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Jiang, Jianyi

Publications and source records attributed to Jiang, Jianyi.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

ac susceptibility studies of intra- and intergrain properties of high-$J_c$ Bi-2212 wires

Bi 2 Sr 2 CaCu 2 O x (Bi-2212) is the only high-$T_c$ superconductor (HTS) available as a multifilamentary round wire with multiple architectures and it is a very promising conductor for the realization of high-field applications. Despite their relatively simple wire fabrication by the powder-in-tube technique, Bi-2212 wires require a tightly controlled overpressure heat treatment (HT) with a multi-parameter time-temperature schedule to achieve high critical current density, $J_c$. Further, the variation of these HT parameters, changes in the wire design, wire diameter and powder quality can lead to variations in both the microstructure and the superconducting performance. Particularly noticeable are variations in $J_c$ performance and degree of filament bridging. In this work, we focus on the use of different magnetic characterization techniques to estimate the bridging level and assess the balance of INTER-grain and intra-grain superconducting properties including the irreversibility field ($H_{\text{irr}}$) and the pinning energy ($U_0$) in differently processed wires. Regardless of the actual bridging level, we find that the supercurrent flows at the filament bundle level, not just at the individual filament level. Moreover, using AC susceptibility we identify two distinct supercurrent contributions, one related to the intra-grain and one to the INTER-grain properties, whose irreversibility fields are different but without large sample-to-sample variation. Moreover, an additional component of intra-grain pinning mechanism becomes effective at low temperatures with positive effects also on the INTER-grain performance. The work clearly shows that detailed magnetic characterizations can become valuable tools to investigate the performance of differently processed Bi-2212 wires, correlating their microstructure and overall transport $J_c$, to obtain a deeper understanding of the causes of performance variation and paths to achieve further improvement.

2212↗
DOE OSTI2021

Effects of Wire Diameter and Filament Size on the Processing Window of Bi-2212 Round Wire

High engineering critical current density (J E of 1300 A/mm 2 at 4.2 K and 15 T) in Bi-2212 round wire has been achieved through a partial melt, overpressure heat treatment process. J E varies strongly with processing conditions, particularly the maximum heat treatment temperature (T max ). Increasing T max results in longer time in the melt (defined as the time between when Bi-2212 melts on heating and when Bi-2212 begins to form on cooling), more bridging between the filaments, lower J E , and higher ac losses. A wide processing window with a large range of T max that has a nearly constant J E is desired for processing large coils with large thermal mass and significant thermal time constants that may make precise control over the desired temperature – time profiles uncertain. Accordingly, we wanted to explore broadening the T max window by controlling the Bi-2212 powder melting or wire architecture design. In this work, we report on studies of the performance variation with T max for two production wires with a filling factor of about 20% and 85 × 18 filaments where filament size was varied by changing the wire diameter, a process which also shortens the distance between filaments. We found that wires with smaller filament diameter (9 to 11 μm) showed a peak J E at the low end of T max and also a J E that was more sensitive to T max . A J E – T max plot showed a plateau J E (4.2 K, 5 T) of ~1100 A/mm 2 between T max of 886 and 894 °C for 1.0 and 1.2 mm wires, where J E is less sensitive to the wire diameter and T max . This J E plateau range is a preferred processing window for achieving high J E in coils.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Critical Current Distributions of Recent Bi-2212 Round Wires

Bi 2 Sr 2 CaCu 2 O 8+x (Bi-2212) is the only high-field, high-temperature superconductor (HTS) capable of reaching a critical current density J c (16 T, 4.2 K) of 6500 A·mm –2 in the highly desirable round wire (RW) form. However, state-of-the-art Bi-2212 conductors still have a critical current density (J c ) to depairing current density (J d ) ratio around 20 to 30 times lower than that of state-of-the-art Nb–Ti or REBCO. Previously, we have shown that recent improvements in Bi-2212 RW J c are due to improved connectivity associated with optimization of the heat treatment process, and most recently due to a transition to a finer and more uniform powder manufactured by Engi-Mat. One quantitative measure of connectivity may be the critical current (I c ) distribution, since the local I c in a wire can vary along the length due to variable vortex-microstructure interactions and to factors such as filament shape variations, grain-to-grain connectivity variations and blocking secondary phase distributions. Modeling the experimental V-I transition measured on a low resistance shunt as a complex sum of voltage contributions of individual filament and wire sub-sections allows a numerical extraction of the I c distribution from the d 2 V/dI 2 treatment of the V-I curves. Here we compare ~0.1 m length I c distributions of Bi-2212 RWs with recent state-of-the-art very high-J c Engi-Mat powder and lower J c and older Nexans granulate powder. We do find that the I c spread for Bi-2212 wires is about twice the relative standard of high-J c Nb–Ti well below H irr . We do not yet see any obvious contribution of the Bi-2212 anisotropy to the I c distribution and are rather encouraged that these Bi-2212 round wires show relative I c distributions not too far from high-J c Nb–Ti wires.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Densified superconductor materials and methods

