Aiming at application to future fusion reactor magnets, the development of large-current capacity high-temperature superconducting (HTS) conductors has started around the world. The present status of various conductor concepts and their properties are introduced. Future prospects are also discussed.
The SuperKEKB electron-positron collider is an accelerator that has been upgraded for the KEKB. This collider is designed to explore New Physics beyond the Standard Model of particle physics in the B meson regime. The target of SuperKEKB is to attain a luminosity that is 40 times higher than that of the KEKB. To accomplish this, a new beam final focus system of the superconducting magnets was constructed based on the accelerator design of “nano beam scheme”. The system has the extremely significant function of squeezing beams to 0.05 μm from 1 μm in the KEKB, and the luminosity is expected to increase to a value 20 times higher through this process. SuperKEKB has completed Phase-2 beam operation, and the first beam collision was observed on April 26th, 2018. This paper describes the superconducting magnets and cryostat system for focusing beams at the interaction point.
We have developed a lumped element kinetic inductance detector (LEKID) process to suppress non-uniformity in a distribution of resonant frequencies. Non-uniformity of the frequency interval between neighboring resonant frequencies can be caused by the crosstalk among the resonators in the frequency domain. We find that the non-uniformity is attributed not only to electromagnetic coupling among the resonators, but also to the non-uniform depth of over-etching on the silicon substrate surface produced during the reactive ion etching of resonator electrodes. The former is mitigated by forming a ground shield around the resonators, and the latter can be removed by forming a thin AlN layer on the substrate that acts as an etch-stopper. With the improvements, we achieve a uniform distribution of resonant frequencies that meets our requirements.