Repetitive excitation and demagnetization for magnetic refrigeration using static superconducting coils with trapezoidal wave current generated by resonance and switch operation

Abstract

Hydrogen has emerged as a promising alternative to fossil fuels due to its key advantage of producing no carbon dioxide during consumption. Liquefaction of hydrogen is recognized as a preferable method for storing substantial quantities. Achieving efficient cooling technology is particularly crucial in the temperature range near 20 K, which aligns with the boiling point of hydrogen. Magnetic refrigeration represents a viable approach to this achievement. Repetitive changes in the magnetic field in magnetocaloric materials are required for magnetic refrigeration and can be obtained using static superconducting coils with trapezoidal wave current.

To efficiently reduce electric power consumption, it was conceived that the trapezoidal wave current could be generated approximately through resonance as alternating current if static superconducting coils were combined with capacitors charged by a power supply. However, the alternating current will inevitably attenuate over time due to circuit resistance.

This study reports a method for modifying the alternating current into the trapezoidal wave current and recovering it to the initial value against attenuation. The method will be beneficial if the residual ratio against the attenuation is accepted to a certain amount. This method consists of a circuit incorporating three switches into a combination of a static superconducting coil and a capacitor with a power supply. By toggling these switches when the alternating current due to resonance reaches its maximum or zero, the alternating current is converted into a trapezoidal wave current and restored to its initial value against attenuation.

A practical case of the method was simulated using analytic software “LTspice.” A small-scale case of the method was experimented and subsidiarily simulated using a palm-sized REBCO coil in liquid nitrogen and an electric double-layer capacitor in the atmosphere. Consequently, the trapezoidal wave current by the resonance method was fundamentally confirmed.