Methods of pre-densifying a metal wire containing superconductor materials are provided. Superconductor materials containing the pre-densified wires also are provided. The wires may be pre-densified by subjecting a metal wire that includes one or more filament cavities in which a superconductor precursor powder is disposed to a temperature and a first pressure for a time sufficient to densify the superconductor precursor powder to form a pre-densified metal wire, wherein the temperature is less than the melting point of the superconductor precursor powder, and the first pressure is sufficient, at the temperature, to compress at least a portion of the metal wire.

Matras, Maxime R.↗
DOE OSTI2019

Stable, predictable and training-free operation of superconducting Bi-2212 Rutherford cable racetrack coils at the wire current density of 1000 A/mm 2

High-temperature superconductors (HTS) could enable high-field magnets stronger than is possible with Nb-Ti and Nb 3 Sn, but two challenges have so far been the low engineering critical current density J E , especially in high-current cables, and the danger of quenches. Most HTS magnets made so far have been made out of REBCO coated conductor. Here we demonstrate stable, reliable and training-quench-free performance of Bi-2212 racetrack coils wound with a Rutherford cable fabricated from wires made with a new precursor powder. These round multifilamentary wires exhibited a record J E up to 950 A/mm 2 at 30 T at 4.2 K. These coils carried up to 8.6 kA while generating 3.5 T at 4.2 K at a J E of 1020 A/mm 2 . Different from the unpredictable training performance of Nb-Ti and Nb 3 Sn magnets, these Bi-2212 magnets showed no training quenches and entered the flux flow state in a stable manner before thermal runaway and quench occurred. Also different from Nb-Ti, Nb 3 Sn, and REBCO magnets for which localized thermal runaways occur at unpredictable locations, the quenches of Bi-2212 magnets consistently occurred in the high field regions over a long conductor length. These characteristics make quench detection simple, enabling safe protection, and suggest a new paradigm of constructing quench-predictable superconducting magnets from Bi-2212.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Prediction of the J C (B) Behavior of Bi-2212 Wires at High Field

Bi-2212 wires have been produced for much of the last decade with varying architectures, powder sources and great variability of final J c (B) properties. As Bi-2212 transitions from an R&D materials development to a magnet technology, means to predictably forecast J c (B) become increasingly valuable. Here we report on characterizations of short samples having J c (15T, 4.2 K) varying from 1210 to 6560 A/mm 2 , measured in fields up to 31 T, and drawn from 10 billets. Using both 4 K transport and variable temperature VSM measurements capable of probing the 20 K irreversibility field, B irr = μ 0 H k , we discovered that the vortex pinning properties are very stable across these wires, which all used the same standard powder composition (Bi 2.17 Sr 1.94 Ca 0.89 Cu 2.00 O 8+x ), even though it has been made by three different manufacturers over nine years. We conclude that a power-law fit J c ∝ B -α , where α = 0.280 (σ = 0.015), works well at 4.2 K over the field range of at least 3-30 T and that μ 0 H k (20 K) remains stable at 8.6 ± 0.4 T. We conclude that the dominant current limiting mechanism predicting J c (B) in Bi-2212 is the effective filament connectivity. J c (B) at high fields may thus be predicted by simple I c measurements at easily accessible fields in the 3-15 T range.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High-Performance Bi-2212 Round Wires Made With Recent Powders

Multifilamentary Bi 2 Sr 2 CaCu 2 O x (Bi-2212) wire made by the powder-in-tube technique is the only high-temperature superconductor made in the round shape preferred by magnet builders. The critical current density (J C ) of Bi-2212 round wire was improved significantly by the development of overpressure heat treatment in the past few years. Bi-2212 wire is commercially available in multiple architectures and kilometer-long pieces and is a very promising conductor for very high-field NMR and accelerator magnets. Here, we studied the effects of precursor powder and heat treatment conditions on the superconducting properties and microstructure of recent Bi-2212 wires. Short samples of recent wire with optimized overpressure processing showed J C (4.2 K, 15 T) = 6640 A/mm 2 and J C (4.2 K, 30 T) = 4670 A/mm 2 , which correspond to engineering critical current densities J E (4.2 K, 15 T) = 1320 A/mm 2 and J E (4.2 K, 30 T) = 930 A/mm 2 .

36 MATERIALS SCIENCE↗