUS316) tapes. The temperature dependence of the Bc2 of the Nb3Sn/(SUS316) tape, d Bc2/d T, was almost equal to that of the bronze-processed Nb3Sn conductor. Annealing at after cold rolling considerably enhanced Jc values of all tapes.

Development of 2T‐Class MgB2 Solenoid Coil

This paper reports on the fabrication and testing of a MgB2 coil made using a wind & react method. We made a 130m‐long Fe/Cu‐composite sheathed, SiC‐doped MgB2‐superconducting round wire using an in‐situ PIT method. Using a 92m‐long wire, we fabricated a solenoid coil with 722 turns. In the coil test, we measured the Ic of the coil under various external fields and temperatures. The Ic of the coil reached 162 A (Je = 340 A/mm2) at 4.2 K and in the external field of 2 T. The coil generated 2.2 T (the center magnetic field, Bo); thus the total field reached 4.2 T. The Je exceeded 100 A/mm2 in the external fields of 4 T, 2.5 T, and 1 T at 15 K, 20 K, and 25 K, respectively. The Jc of the coil was almost equal to that of the short sample. This indicates that the 92m‐long wire has a very homogeneous Jc distribution.