Conductor Requirements for Magnet Designers DOE Conductor Development
- Slides: 24
Conductor Requirements for Magnet Designers DOE- Conductor Development Program Daniel R. Dietderich Superconducting Magnet Program ICFA Mini Workshop on High Field Magnets for Future pp Colliders Shanghai Jiao Tong University, Xuhui Campus June 14 -17, 2015 Office of Science
A focused set of Grand Challenge questions addressing the P 5/HEPAP subpanel report concerns have been identified • Achieve a field of 16 T in a bore of at least 50 mm by focusing on simple, manufacturable designs Dr. X. Wang will address technology development in next talk • Understand training of Nb 3 Sn magnets and develop ways to reduce or eliminate it • Produce an HTS (Bi-2212/YBCO) insert with a self-field of > 4 T and measure the field quality • Reduce cost and improve performance of Nb 3 Sn • Increase the current density by 30% with a scalable sub-element structure • Aim for a cost per kg the same as Nb. Ti • Develop HTS conductor • Reduce silver (i. e. increase Bi-2212 content) or replace silver • Increase Jc/Je • Focus on magnets as technology drivers to generate larger market for cost reduction (Stewardship activity) as a collateral benefit to the program. ATAP SMP is uniquely qualified to address these challenges. June 15, 2015 2 D. R. Dietderich, LBNL
Conductor for Hi-Lumi LHC ITER strand: Non-Cu Jc 800 A/mm 2 (12 T, 4. 2 K) Critical current density versus field 2450 A/mm 2 Hi-Lumi strand: Non-Cu Jc 2500 A/mm 2 (12 T, 4. 2 K) RRP 132/169 1340 A/mm 2 PIT 192 ITER A. Ballarino June 15, 2015 3 D. R. Dietderich, LBNL
LARP Nb 3 Sn Specification The 150 mm aperture QXF magnet program in LARP is initially using the RRP 108/127 Ti-Ternary strand. Strand specification Strand Diameter, mm Jc(12 T) at 4. 2 K, A/mm 2 Ic , A Jc(15 T) at 4. 2 K, A/mm 2 Ic , A ds, µm (nominal) Cu-fraction, % Cu/non-Cu RRR Piece length June 15, 2015 0. 85 > 2650 > 684 > 1400 > 361 < 60 > 53 > 1. 13 > 150 > 750 m 4 D. R. Dietderich, LBNL
FCC Nb 3 Sn Requirements CDP is now focusing on conductor needs beyond High Luminosity LHC June 15, 2015 5 D. R. Dietderich, LBNL
Conductor Priorities for 20 T • Reduce cost – Need to reduce cost of Nb 3 Sn and Bi-2212 – Can billets be scale-up • ~ 200 kg billets Nb 3 Sn, perhaps 50 kg for Bi-2212 • Need to establish process early • Increase piece length • Reduce subelement size (filament ) – Single re-stack or Double re-stack • Increase Critical Current Density (Jc) – Need to understand the origin of Jc variation between identical wire – Need to understand Nb 3 Sn formation – Need to understand loss of Jc as the wire diameter decreases – Shift pinning curve June 15, 2015 6 D. R. Dietderich, LBNL
Rounder Nb Filament • Better piece length • Perhaps better performance (Higher Jc ) June 15, 2015 7 D. R. Dietderich, LBNL
ATI - Nb Grain Structure Heat A Heat C OST working with ATI To improve Nb rods Rod Micrographs Nb Type 1 Edge of billet Center of billet Courtesy of Phil Olarey Microstructure can be vary across a billet ATI developing processing to improve uniformity June 15, 2015 8 D. R. Dietderich, LBNL
RRP® with more sub-elements Smaller Filament Size RRP® 54/61 RRP® 192/217 721 to 919 ~ 20 mm June 15, 2015 9 D. R. Dietderich, LBNL
CDP -- RRP® 192/217 Properties No SF correction CDP billet 14832 650 C/50 hrs 30 m • RRR, Jc, and n-value decrease with decreasing wire diameter • Can reduce Sn to increase RRR • Reduced Sn may permit the 30% thicker barrier to be used in a 252/271 stack or greater – 37 µm sub-elements at 0. 85 mm June 15, 2015 10 D. R. Dietderich, LBNL
Sub-element Diameter, m • L. Cooley & A. Ghosh Formalization • LARP and OST Standard R=Cu/Non-Cu=1. 15 , 46. 5% SC, 53. 5 % Cu June 15, 2015 11 D. R. Dietderich, LBNL
Subelement Number • What sub-element size is needed for HE-LHC and future machines? • For a wire diameter of 0. 85 mm • Stack = Subelement size 271 = 42 mm 271 = 37 mm. . 721 to 919 ~ 20 mm Can this be produced? • If billet starting diameter is ~100 mm (4”) • Subelement diameter during billet fabrication is 3 -4 mm • At this size they are difficult to handle June 15, 2015 12 54/61 RRP® Perhaps cold extrusion for 6 -8” diameter billet D. R. Dietderich, LBNL
