SuperKEKB 加速器用高温超伝導六極磁石のクエンチ検出と保護 ―REBCO コイルを用いたクエンチ実験と数値解析―

抄録

We are developing a high-temperature superconducting (HTS) sextupole magnet for chromaticity correction of the electron and positron beams of the SuperKEKB accelerator. The HTS sextupole magnet consists of six two-layer rectangular REBa2Cu3Oy (REBCO) coils. Since quench protection is a critical issue for the HTS sextupole magnet, we have carried out a series of quench studies on the REBCO coil. At the same time, we have developed a numerical simulation code to perform quench protection designs for the HTS sextupole magnet. In this study, we performed experiments and numerical simulations on the quench characteristics of three epoxy-impregnated REBCO model coils, two double pancake and a two-layer rectangular REBCO coils. The two-layer rectangular coil is the same as the coil of the HTS sextupole magnet. The hotspot temperature was studied as a function of the transport current and quench detection threshold. As a result, we confirmed experimentally that the quench protection of the REBCO coil could be achieved by a conventional quench detection method using the balance voltage. The validity of the numerical simulation code was also confirmed by comparing it with the experiments. Using the relation of the hotspot temperature and quench detection threshold, we succeeded in limiting the maximum quench temperature of the HTS sextupole magnet below 150 K.