Reduction of toroidal magnetic field ripple with ferritic steel armors in JT-60U

Sakurai, Shinji; Masaki, Kei; Shibama, Yusuke; Shinohara, Koji; Suzuki, Yutaka; Sasajima, Tadayuki; Morioka, Atsuhiko; Hayashi, Takao; Takahashi, Ryukichi; Sawai, Tomotsugu; Fujita, Takaaki; Koide, Yoshihiko; Miura, Yukitoshi; Miya, Naoyuki; Kurihara, Kenichi

In order to reduce Toroidal magnetic Field (TF) ripple in JT-60U, ferritic steel (8Cr-2W-0.2V) armors were installed inside Vacuum Vessel (VV). 55 plates of 8Cr-2W-0.2V were manufactured from 2.6 ton ingots made by 20 ton vacuum induction melting. Saturated magnetization and thermal conductivity are 10-20% lower than those of F82H. Electrical resistivity and tensile properties are similar to those of F82H. 1122 carbon armors were replaced to 8Cr-2W-0.2V with reinforcement of stud nut. The absorbed beam power will be expected to increase 30%. A correction method of additional magnetic flux and field caused by 8Cr-2W-0.2V armors for magnetic probes is proposed for plasma position and shape control. Correction for flux loops is mostly good, but correcting model and program for B probe need some improvements.