Innovation with Integrity Klaus Schlenga Washington, March 25, 2015 Bruker response to the FCC specifications

Innovation with Integrity Outline  Bruker Nb 3 Sn wire portfolio and production statistics  State of the Art PIT Performance  Comparison of FCC conductor target list to current PIT performance  Interplay filament diameter – Jc – RRR  Requirements and ideas for improved PIT design  Dedicated R&D program 2

Innovation with Integrity Nb 3 Sn Conductors at Bruker  Bruker EAS has long time experience in development and manufacturing of Nb 3 Sn superconductors.  This comprises fabrication of Nb 3 Sn conductors by different manufacturing routes: o Internally Stabilized Bronze Route: o Internal Tin Route: 1986 – 1990 o Outer Stabilized Bronze Route: 1980 – today o Powder In Tube Route: today 3

Innovation with Integrity Production Statistics  Main focus of R&D at Bruker is to achieve highly reliable performance levels of conductors. This can only been reached by robust and controllable industrial fabrication processes. 4

Innovation with Integrity Production Statistics  Main focus of R&D at Bruker is to achieve highly reliable performance levels of conductors. This can only been reached by robust and controllable industrial fabrication processes. 5 Fabrication of ≈ 38 t of Bronze Route Nb3Sn strand for ITER Variation of total production jc: average 811 A/mm², 3 σ < 7 %

Innovation with Integrity Production Statistics  Main focus of R&D at Bruker is to achieve highly reliable performance levels of conductors. This can only been reached by robust and controllable industrial fabrication processes. 6 Fabrication of PIT192 – Ø = 1.00 mm

Innovation with Integrity State of Art Performance of PIT Nb 3 Sn wires - spread  Jc Performance of PIT192 NbTa filaments Ø = 1.00 mm Ic, max (4.2 K, 15 T) = 511 A; Cu / non Cu = 1.31, RRR = 177, B c2 * = 26.5 T Ic, min (4.2 K, 15 T) = 453 A; Cu / non Cu = 1.33, RRR = 240, B c2 * = 26.4 T 7

Innovation with Integrity State of Art Performance of PIT Nb 3 Sn wires - spread  Jc Performance of PIT192 NbTa filaments Ø = 1.00 mm Ic, max (4.2 K, 15 T) = 511 A; Cu / non Cu = 1.31, RRR = 177, B c2 * = 26.5 T Ic, min (4.2 K, 15 T) = 453 A; Cu / non Cu = 1.33, RRR = 240, B c2 * = 26.4 T 8 after reaction powder core reaction front outer filament contour Spread in electrical performance is an interplay between jc and RRR. It can partially be explained by different usage of the "real estate" of the filament cross section.

Innovation with Integrity Target FCC specification for Nb 3 Sn strand 9 A. Ballarino, L. Bottura, ASC 2014, 3MSPa-06, to be published in IEEE TAS Continuous reduction (NED-FRESCA2-HL-LHC) of strand diameters in HEP specifications and reduction of filament diameters observed. These reductions impact the feasibility of achieving the electrical targets. The electrical performance data have now shifted to 16 T and magnetization is introduced.

Innovation with Integrity Comparison of PIT192 Ø = mm strand to target FCC specification  Best performing PIT192 Ø = 1.00 mm strand compared to target specification. o The required increase in j c (including margin!) needs to be achieved having the reduced filament diameters and small strand dimensions as constraints. o Robustness of strand for cabling is required A/mm²  Spec A/mm² + 22 % required

Innovation with Integrity Reduced filament diameter  Reducing filament diameters means (apart from desired decrease of magnetization): 11

Innovation with Integrity RRR vs. Jc with small filament diameters  … and will not only be a matter of heat treatment optimization! 12 Variation of heat treatments applied to strands with 34 µm and 29 µm respectively

Innovation with Integrity Implications for current PIT design  Reduction of strand and/or filament diameters of PIT wires with standard layout will lead to o More deformed filaments, due to grain size effects of the materials involved o Reduction of n value due to more inhomogeneous filaments o Reduced reliability of diffusion barrier (unreacted Nb tube) o More probable Sn contamination of the stabilizing Cu o More sensitivity to cabling induced deformation  Ic, n, RRR will suffer from these effects, thus new layouts become mandatory to reduce their impact. 13

Innovation with Integrity Requirements for future PIT design  Stabilizing Cu needs to be reliably protected  Enhancing jc, non Cu by improved usage of the Nb 3 Sn area of the filament cross section  Enhancing the "quality" of the Nb 3 Sn by better understanding/control of the reaction  Extensive R&D and analytical work exclusively dedicated for this application will be required to achieve the targets  Reasonable margin above the specified values needs to be assured for high yield 14

Innovation with Integrity R&D program for improved Nb 3 Sn strand 15  FCC will be a unique challenge and opportunity for Nb 3 Sn strand.  Bruker EST will support this challenge but adequate funding must be secured.  To address FCC needs the strand manufacturer needs to have enough degrees of freedom to play with.  The more stringent the specification is, the less the chance to develop a strand that enables the fabrication of magnets for FCC on justifiable cost  An iterative R&D program with milestones and possible compromises and flexibility regarding performance along the way might be necessary!

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