Quench Study on a REBa₂Cu₃O_y Coil for a High Temperature Superconducting Sextupole Magnet

We are developing a high temperature superconducting (HTS) sextupole magnet for the chromaticity correction of the electron and positron beams of SuperKEKB accelerator. The HTS sextupole magnet consists of six two-layers rectangular REBa ₂ Cu ₃ O _y (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. As 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 a two-layers rectangular epoxy-impregnated REBCO coil that is the same size coil for the actual HTS sextupole magnet. The hotspot temperature was studied as a function of the transport current and quench detection threshold. As a result, we experimentally confirmed 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 was also confirmed by comparing with the experiments. Using the relation of the hotspot temperature and quench detection threshold, we could performed a protection design to limit the maximum quench temperature of the HTS sextupole magnet below 150 K.