Modeling of ‘quench’ or the occurrence and propagation of dissipative zones in REBCO high temperature superconducting coils

Abstract

Thanks to their very high current carrying capabilities even under high magnetic field conditions and their outstanding mechanical properties, high temperature superconductors (HTSs) such as REBCO (rare-earth BaCuO) tapes are very attractive for high magnetic field applications. Depending on the magnet design goals and constraints, it can be advantageous in some cases to reduce the electrical margins of the conductor. Considering the uncertainty in locally evaluating the critical current, and the inhomogeneities of present-day REBCO tapes, there is a significant risk of the critical current being overstepped locally, thus triggering local damaging hotspots. Such an event does not have the sudden occurrence and/or fast spreading quality usually associated with the concept of 'quench' and should be simply seen as thermal runaway induced by dissipative zones (DZs). The development of numerical models to evaluate the occurrence and propagation of such zones inside windings is critical in the development of a HTS magnet fully using REBCO tape performance while guaranteeing safe operation conditions. In this work, we have developed a transient electro-thermal model adapted to pancake-based coils. It accounts for both the nonlinear electrical and thermal behavior of the material and considers the local inhomogeneities of the critical current I c along the tape. The electrical part is one-dimensional (1D) and computes the nonlinear dissipation in the conductor depending on the local operation conditions while the thermal part is two-dimensional (2D) to account for the heat propagation along the conductor length and from turn to turn. In order to improve computation efficiency, adaptive time-stepping methods have been introduced with the objective of ensuring good accuracy of simulation results.

REBCO Coil With Robust Behavior Against Local Defects Wound Using Two-Tape Bundle

“…The discharge was completed sufficiently early that no damage occurred. In previous works, we introduced a thermal runaway model taking into account local Ic distribution [9] and applied it to the case of coils with localized defects for protection design purpose [10]. This model was used to reproduce the thermal runaway behavior in the experiment at 50 K (Fig.…”

Simulation of Local Dissipation Phenomena in the REBCO Insert of the 25-T CSM Magnet: Understanding and Preventing Destructive Thermal Runaway

“…The electric model is contained in external functions that are called for each blocks before each time step to evaluate the local heat generation. We will introduce briefly here the model hypothesis approach, the modelling implementation is presented in more details in [9].…”

“…This way were able to circumvent the limitations of the implementation of our model in Comsol that does not allow easily the coupling of electrical circuits. We are currently developping a more flexible implementation of the model [9] that includes such coupling, but for now it cannot manage a geometry with the dimensions considered here.…”

Current redistribution during inhomogeneous quench of 2G HTS tapes

“…This makes them prone to localized thermal runaways, which may lead to high temperature elevations, also called hot spots. This phenomenon is observed in many applications, such as resistive-type superconducting fault current limiters [1][2][3][4] or superconducting magnets [5]. The hot spot generally refers to a unique dissipative zone in the tape but an inhomogeneous heat dissipation with multiple dissipative zones preceding the complete quench of a tape is generally observed [6,7].…”