Formation of Nb 3 Sn – Re-design of RRP® Sub-element • Re-visit the design of the RRP® subelement – Cu channels between filaments – Nb filament diameter – Barrier thickness and uniformity • Subelement will start to approach a tubular process • Jc decreases significantly for Ds below ~50 m – Need better understanding of tin / bronze diffusion and the interaction with Nb-Sn-Cu ternary as Ds↓ RRP reacted 210°C/48 hr + 400°C/48 hr, Courtesy of FSU (Peter Lee, Charlie Sanabria) • Collaborations with Sanabria (FSU), Pong (LBL) June 15, 2015 75 m 20 m 13 D. R. Dietderich, LBNL
Methods to Reduce Cost and Magnetization • Single barrier approach • ITER style conductor – Single barrier approach – Has lower magnetization and cost than RRP® – However, Jc is low • This would require an increase of the layer Jc – Increasing flux pinning – Recent work by OSU and Hyper Tech • No clear path to final conductor! June 15, 2015 14 D. R. Dietderich, LBNL
Double Re-stack • A “double restack” – restacking the restack – can access the smaller Ds at the desired wire size range – Need subelements tolerant to a high degree of deformation – Difficult to keep the Non-Cu fraction and Ic up, • Double restacking adds in extra copper 7 stack X 61 stack = 324 Ds ~ 20 m @ 0. 8 mm Perhaps one could cold extrusion a 6”-8” diameter billet June 15, 2015 15 D. R. Dietderich, LBNL
Conductor Performance Improvement • Need to increase current density at higher fields • Nb 3 Sn - Shift pinning curve in wires to higher fields – Develop conductor with smaller grain Nb 3 Sn • Bi-2212 – Need to reduce porosity – Improve filament continuity Nb 3 Sn Target JE ~ 600 A/mm 2 Bi-2212 A. Godeke June 15, 2015 16 D. R. Dietderich, LBNL
J of wire for Pinning Curve Shift Godeke, et al. , unpublished Nb 3 Sn Target JE ~ 600 A/mm 2 Hc 2? June 15, 2015 17 New work Xingchen Xu of OSU and Hyper Tech on wires may be shifting the curve D. R. Dietderich, LBNL
Shift Pinning Curve of Nb 3 Sn Films of Nb 3 Sn with “Engineered Microstructures” Grain size ~ 75 nm Dietderich and Godeke, Cryogenics 48, 331 (2008) June 15, 2015 18 Grain size ~ 20 nm Inclusions ~ 5 nm D. R. Dietderich, LBNL
Bi-2212 With Over Pressure Godeke, et al. , unpublished Target JE ~ 600 A/mm 2 Bi-2212 Magnet target has been achieved with overpressure processing June 15, 2015 19 D. R. Dietderich, LBNL
Material Properties • Conductor Development Program of HEP • Nb 3 Sn: – Understand strain behavior RRP Nb 3 Sn • Bi-2212 – Develop a high quality powder supplier – Increase critical current by exploring other powder compositions. – Improve strain tolerance of wire – Cable stress A. Godeke Ic drops at 60 MPa June 15, 2015 20 D. R. Dietderich, LBNL
Bi-2212 Goals • Reduce Cost – Bi-2212 needs a market other than HEP – Scale up billet size • Can the amount of superconductor in wire cross section be increased? – Improve stress and strain tolerance – Area is now ~25%, need ~50% • Would this lead to processing issues since Bi-2212 powder has not strength? – This would double critical current of a wire for the approximately the same cost – Past wires with 50% Ag showed NO increase in Ic June 15, 2015 21 D. R. Dietderich, LBNL
Bi-2212 Effort in CDP • For a 1. 2 mm diameter wire with a stack of 85 x 18 – No loss of critical current for twists lengths down to 12 mm • Increase strength of wire – Increase Ag alloy fraction in wire from ~24% to ~42 % • Could lead to more Bi-2212 in cross section • With over-pressure the wire Jc(4. 2 K, 12 T) is about the same as that of a std. wire June 15, 2015 Ag alloy (blue) 22 D. R. Dietderich, LBNL
Bi-2212 Future Directions • Concern about supply of high quality Bi-2212 powder – Supporting a Task to fabricate wires from the different powder suppliers • “ 521” composition has been the standard for many years – Can the critical current be increased by obtaining a better understanding of why it seems to be the best? – Or composition developed before? • 522, 523, & 524 developed by OST and Nexans • Try new compositions – Over pressure processing may require different composition • Improve filament continuity • The effective filament size of a wire is large: How can it be reduced? June 15, 2015 23 D. R. Dietderich, LBNL
End June 15, 2015 24 D. R. Dietderich, LBNL
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