Transient voltages observed over a large-scale prototype of a cryogen-free HTS insert coil
ZAMPA Alexandre, 高橋 弘紀 （東北大）； BADEL Arnaud （University Grenoble Alpes）； 土屋 雄司, 岡田 達典, 淡路 智 （東北大）； 宇都 達郎, 武輪 裕之, 花井 哲, 井岡 茂, 稲垣 淳二 （東芝エネルギーシステムズ）
Abstract:The High Field Laboratory for Superconducting Materials (Tohoku University) and Toshiba® are currently developing a 19T insulated HTS coil for its future 33T cryogen-free superconducting magnet. The architecture of the coil is based on the robust concept aiming to cope with the occurrence of local degradation in the HTS tape and to withstand high mechanical stresses. One large-scale prototype of this HTS insert, consisting of 20 stacked pancakes, was manufactured, and successfully tested in liquid Helium inside a 14 T LTS magnet, reaching a total magnetic field of 25 T and validating the coil mechanical design.
The HTS coil protection sequence is based on the early detection of dissipation followed by a rapid discharge in a dump resistor. The existence of dissipation in the coil is reflected by a sudden change of slope in the coil’s voltage. This new contribution must be detected while it is small enough not to turn to thermal runaway. To make this recognition easier, the bulk of the inductive contribution is removed from the coil’s total voltage, leaving the contributions of the losses and the possible dissipation.
Another phenomenon, already detailed in the literature, occurring when the current penetrates virgin zones of the tapes, implies a transient voltage showing a dissipation-like voltage. A good understanding of this phenomenon is important to efficiently protect the HTS coil and not to hinder the recognition of the transient voltage of interest coming from dissipation. This contribution aims to present these transient voltages rarely observed in such large-scale HTS coil. To do so, first, the protection sequence will be detailed. Then, observation of dissipative contribution in the detection voltage will be introduced as well as the transient voltage coming from the magnetization of virgin zones of the HTS tapes.