Bruker tape (T053) analysis for Roebel cable A.Kario, B. Ringsdorf, A. Kling, B. Runtsch, A. Jung, R. Nast, W. Goldacker (KIT, ITEP) 1

As delivered Bruker tape: 2

12 mm wide 1.3 m long 800 € Bruker tape – preis ? 3

Homogeneous Cu on the side of REBCO: Grain size: 18 µm Homogenous layer of copper on REBCO side 4

Inhomogeneous Cu on the side of substrate: 11 µm deep holes in copper on the substrate side Inhomogeneous copper layer on the substrate tape 5

Tape cross section (SEM, laser cut): µm 67.4 µm 71.2 µm µm 34.1 µm µm 19.5 µm SC: 1.82 µm 102 µm 25.4 µm Substrate SS 100 µm YBCO: 1.8 – 2 µm thick Uneven copper thickness on the tape top and bottom: µm Dog-bone effect, uneven tape thickness: 146 – 270 µm Tape width – copper layer on the edge – 100 µm wide 6

19.9 µm 23 µm 146 µm Uneven tape thickness, middle part: 146 µm Copper layer on the side of substrate: two layers of copper – with different grain size, why? Tape cross section and top view (SEM, laser cut): 7

Short sample I c in LN 2 s.f. : Short piece of samples 2 x 8 cm Homogeneous tape I c along and across 8

1 m long tape 10 cm distance between voltage taps Sample measured before and after punching 50-74% I c degradation after punching Long sample - non homogeneous I c in LN 2 s.f. before and after punching: * I c not measured before punching * 10 cm 20 cm 10 cm 9

20 cm 10 cm Long sample (1 m) after punching - defect due to Non - homogeneous width: 10

Tape edge after punching: Punching direction Punching direction No defects or delamination after punching and 3 x I c measurement at LN 2 11

Summary: Low, not homogeneous I c along tape (LN 2, s.f.) Short piece of the tape. For Roebel test at 4.2 K: 30 m long tape required (if FRESCA test planned) Tape not suitable due to thick stainless steel substrate and tape strain (6 cm diameter) – low flexibility for cable assembly Tape thickness result in smaller no. of strands in Roebel cable (tape thickness: 0.1 vs. 0.3 mm) Inhomogeneous width of the tape result in defects during punching! Inhomogeneous thickness of the tape – strong dog-bone effect Analysis of punched structure: no signs for delamination after I c measurement and SEM pictures 12