The fusion power density produced in a tokamak is proportional to its magnetic field strength to the fourth power. Second-generation high temperature superconductor (2G HTS) wires demonstrate remarkable engineering current density (averaged over the full wire), JE, at very high magnetic fields, driving progress in fusion and other applications. The key challenge for HTS wires has been to offer an acceptable combination of high and consistent superconducting performance in high magnetic fields, high volume supply, and low price. Here we report a very high and reproducible JE in practical HTS wires based on a simple YBa2Cu3O7 (YBCO) superconductor formulation with Y2O3 nanoparticles, which have been delivered in just nine months to a commercial fusion customer in the largest-volume order the HTS industry has seen to date. We demonstrate a novel YBCO superconductor formulation without the c-axis correlated nano-columnar defects that are widely believed to be prerequisite for high in-field performance. The simplicity of this new formulation allows robust and scalable manufacturing, providing, for the first time, large volumes of consistently high performance wire, and the economies of scale necessary to lower HTS wire prices to a level acceptable for fusion and ultimately for the widespread commercial adoption of HTS.

Structural engineering of topological bulk materials is systematically explored with regard to the incorporation of the buckled bismuth layer [Bi 2 ], which is a 2D topological insulator per se, into the layered BiTeI host structure. The previously known bismuth telluride iodides, BiTeI and Bi 2 TeI, offer physical properties relevant for spintronics. Herewith a new cousin, Bi 3 TeI (sp.gr. R3m, a = 440.12(2) pm, c = 3223.1(2) pm), joins the ranks and expands this structural family. Bi 3 TeI = [Bi 2 ][BiTeI] represents a stack with strictly alternating building blocks. Conditions for reproducible synthesis and crystal-growth of Bi 2 TeI and Bi 3 TeI are ascertained, thus yielding platelet-like crystals on the millimeter size scale and enabling direct measurements. The crystal structures of Bi 2 TeI and Bi 3 TeI are examined by X-ray diffraction and electron microscopy. DFT calculations predict metallic properties of Bi 3 TeI and an unconventional surface state residing on various surface terminations. This state emerges as a result of complex hybridization of atomic states due to their strong intermixing. Our study does not support the existence of new stacking variants Bi x TeI with x > 3; instead, it indicates a possible homogeneity range of Bi 3 TeI. The series BiTeI−Bi 2 TeI−Bi 3 TeI illustrates the influence of structural modifications on topological properties.

This paper describes the standalone magnet cold testing of the high temperature superconducting magnet Feather-M2.1-2. This magnet was constructed within the European funded FP7-EUCARD2 collaboration to test Roebel type HTS cable, and is one of the first high temperature superconducting dipole magnets in the world. The magnet was operated in forced flow helium gas with temperatures ranging between 5 to 85 K. During the tests a magnetic dipole field of 3.1 T was reached inside the aperture at a current of 6.5 kA and a temperature of 5.7 K. These values are in agreement with the self-field critical current of the used SuperOx cable assembled with Sunam tapes (lowperformance batch), thereby confirming that no degradation occurred during winding, impregnation, assembly and cool-down of the magnet. The magnet was quenched many tens of times by ramping over the critical current and no degradation nor training was evident. During the tests the voltage over the coil was monitored in the micro-volt range. An inductive cancellation wire was used to remove the inductive component, thereby significantly reducing noise levels. Close to the quench current, drift was detected both in temperature and voltage over the coil. This drifting happens in a time scale of minutes and is a clear indication that the magnet has reached its limit. All quenches happened approximately at the same average electric field and thus none of the quenches occurred unexpectedly.

Reproducibility of superconducting properties and suitability for specific applications by means of customised finish are two important attributes required from commercial 2G HTS wire. This paper reviews the consistent performance of SuperOx production 2G HTS wire and describes two novel customisation options: surround polyimide varnish insulation and composite bulk materials assembled with 2G HTS wires soldered together.

Halogen substitution, i. e. bromine for iodine, in the series of topological Bi n TeI (n = 1, 2, 3) materials is conducted in order to explore an impact of anion exchange on the topological electronic structure. In the proof-of-concept study we demonstrate the applicability of the modular view on the crystal and electronic structures of the new Bi 2 TeBr and Bi 3 TeBr compounds. Along with the isostructural telluroiodides, they constitute a family of layered structures that are stacked from two basic building modules, [ ஶ ଶ Bi 2 ] and [ ஶ ଶ BiTeX] (X = I, Br). We present solid-state synthesis, thermochemical studies, crystal growth and crystal-structure elucidation of Bi 2 TeBr (sp.gr. R3 തm (no. 166), a = 433.04(2) pm, c = 5081.6(3) pm) and Bi 3 TeBr (sp.gr. R3m (no. 160), a = 437.68(3) pm, c = 3122.9(3) pm). First-principles calculations establish the topological nature of Bi 2 TeBr and Bi 3 TeBr. General aspects of chemical bonding appear to be similar for Bi n TeX (X = I, Br) with the same n, so that the alternation of the global gap size upon substitution is insignificant. The complex topological inversion proceeds between the states of two distinct modules, [ ஶ ଶ Bi 2 ] and [ ஶ ଶ BiTeBr]; thus, the title compounds can be seen as heterostructures built via a modular principle. Furthermore, highly disordered as well as incommensurately modulated ternary phase(s) are documented near the Bi 2 TeBr composition. Single-crystal X-ray diffraction experiments on BiTeBr and Bi 2 TeI resolve some discrepancies in the prior published work.