Transport and magnetic Jc of MgB2 strands and small helical coils

The critical current densities of MgB2 monofilamentary strands with and without SiC additions were measured at 4.2 K. Additionally, magnetic Jc at B = 1 T was measured from 4.2 K to 40 K. Various heat treatment times and temperatures were investigated for both short samples and small helical coils. SiC additions were seen to improve high field transport Jc at 4.2 K, but improvements were not evident at 1 T at any temperature. Transport results were relatively insensitive to heat treatment times and temperatures for both short samples and coils in the 700C to 900C range.Comment: 8 text pages, 1 table, 4 fig

A large-scale validation study of aircraft noise modeling for airport arrivals

In the U.S., the Federal Aviation Administration's Aviation Environmental Design Tool (AEDT) is approved to predict the impacts of aircraft noise and emissions. AEDT's critical role in regulatory compliance and evaluating the environmental impacts of aviation requires asking how accurate are its noise predictions. Previous studies suggest that AEDT's predictions lack desired accuracy. This paper reports on a large-scale study, using 200 000 flight trajectories paired with measured sound levels for arrivals to Runways 28L/28R at San Francisco International Airport, over 12 months. For each flight, two AEDT studies were run, one using the approved mode for regulatory filing and the other using an advanced non-regulatory mode with exact aircraft trajectories. AEDT's per aircraft noise predictions were compared with curated measured sound levels at two locations. On average, AEDT underestimated LAmax by -3.09 dB and SEL by -2.04 dB, combining the results from both AEDT noise-modeling modes. Discrepancies appear to result from limitations in the physical modeling of flight trajectories and noise generation, combined with input data uncertainties (aircraft weight, airspeed, thrust, and lift configuration) and atmospheric conditions

Large Upper Critical Field and Irreversibility Field in MgB2 wires with SiC additions

Resistive transition measurements are reported for Magnesium diboride strands with SiC dopants. The SiC was added as 10 mol of SiC to 90 mol of binary magnesium diboride. Three different SiC powders were used, the average particle sizes were 200 nm, 30 nm, and 15 nm. The strands were heat treated for times ranging from 5 to 30 minutes at temperatures from 675 to 900. Strands with 200 nm size SiC additions had Hirr and Bc2 which maximized at 25.4 T and 29.7 T after heating at 800C for 30 minutes. The highest values were seen for a strand with 15 nm SiC heated at 725C for 30 minutes which had a Hirr of 29 T and a Bc2 higher than 33

The critical current density of advanced internal-Mg-diffusion-processed MgB2 wires

Recent advances in MgB2 conductors are leading to a new level of performance. Based on the use of proper powders, proper chemistry, and an architecture which incorporates internal Mg diffusion (IMD), a dense MgB2 structure with not only a high critical current density Jc, but also a high engineering critical current density, Je, can be obtained. In this paper, a series of these advanced (or second - generation, "2G") conductors has been prepared. Scanning electron microscopy and associated energy dispersive X-ray spectroscopy were applied to characterize the microstructures and compositions of the wires, and a dense MgB2 layer structure was observed. The best layer Jc for our sample is 1.07x105 A/cm2 at 10 T, 4.2 K, and our best Je is seen to be 1.67x104 A/cm2 at 10 T, 4.2 K. Optimization of the transport properties of these advanced wires is discussed in terms of B-powder choice, area fraction, and the MgB2 layer growth mechanism.Comment: 13 pages, 3 tables, 7 figures (or 8 pp in published version

Doping Effect and Flux Pinning Mechanism of Nano-SiC Additions in MgB2 Strands

Superconducting MgB2 strands with nanometer-scale SiC additions have been investigated systematically using transport and magnetic measurements. A comparative study of MgB2 strands with different nano-SiC addition levels has shown C-doping-enhanced critical current density Jc through enhancements in the upper critical field, Hc2, and decreased anisotropy. The critical current density and flux pinning force density obtained from magnetic measurements were found to greatly differ from the values obtained through transport measurements, particularly with regards to magnetic field dependence. The differences in magnetic and transport results are largely attributed to connectivity related effects. On the other hand, based on the scaling behavior of flux pinning force, there may be other effective pinning centers in MgB2 strands in addition to grain boundary pinning.Comment: 22 pages, 9 figures, 1 tabl