Coils for rare-earth barium copper oxide (REBCO) high temperature superconductor (HTS) magnets are often wound with insulation between turns (i.e. effectively infinite resistance). In this case, magnetic field generated by the coil is linearly related to the transport current in the coil, allowing voltage-limited magnet ramping. However, quench protection has been shown to be hard to implement using either standard passive or active quench protection schemes.
Introducing a finite resistance between turns adds a new radial current path in addition to the desired azimuthal current path. Now current may automatically bypass quenched areas, avoiding irreversible damage. However, finite resistivity between turns means that there may no longer be a linear relationship between transport current and magnetic field. The lag between the transport current reaching its operating value and the coil field reaching its operating value we term the settling time. Setting the resistivity between turns allows control of the settling time, which in turn determines how readily current may bypass quenched areas in the event of quench.
We wish to manufacture a quench tolerant ReBCO MRI magnet, making use of epoxy encapsulated coils for strength, with finite resistivity between turns. However, it is well-known that any magnet for magnetic resonance applications requires excellent field stability and uniformity. Magnets with low turn-to-turn resistivity have been shown to have excessively long settling times which will yield a slowly changing magnetic field magnitude and uniformity unsuitable for MRI. We have therefore developed software to model and calculate the turn-to-turn resistivity