Observations from the Analyses of Magnetic Field and AC Loss Distributions in the NHMFL 32 T All-Superconducting Magnet HTS Insert

Abstract

A 17 T high-temperature superconducting two-coil magnet (insert) to be operated in a 15 T low-temperature superconducting multisection magnet (outsert) is the most demanding part of the National High Magnetic Field Laboratory all-superconducting 32 T magnet system. The HTS coils are of the pancake type and to be wound with REBCO coated conductors/tapes manufactured by SuperPower, Inc. The distribution of AC losses in the HTS windings during the magnet charging/discharging process are computed and analyzed with due regard for the AC loss density dependence on the magnetic field and the field angle. The calculations are based on the measured magnetization of a representative sample against magnetic field and field angle. The results enable determination of heat load on the magnet and its cryogenic system. Since the magnet is of the pool-cooled type, a related helium vapor bubble problem can develop owing to the high field and field gradients, and the diamagnetic susceptibility of helium.

Development of general expressions for the temperature and magnetic field dependence of the critical current density in coated conductors with variable properties

“…Knowledge of J c (B, θ) for each conductor at varying temperatures is required for accurate quench modeling, but the large number of conductors and their generally short lengths makes generation of J c (B, θ, T) for each conductor length an unrealistic and time-consuming task. To start to assess the true nature of this challenge, this paper was designed to explore J c (B, T) for 4 tapes across the significant range of properties obtained in the 32 T procurement for which an extensive quench model was developed [16][17][18], originally on the basis of extended measurements on just one tape [9].…”

Practical fit functions for transport critical current versus field magnitude and angle data from (RE)BCO coated conductors at fixed low temperatures and in high magnetic fields

“…Using these over previous models, the electromagnetic performance of coils wound with these conductors can be predicted more effectively. In particular, the nonlinear fit in section 8 of this article of transport critical current versus field and angle data at T = 4.2 K was used to estimate the hysteresis losses of (RE) BCO coated conductors in high magnetic fields, and to design the inserts wound with such conductors of the all-superconducting 32 T magnet being constructed at the NHMFL [1][2][3][4]. A series of such fits was developed at several fixed temperatures for use in simulating the quench behavior of that magnet.…”

Critical Current Simulation and Measurement of Second Generation, High-Temperature Superconducting Coil under External Magnetic Field

“…Second generation (2G), high-temperature superconductors (HTS), also known as Rare Earth Barium Copper Oxide (REBCO) tapes, have high critical currents under external magnetic fields; thus, pancake coils wound with REBCO are widely used as insert magnets for high magnetic field devices [ 1 , 2 , 3 , 4 , 5 ]. As such, attentions have been devoted to investigating the properties of these coils [ 6 , 7 , 8 ]. For high-field applications, the critical current of REBCO coils is one of the key issues.…”