Development of MgB2 superconducting wire for the low activation superconducting magnet system operated around core D-T plasma

• Published in: Fusion engineering and design 2015-10, Vol.98-99, p.1076-1080
• Main Authors: Hishinuma, Yoshimitsu, Kikuchi, Akihiro, Shimada, Yusuke, Kashiwai, Taro, Hata, Satoshi, Yamada, Shuichi, Muroga, Takeo, Sagara, Akio
• Format: Article
• Language: English
• Subjects: 11B boron isotope; Cu addition; Excitation test; MgB2; Solenoid coil
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2015.05.005

•We succeeded to fabricate 100m long MgB2/Ta/Cu mono-core wire and small solenoid coil for “low activation superconducting system”.•From the results of the coil excitatrion test, we conclude that MgB2 wire is an attractive alternative to NbTi for “low activation superconducting system”.•Jc property of the sample using 11B isotope powder was lower than those of the samples using natural and amorphous boron powder. We thought that fine particle sized 11B isotope powder is effective to improve Jc property of the sample made by 11B isotope. MgB2 is one of the “low activation superconductors”, because the half-life of the induced radio-activity on the MgB2 is much shorter than that of Nb-based superconductors such as NbTi, Nb3Sn and Nb3Al. MgB2 wire would become an alternative material for Nb-Ti wire for the Poloidal Field and correction feedback coils, if the critical current density (Jc) around the magnetic field of 4T could be improved. We found that addition of Cu using the compound Mg2Cu was an effective method to enhance Jc and succeed to fabricate 100m length of MgB2 wire with Cu addition. Jc of the 100m long MgB2 with Cu addition was comparable to that of a NbTi wire, and the small solenoid coil using Cu added MgB2 wire reached a central magnetic field of 2.62T. We found that MgB2 wire is an alternative material to commercial NbTi wires under the hard neutron irradiation in a fusion reactor. Furthermore, we also fabricated a Cu added MgB2 wire using isotope pure boron-11 (11B) powder as the boron source to reduce the radioactivity. The critical temperature (Tc) of the MgB2 wire using 11B powder was found to be 37K, and Tc was found to be changed by different boron materials.