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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Fragmentation of faceted crystalline wires

The reduction of surface energy is a well-known driving force for the fragmentation of nanowires. Fragmentation can limit the service life of those small low-dimensional building blocks or can be controlled to induce beneficial shape changes. For isotropic surface energy, fragmentation is analogous to the classic Rayleigh-Plateau instability of liquid jets. However, commonly synthesized crystalline nanowires have strongly anisotropic surface energies and exhibit facets coinciding with cusps in the Wulff plot. Depending on growth orientation, different fragmentation behaviors have been seen in nanowires. Using phase-field simulations, we show that fragmentation of faceted nanowires with cubic crystal symmetry may occur by a finite-amplitude nonlinear instability, as opposed to a Rayleigh-Plateau-like linear instability, depending on nanowire growth orientation. Here, we carry out a weakly nonlinear analysis based on sharp interface theory to characterize the faceted nanowire shape corresponding to a surface-energy saddle point. The analysis predicts that the minimum amplitude of a periodic shape perturbation to trigger fragmentation increases with cusp strength but decreases inversely proportionally to the perturbation wavelength for long wavelengths, in good quantitative agreement with phase-field predictions. The results provide the theoretical foundation to predict nanowire stability as a function of length and surface energy in diverse applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Development and Study of Nb 3 Sn Wires With High Specific Heat

Recently, a new type of Nb 3 Sn conductors were developed, which, by incorporating substances with high specific heat at 2-8 K in a proper design, have demonstrated significant improvement of minimum quench energy (MQE). This method to improving energy margins of conductors is promising to reduce Nb 3 Sn magnet training. Here, we continue studying this type of conductors. Voltage-current (V-I) measurements from 15 T to 0 T and voltage-field (V-B) sweeps at various currents were conducted to investigate the influence of increased specific heat on the intrinsic stability of Nb 3 Sn conductors. Normal zone propagation velocity (NZPV) was also studied. Lastly, a new scheme was put forward to introduce a new type of substances with not only high specific heat but also high thermal diffusivity to Nb 3 Sn conductors, which is expected to work more effectively.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Re-Assembly and Test of a COMB Dipole Magnet With STAR Wires

Rare-Earth Barium Copper Oxide (REBCO) coated conductors are an attractive option for application in high field accelerator magnets due to their high critical field and the convenience of fabrication without heat treatment compared to some other superconductors. A small REBCO accelerator magnet was previously fabricated and tested in liquid nitrogen, demonstrating over 90% critical current retention in the coils. This paper describes the magnet re-assembly with a different support structure and its test in liquid helium at 1.8–4.5 K. The magnet quench history along with the instrumentation data is presented and discussed.

43 PARTICLE ACCELERATORS↗