Numerical investigation of current distributions around defects in high temperature superconducting CORC ® cables

The finite element method (FEM) provides a powerful support for the calculations of superconducting electromagnetic responses. It enables the analysis of large-scale high-temperature superconducting (HTS) systems by the popular H formulation. Nonetheless, modeling of contact resistivity in three-dimensional (3D) FEM is still a matter of interest. The difficulty stems from the large aspect ratio of the contact layer in numerical modeling. Nowadays, an available solution is to model the contact layer with zero thickness but requires the discontinuity conditions of the magnetic field. In this paper, the energy variational method is utilized to incorporate the contribution of contact resistivity into the H formulation. From the perspective of energy transfer, the contact resistivity is related to the energy dissipation of the radial current flowing through the contact interface. In terms of applications, this method can be employed to calculate the charging delay of no-insulation (NI) coils and the current sharing behaviors of CORC cables. One advantage of this model is that the magnetic field is continuous and hence can be easily implemented in FEM. Additionally, it requires fewer degrees of freedom and hence presents advantages in computational efficiency. Moreover, this method can be employed to simplify the 3D H homogeneous model for insulated coils. The above discussions demonstrate that the proposed model is a promising tool for the modeling of contact resistivity.

Section: Current Sharing Behaviors Of Corc Cablesupporting

confidence: 91%

Modeling of contact resistivity and simplification of 3D homogenization strategy for the H formulation

Wang,

Yong,

Zhou

2024

“…Simple electric-circuit models are a powerful tool to explain the measured V(I) behavior of rebco tapes and cables [59][60][61][81][82][83]. Here we use an approximate method, based on a dc electric-circuit model (figure C2), to interpret and gain insight on the performance of both wires in Layer 1 (table 4).…”

Section: Data Availability Statementmentioning

confidence: 99%

An initial magnet experiment using high-temperature superconducting STAR® wires

Wang

Bogdanof

Ferracin

et al. 2022

Self Cite

A dipole magnet generating 20 T and beyond will require high-temperature superconductors such as Bi2Sr2CaCu2O8-x and REBa2Cu3O7-x (RE = rare earth, REBCO). Symmetric tape round (STAR®) wires based on REBCO tapes are emerging as a potential conductor for such a magnet, demonstrating a whole-conductor current density of 580 A mm-2 at 20 T, 4.2 K, and at a bend radius of 15 mm. There are, however, few magnet developments using STAR® wires. Here we report a subscale canted cosθ dipole magnet as an initial experiment for two purposes: to evaluate the conductor performance in a magnet conﬁguration and to start developing the magnet technology, leveraging the small bend radius aﬀorded by STAR® wires. The magnet was wound with two STAR® wires, electrically in parallel and without transposition. We tested the magnet at 77 and 4.2 K. The magnet reached a peak current of 8.9 kA, 78% of the short-sample prediction at 4.2 K, and a whole-conductor current density of 1500 A mm-2. The experiment demonstrated a minimum viable concept for dipole magnet applications using STAR® wires. The results also allowed us to identify further development needs for STAR® conductors and associated magnet technology to enable high-ﬁeld REBCO magnets.

“…To investigate the problem of current sharing in an HTS cable, we implemented a 2D network model that calculates current and voltage distribution for a stack of ten HTS tape conductors current-shared through normal bulk metal in-between those conductors and having resistive current terminals interfaced to each of the conductors. Various public-domain and in-house developed circuit model realizations have been reported recently to provide current and voltage distributions for various HTS-related problems, such as a single HTS tape [24], HTS transformer [25], soldered stacked-twisted HTS wire [26], non-insulated coils [7,27] and CORC ® HTS cables [28]. Our model was implemented and solved using a freely available LTSpice ® circuit simulator by Linear Technologies [29].…”

Section: Current Sharing In a Tape Stackmentioning

confidence: 99%

Quench protection for high-temperature superconductor cables using active control of current distribution

Marchevsky,

Prestemon

2024

Self Cite

Superconducting magnets of future fusion reactors are expected to rely on composite high-temperature superconductor (HTS) cable conductors. In presently used HTS cables, current sharing between components is limited due to poorly defined contact resistances between superconducting tapes or by design. The interplay between contact and termination resistances is the defining factor for power dissipation in these cables and ultimately defines their safe operational margins. However, the current distribution between components along the composite conductor and inside its terminations is a priori unknown, and presently, no means are available to actively tune current flow distribution in real-time to improve margins of quench protection. Also, the lack of ability to electrically probe individual components makes it impossible to identify conductor damage locations within the cable. In this work, we address both problems by introducing active current control of current distribution between components using cryogenically operated metal-oxide-semiconductor-field-effect transistors (MOSFETs). We demonstrate through simulation and experiments how real-time current controls can help to drastically reduce heat dissipation in a developing hot spot in a two-conductor model system and help identify critical current degradation of individual cable components. Prospects of other potential uses of MOSFET devices for improved voltage detection, AC loss-driven active quench protection, and remnant magnetization reduction in HTS magnets are also discussed.