Speaker
Description
The no-insulation (NI) technology is a powerful technique toward very high field generation over 40 T. The National High Magnetic Field Laboratory (NHMFL), in 2017, successfully generated a field of 45.5 T, which is the world record for the DC field [1]. The success is attributed to the use of rare-earth barium copper oxide (REBCO) and the NI technology. REBCO conductors can withstand a very high magnetic field and mechanical stress, while the NI technology grants the REBCO coil very high thermal stability. The combination of REBCO conductors and NI technology is promising and adopted in many high-field magnets [2], [3], [4]. One of the major drawbacks of the NI REBCO coils is the screening current effect. Screening currents are induced when a field perpendicular to the REBCO tape changes; i.e., during magnet energization and de-energization. The screening current causes the unbalanced current distribution in the REBCO conductors and consequent unbalanced forces, which may lead to excessive electromagnetic forces and possible conductor degradations in such a high field [5]. The temporal field instability due to the screening current is an undesired characteristic as well. Reducing or suppressing the screening currents can open the way for the higher field generation.
In this presentation, we propose the use of NI REBCO windings as shielding coils from the screening current fields. The NI REBCO windings, which are not energized, are placed close to the edge sides of the main NI REBCO coil, and the non-energized NI REBCO coil prevents the radial field change and reduces the screening current. The electromagnetic simulation is performed using the partial element equivalent circuit (PEEC), and the electromagnetic behaviors of the shielding coil, as well as the suitable configuration of the NI REBCO windings, are investigated.
