Speaker
Description
We have manufactured the 1/2-scale demonstration no-insulation (NI) REBCO magnet system for ‘skeleton cyclotron’ with no iron core (air-core), called “Ultra Baby Skeleton Cyclotron (UBSC).” The USBC magnet consists of center coils, main coils and AVF coils generating the azimuthal varying field. The outermost size of magnet is approximately 70 cm, and the designed center magnetic field is 1.6 T at an operating current of 540 A, corresponding to 5 MeV of proton acceleration energy. All the NI REBCO coils (center, main, and AVF) are connected in series, and the operating temperature is 30 K cooled by a conduction cooling system. In this R&D project, we will investigate the quality of fields generated by the developed REBCO magnet system including the screening current-induced fields, but we have no plant to accelerate particles.
In a charging test, the operating current increased up to 250 A. The developed UBSC magnet suddenly quenched in a few tens after stopping the magnet charging. The current 250 A is much smaller than the critical current of over 700 A. We observed that a few main NI REBCO coils have damaged with losing superconductivity after quench. To investigate the cause of quench, we have simulated the current behaviors during charging. As the result, the large screening currents were observed on the top and bottom main REBCO coils. However, the Hoop stress is not so high to damage the main REBCO coils. Meanwhile, the unexpected heating on REBCO tapes is seen on the simulation result. We will keep investigating the thermal stability of the developed UBSC NI REBCO magnet.
