arXiv subjects

Doan N. Nguyen

Publications and source records attributed to Doan N. Nguyen.

3 recordsLinked to original sources

arXiv2023

Sudden adiabaticity entering field-induced state in UTe2

There has been a recent surge of interest in UTe$_2$ due to its unconventional magnetic field (H) reinforced spin-triplet superconducting phases persisting at fields far above the simple Pauli limit for H $\parallel$ [010]. Magnetic fields in excess of 35 T then induce a field-polarized magnetic state via a first-order-like phase transition. More controversially, for field orientations close to H $\parallel$ [011] and above 40 T, electrical resistivity measurements suggest that a further superconducting state may exist. However, no Meissner effect or thermodynamic evidence exists to date for this phase making it difficult to exclude a simple low-resistance metallic state. In this paper, we describe a study using thermal, electrical, and magnetic probes in magnetic fields of up to 55 T applied between the [010] ($b$) and [001] ($c$) directions. Our MHz conductivity data reveal the field-induced state of low or vanishing electrical resistance; simultaneous magnetocaloric effect measurements (i.e. changes in sample temperature due to changing magnetic field), show the first definitive evidence for adiabaticity and thermal behavior characteristic of bulk field-induced superconductivity.

cond-mat.supr-con↗

arXiv2023

Understanding and minimizing ac losses in CORC cables of YBCO superconducting tapes

AC losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different AC loss components and provide approaches for reducing AC losses in cables. An FEA model based on T-A formula treats the cross-section of thin superconducting layers as 1D lines and, therefore, only can predict the AC loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross-section HTS tapes to provide the total AC losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. Both 1D and 2D simulation approaches were employed to offer a comprehensive understanding of the effects of cable design and operational parameters on the AC loss components in a 2-layer CORC cable. The research results given in this paper are therefore not only valuable to suggest strategies for reducing AC loss in multi-layer cables but also for developing more accurate and effective methods to calculate AC loss in CORC HTS cables.

cond-mat.supr-con↗

arXiv2013

Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents

Numerical modeling of superconductors is widely recognized as a powerful tool for interpreting experimental results, understanding physical mechanisms and predicting the performance of high-temperature superconductor (HTS) tapes, wires and devices. This is especially true for ac loss calculation, since a sufficiently low ac loss value is imperative to make these materials attractive for commercialization. In recent years, a large variety of numerical models, based on different techniques and implementations, have been proposed by researchers around the world, with the purpose of being able to estimate ac losses in HTSs quickly and accurately. This article presents a literature review of the methods for computing ac losses in HTS tapes, wires and devices. Technical superconductors have a relatively complex geometry (filaments, which might be twisted or transposed, or layers) and consist of different materials. As a result, different loss contributions exist. In this paper, we describe the ways of computing such loss contributions, which include hysteresis losses, eddy current losses, coupling losses, and losses in ferromagnetic materials. We also provide an estimation of the losses occurring in a variety of power applications.

cond-mat.supr-con↗