A Scalable APC Approach to Increase Layer and non-Cu Critical Current in High Field in Nb3Sn Conductors
- Hyper Tech Research, Inc., Columbus, OH (United States)
- The Ohio State Univ., Columbus, OH (United States). Center for Superconducting and Magnetic Materials (CSMM)
During Phase I, we succeeded in making Nb3Sn APC subelements and restacks with refined grain size in the reacted A15, and made the Nb3Sn APC subelements into 61-subelement restack strands and drew them down to 0.25 mm with subelement size of 25μm respectively. This is a big achievement. Due to the time limit of the Phase I, we have not optimized the heat-treatment and layer Jcs for the strand yet but will continue to work on this optimization. Nevertheless, even at this point the layer Jcs in the un-optimized multifilaments are 6800 A/mm2 at 4K-12T. While not yet at the 10,000 A/mm2 seen for the subelement, this is well within reach. This is because we used a modified pre-HT for the multi-strand which was too fast (due to time pressures). We believe that a lower ramp rate pre-HT (matching that used for the subelement) will achieve the full reduction of 40-50 nm in grain size and 10kA/mm2 at 4K-12T just as we saw for the subelements used to make the restack. As mentioned above we obtained both magnetic and transport Jc at 10,000 A/mm2 at 12T-4.2K in the binary APC Nb3Sn subelements, the basis for the above-mentioned restack. We have modified the present design for a better Sn-SnO2/Nb ratio for increased phase formation, and have fabricated and are currently heat-treating a 61 subelement strand version of this conductor, that we believe will produce the 30-50 nm grain Nb3Sn and obtain high Je as well as Jc. We also estimate that these values can be pushed significantly higher with new designs which should allow the practical introduction of ternary alloying. As will be described below, we will use tried-and-true methods for Ti injection into APC Nb3Sn strands. As we project into the proposed Phase II program, we will first optimize the heat-treatment schedule of the restack wires in Phase I, and then further optimize the chemistry in the subelement. We will make 217-subelement restack strands of this optimized subelement and draw it down to 0.7 mm with subelement size of 35 μm. We will demonstrate a further variant of the basic approach where Sn-oxide powder only will be placed in Nb-Zr alloy tubes to make a filament. These filaments will be used to construct Tube-like subelements which can be restacked to form pseudo-tube approach strands. We will also demonstrate a third route where a mixed powder/internal Sn route is employed. Both of these two new proposed designs allow for easier ternary alloying. Through this Phase II, we will fabricate strands targeting to double the Je performance of the best presently available conductor at 15 T and 16T.
- Research Organization:
- Hyper Tech Research
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- SC0013849
- OSTI ID:
- 1579553
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DE-SC0013849
- Country of Publication:
- United States
- Language:
- English
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