Experimental Measurement and Numerical Simulation of the Screening Current-Induced Field Decay in a Small ReBCO Coil

Self Cite

Different means are investigated today to protect a REBCO coil against local thermal runaway, what is commonly called a "Quench". Metal Insulated Coil or No-Insulated coil have been successfully introduced. However, these protections method may show other issues and are limited in terms of dynamics, making them impractical for fast applications. We successfully tested early detection of dissipative voltage followed by current dumping as a method to protect REBCO insulated test coils, even with engineering current density in the kA/mm2 range. Pick up coils can be used to compensate inductive coil voltage. In previous works we highlighted the presence of transient voltage due to the hysteretic current distribution in REBCO tape width, which can complicate the detection. We then developed a numerical electromagnetic model that reproduce the transient behaviour of REBCO coils. Here we study a small REBCO coil instrumented with three different pick-up coils, including a co-wound pick-up whose coupling is close to perfect. The post processing and analysis of the simulation results makes it possible to identify in the transient coil voltage the contribution due to transient losses and coil inductance variation. The resulting evaluation of the REBCO coil inductance and its variations is validated by analysis of the pick-up coil signals. From a practical point of view, this work shows the possibility to have very sensitive early detection of thermal runaway if the threshold is adjusted based on the expected coil compensated voltage drift. The interest of using isolated high-strength co-wound reinforcement tape as pick-up coil is also highlighted.

Section: Field Hysteresissupporting

confidence: 78%

Transient voltages and energy balance in REBCO insulated magnet: experimental and numerical studies

Vialle

Badel

Rozier

et al. 2021

Self Cite

“…The central magnetic induction measured is lower than the calculated one, with a value of 27.3 T. This is due to the screening current effect which lowers the field and degrades its homogeneity [14]. During this test campaign, we tried to reduce the screening currents by applying different loading sequences.…”

Section: Background Field Test Configurationmentioning

confidence: 92%

Metal-as-insulation sub-scale prototype tests under a high background magnetic field

Fazilleau¹,

Borgnic²,

Chaud³

et al. 2018

Self Cite

The aim of the NOUGAT project is to design and realize a 10 T high temperature superconducting solenoidal insert able to operate in a 20 T background magnetic induction. Our design is based on the metal-as-insulation winding technique consisting of co-winding a bare REBCO high temperature superconducting tape with a stainless steel tape. The metal-asinsulation winding maintains the self-protection feature of the no insulation winding and helps to reduce current charging time constants-one of the major drawbacks of no insulation coils-by significantly increasing the turn-to-turn electrical resistance. First, we demonstrated the selfquench protective behavior at 4.2 K under a high field up to 17 T by testing a single-pancake prototype. Then, before fabricating the final insert, we designed, wound and tested a second prototype made of two double-pancakes. The purposes were three-fold: validating the winding and assembly process, confirming the operating margins and corroborating the mechanical study. In this article, we present the main results of the tests performed at 4.2 K on this sub-scale prototype in a high background magnetic field at

“…Rare earth-barium-copper-oxide (REBCO) coated conductor (CC) has been regarded as a promising conductor option for ultrahigh magnetic field superconducting magnets. Meanwhile, the screening current (SC) induced in the REBCO CCs generates an undesired magnetic field [12,13,14,15]. Recently, it was pointed out that the screening current may substantially enhance magnetic stress in REBCO magnets [16,17,18,19,20,21].…”

Section: Introductionmentioning

confidence: 99%

A newly developed screening current simulation method for REBCO pancake coils based on extension of PEEC model

Noguchi¹,

Hahn²

2022

Since the screening current (SC) in rare earth-barium-copper-oxide (REBCO) coated conductor (CC) generates an undesired magnetic ﬁeld, it must be accurately estimated, especially for magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR). Moreover, in recent years, it was pointed out that the screening current enhanced the stress/strain in REBCO CC, when an REBCO magnet was operated as an insert under an ultrahigh magnetic ﬁeld. The previously reported SC simulation methods may be roughly categorized into ﬁnite element method (FEM) and equivalent circuit method. The FEM-based method often adopted an axisymmetric model or a thin ﬁlm approximation model, while the circuit-based are the simple equivalent circuit model and the network equivalent circuit model, so-called the partial element equivalent circuit model. The latter is newly proposed in this paper. Features of those SC simulation models are brieﬂy compared to each other in this paper. Each SC simulation models have pros & cons. We have to adequately chose an SC simulation model depending on a purpose. In addition, we propose a new developed SC simulation model, named the advanced partial element equivalent circuit (A-PEEC) model. It is extendable to an SC simulation of no-insulation REBCO pancake coils. To simulate the SC of a simple coil model and the LBC3 magnet, we investigated the screening current distribution maps, and the simulated screening current-induced ﬁelds were compared with the measurements. We have conﬁrmed the validity of the newly proposed A-PEEC model.