Study on the Sintering and Mg Composition Effect on MgB2 Superconducting Bulks and Wires Synthesized by Powder-in-Sealed-Tube Method

Numerous research efforts aimed at the MgB2 (Magnesium diboride) as a superconducting material due to its higher critical temperature than Nb-based superconductors such as NbTi, Nb3Sn. Nowadays MgB2 is becoming more popular as the candidate to be applied on medical devices and large-scale applications because of its full coherence lengths, improved critical current density and fields, and simple crystal structure. In this study, we fabricated the 4 mm MgB2 superconducting wires by mixing stoichiometric mole ratio of Mg: B with 1.0:2.0 and 1.1:2.0 through the Powder-In-Sealed-Tube (PIST) method to optimize high critical temperature (TC) than the conventional MgB2 bulk and wire. Furthermore, we decreased the diameter of 4 mm to 1.8 mm wire and analyze the effect of critical temperature. The specimens were sintered at a different temperature to investigate the sintering effect of MgB2 superconducting wire. The resistivity versus temperature relationship, surface morphology, and crystal phase was characterized using Cryogenic system, SEM (Scanning Electron Microscopy), and XRD (X-ray Diffractometer), respectively. We optimized the high Tc,onset for the bulk and 4 mm wire compared to other studies that are 42.1K and 40.3K respectively at 800°C sintered temperature. Finally, the results suggest that the stoichiometric ratio of MgB2 exhibited excellent feasibility to prepare conventional MgB2 superconducting wire.

A Comparative Analysis of Economics of PMSG and SCSG Floating Offshore Wind Farms

The biggest obstacle to using a permanent magnet synchronous generator (PMSG) for a floating offshore wind turbine (FOWT) is the weight. A superconducting synchronous generator (SCSG) can be an alternative to this problem. In this paper, first, the weight and volume of a 10 MW class PMSG and SCSG for a large floating offshore wind farm (FOWF) were compared. Reflecting this, the economic feasibility of a 200 MW class FOWF based on a semi-submersible platform was compared and analyzed. The levelized cost of energy (LCOE) was used to compare the economics of the two types of FOWF, and the LCOE of the SCSG type FOWF was 6 (USD/MWh) more expensive than that of the PMSG type FOWF. However, if the superconducting wire price is reduced by 40% compared to the current price, the economic feasibility of the SCSG type FOWF can be secured. Considering only the weight, the SCSG type FOWF is far superior to the PMSG type FOWF. With the trend of falling superconducting wire prices and improving critical current, the SCSG type FOWF is expected to become a definite alternative to large-capacity wind farms, and the economic feasibility is expected within the next five years.

New types of topological superconductors under local magnetic symmetries

We classify gapped topological superconducting (TSC) phases of one-dimensional quantum wires with local magnetic symmetries (LMSs), in which the time-reversal symmetry $\mathcal {T}$ is broken but its combinations with certain crystalline symmetry such as $M_x \mathcal {T}$, $C_{2z} \mathcal {T}$, $C_{4z}\mathcal {T}$, and $C_{6z}\mathcal {T}$ are preserved. Our results demonstrate that an equivalent BDI class TSC can be realized in the $M_x \mathcal {T}$ or $C_{2z} \mathcal {T}$ superconducting wire, which is characterized by a chiral Zc invariant. More interestingly, we also find two types of totally new TSC phases in the $C_{4z}\mathcal {T}$, and $C_{6z}\mathcal {T}$ superconducing wires, which are beyond the known AZ class, and are characterized by a helical Zh invariant and Zh⊕Zc invariants, respectively. In the Zh TSC phase, Z-pairs of MZMs are protected at each end. In the $C_{6z}\mathcal {T}$ case, the MZMs can be either chiral or helical, and even helical-chiral coexisting. The minimal models preserving $C_{4z}\mathcal {T}$ or $C_{6z}\mathcal {T}$ symmetry are presented to illustrate their novel TSC properties and MZMs.