Thermal creep and -runaway in conduction-cooled, layer-wound ReBCO coils

Description

The spatial and temporal temperature distribution within the windings of insulated layer-wound ReBCO coils has been simulated and
measured under a range of excitation currents and cooling conditions, in order to investigate the boundary between transient thermal creep and an actual
quench precursor.
Many authors report an initially slow but gradually accelerating upward temperature creep in ReBCO coils after an upward current step, typically observed
as a gradually rising coil voltage. This well-known phenomenon can occur of the order of hours, or even days to weeks, for large, conduction-cooled systems
and is often difficult to detect. If left unchecked, it can lead to thermal runaway and catastrophic failure, necessitating active protection even for apparently
stable coils. Qualitatively, this behaviour can be satisfactorily described with a straightforward non-linear self-heating model, but it is difficult to accurately
predict the sharp boundary between stable and unstable excitation regimes. We extend on this type of “0D” models by incorporating a more detailed
temperature distribution throughout the winding pack.
In order to verify our simulation model, we developed and calibrated 50 micrometre-size thermocouple sensors that can be co-wound in ReBCO coils without
significantly altering the properties of the windings. These sensors achieve a temperature precision of a few millikelvin at about 77 K, allowing highly
localized in-situ temperature measurements. This level of detail surpasses conventional experimental methods. Several ReBCO coils with different insulation
parameters are tested using this technique, in both liquid nitrogen immersion and conduction-cooled environments, and the results are compared to 0D and
distributed model predictions.

Period	24 Sept 2025
Event title	17th European Conference on Applied Superconductivity, EUCAS 2025
Event type	Conference
Conference number	17
Location	Porto, PortugalShow on map
Degree of Recognition	International