Prospects of High Temperature Superconductors for fusion magnets and power applications

Analysing neutron radiation damage in YBa2 Cu3 O7-x high temperature superconductor tapes

Superconducting windings will be necessary in future fusion reactors to generate the strong magnetic fields needed to confine the plasma, and these superconducting materials will inevitably be exposed to neutron damage. It is known that this exposure results in the creation of isolated damage cascades, but the presence of these defects alone is not sufficient to explain the degradation of macroscopic superconducting properties and a quantitative method is needed to assess the subtle lattice damage in between the clusters. We have studied REBCO coated conductors irradiated with neutrons to a cumulative dose of 3.3×10²²  n*m^-2  that show a degradation of both T_c  and J_c values, and use HRTEM analysis to show that this irradiation introduces ∼10 nm amorphous collision cascades. In addition we introduce a new method for the analysis of these images to quantify the degree of lattice disorder in the apparently perfect matrix between these cascades. This method utilises Fast Fourier and Discrete Cosine Transformations of a statistically-relevant number of HRTEM images of pristine, neutron-irradiated, and amorphous samples, and extracts the degree of randomness in terms of entropy values. Our results show that these entropy values in both mid-frequency band FFT and DCT domains correlate with the expected level of lattice damage, with the pristine samples having the lowest and the fully amorphous regions the highest entropy values.  Our methodology allows us to quantify 'invisible' lattice damage to and correlate these values to the degradation of superconducting properties, and also has relevance for a wider range of applications in the field of electron microscopy where small changes in lattice perfection need to be measured. This article is protected by copyright. All rights reserved.

Over 15 MA/cm2 of critical current density in 4.8 µm thick, Zr-doped (Gd,Y)Ba2Cu3Ox superconductor at 30 K, 3T

An Advanced MOCVD (A-MOCVD) reactor was used to deposit 4.8 µm thick (Gd,Y)BaCuO tapes with 15 mol% Zr addition in a single pass. A record-high critical current density (J_c) of 15.11 MA/cm² has been measured over a bridge at 30 K, 3T, corresponding to an equivalent (I_c) value of 8705 A/12 mm width. This corresponds to a lift factor in critical current of ~11 which is the highest ever reported to the best of author’s knowledge. The measured critical current densities at 3T (B||c) and 30, 40 and 50 K, respectively, are 15.11, 9.70 and 6.26 MA/cm², corresponding to equivalent Ic values of 8705, 5586 and 3606 A/12 mm and engineering current densities (J_e) of 7068, 4535 and 2928 A/mm². The engineering current density (J_e) at 40 K, 3T is 7 times higher than that of the commercial HTS tapes available with 7.5 mol% Zr addition. Such record-high performance in thick films (>1 µm) is a clear demonstration that growing thick REBCO films with high critical current density (J_c) is possible, contrary to the usual findings of strong J_c degradation with film thickness. This achievement was possible due to a combination of strong temperature control and uniform laminar flow achieved in the A-MOCVD system, coupled with optimization of BaZrO₃ nanorod growth parameters.

No-insulation multi-width winding technique for high temperature superconducting magnet

We present a No-Insulation (NI) Multi-Width (MW) winding technique for an HTS (high temperature superconductor) magnet consisting of double-pancake (DP) coils. The NI enables an HTS magnet self-protecting and the MW minimizes the detrimental anisotropy in current-carrying capacity of HTS tape by assigning tapes of multiple widths to DP coils within a stack, widest tape to the top and bottom sections and the narrowest in the midplane section. This paper presents fabrication and test results of an NI-MW HTS magnet and demonstrates the unique features of the NI-MW technique: self-protecting and enhanced field performance, unattainable with the conventional technique.