Reduction of the Hot Spot Temperature in HTS Coils

Abstract

Abstract-A potential future Muon Collider requires high field solenoids (>30 T) for the final cooling stage; the Magnet Division at Brookhaven National Laboratory (BNL) is undertaking the task of demonstrating feasibility using High Temperature Superconductors (HTS). The aim is to construct an all HTS dual-coil system capable of delivering more than 20 T. Recently a new record for an all HTS solenoid has been established with a field of 15 T on-axis. In coil tests it was noticed that during a fast energy extraction the current in the solenoids decays faster in comparison to the expected exponential decay. This paper describes the effect and shows how it can be simulated using commercial finite element code. The faster current decay helps to lower the integral current density squared with time by about 10% and is therefore beneficial for quench protection.

The Influence of Metal Plates on Quench Protection of High Temperature Superconducting Pancake Coils

“…The measurements show that the coupled copper plate can significantly accelerate the discharging process of the HTS coil at its early stage, which matches well with the previous studies in [21]. However, the coupled brass plate shows less effect on the discharging process, although it also speeds up the discharging process to some extent.…”

“…The current in the metal plates is assumed to be uniformly distributed, so metal plates can be equivalent to secondary coils for electromagnetic coupling with the HTS coil. This method is introduced in detail in [21]. The magnetic field module is coupled to the circuit network module to calculate the eddy current induced in the metal plates, and the governing equation is:…”

“…This can accelerate not only the discharge of the coil, but also the coil heating process. This has been proposed and studied based on copper plates [20], [21]. However, a variety of metal materials, such as copper, brass, aluminum alloy, and stainless steel, are promising alternatives for this technique.…”

SPICE model of high-temperature superconducting tape: application to resistive fault-current limiter

“…These inevitably result in local conservation of the hot-spot at least for the characteristic time until a circuit breaker switches. Note that the hot-spot problem is also an issue for CC-based magnetic systems [8,9]. As long as we are unable to influence the primary source of the problem (inhomogeneity of I c ), let us at least study its effect on processes of primary interest in CC-based devices.…”