Evaluation of Joint Resistance Between Bi-2223/Ag Superconducting Tapes
We fabricated Bi-2223/Ag jointed tape and evaluated its current carrying capacity and joint resistance at 77.3 K as a function of the contact length. The tapes were jointed by the conventional resistive joint method with 40Pb-60Sn solder as an insert material and their joint resistance was measured by two different techniques, i.e., the standard four-probe and field decay methods. It was observed that the current carrying capacity and joint resistance were significantly dependent on the contact length. As the contact length increased, the current carrying capacity improved and increased to the level of critical current in the unjoined tape at the contact length of 5 cm. On the other hand, the joint resistance linearly decreased as the contact length increased. In addition, the joint resistances measured by the two methods were similar to each other (7.3times10-9 Omega~8.0times10-9 Omega), indicating that the standard four-probe method maintained a moderate degree of accuracy at the level of resistance of 10-9 Omega
Design and Fabrication of a Hybrid HTS Magnet for 150 kJ SMES
Abstract
This paper describes design and fabrication of a hybrid high temperature superconducting (HTS) magnet for a 150 kJ superconducting magnetic energy system. The hybrid HTS magnet, which employs both BSCCO taps and YBCO taps, is composed of 18 double pancake coils (DPC). Six DPC made of BSCCO are respectively installed on the top and bottom with an inner diameter of 240 mm, an outer diameter of 396 mm, and height of 11.5 mm. Six YBCO coils are mounted in the middle of the magnet with the inner and outer diameters of 264, 396 mm and height of 12.1 mm. Copper plates with thickness of 1 mm are arranged between DPC for the cooling of the heat, and epoxy resin plates with thickness of 0.2 mm are arranged between coil and copper plate for the insulation. The inductance of the magnet is about 11.06 H and the resistance is 169.5 Ω at the room temperature. In order to evaluation the performance of the hybrid magnet, each solidified DPC and the assembled magnet were tested in a bath of liquid nitrogen at 77 K. The resistances of 17 joints were also measured and evaluated by the standard four-probe method.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.