HTS Roebel cables N.J. Long, Industrial Research Ltd and General Cable Superconductors Ltd HTS4Fusion Workshop, 26 May 2011
Contents Cable dimensions Wire qualification Manufacturing Punching Retained I c Winding Performance Current contacts Cable I c results Potential performance I c -stress Coupling Insulation options Conclusions
HTS Roebel Cable Dimensions Cables are labelled with the convention # of strands / strand width We are making two designs 15/5 and 10/2 More strands longer transposition length
Wire qualification For Roebel we require 2D uniformity 0.023 T (a) (a) Field (T) - Scan wire magnetically (penetrated or remnant field) - Quantify uniformity using statistical correlation with an ideal magnetic profile Correl( X, Y ) = Where Correl 1 0.030 0.025 0.020 0.015 ( ( x x)( y y) x x) 2 ( y y) X is a dataset representing calculated field Y{y 1 y j } is magnetic data across tape Example Profiles 0.040 cor_0.99 cor_0.90 0.035 cor_0.75 2 0.000 T Correlation along a length of YBCO wire, a minimum Correl can be specified for input wire Correlation 1.00 0.98 0.96 0.94 0.92 200mm Use magnetic imaging to assess tape quality (a) tape with a known defect, and (b) tape with only small scale variability. Some wire is extremely good! Wire 2 (b) 0.010 0 2 4 6 8 10 12 Position (mm) 0.90 0 10 20 30 40 50 Position (m)
Automated punching Tape de-spool Punch tool and frame L trans must have minimal error to enable long length winding Cutting tool is state-of-the-art Pattern is fixed by tooling Tool wear is negligible Control systems Tape re-spool Wider feedstock less waste Punching patterns b) c) and d) have all been done (a) (b) (c) 10 strands cut from 40 mm AMSC strip (a) 4 x 5 mm strands from 40 mm (b) 1 x 5 mm wide strand from 12 mm (c) 10 x 2 mm strands from 40 mm (d) 3 x 2 mm wide strands from 12 mm (d)
Quality of punching Electroplated copper/niw Electroplated copper/niw AMSC 3 ply SS/NiW/SS AMSC 4 ply Cu/2x NiW/Cu
Retained I c Strands maintain the wire performance (I c strand) / (I c wire) ~ typically 90-95%, can be 110% High minimum value of Correl is necessary but not sufficient condition I c also needs to be considered Length of defect important Scaling to low T, defects look like a cross sectional loss of conductor Can we mitigate low Correl values? Strand reinforcement is OK for high I/Ic Added section of wire (soldered) defect
Automated Cable Winding Planetary wind Longitudinal phase very important Set up is important Every wire guided carefully into place In principle can be fast ~ meters/min At present we go slow We have $$$ at risk Automated planetary wind system for 15/5 cable
Current contacts Place cable in copper block Apply solder to excess Heat and apply pressure to flow solder Cool down, then remove pressure Apply solder with excess to fill interstrand gap HTS Surface down -Direct contact with largest copper cross section
Cable I c test
I c measurement of cables Cable details Cable I c (A) Design I c Measured Computed 5/2 252 203 220.1 9/2, d = 136 µm 426 318.8 339.1 9/2, d = 350 µm 426 341.9 359.1 15/5, d = 160 µm 15/5 cable from SuperPower wire 15/5 SRC0024, d = 100 µm 1454 1616 1100 1010 1033 1109 15/5 SRC0027, d = 100 µm 2093 1410 1372 Measured I c has been close to expected I c For short length cables accurate I c measurement is difficult At 77K there are strong self-field effects Calculation using method of K Thakur et al, Physica C 471, 42-47
Expected I c at high fields (15/5 cable) 10000 I c (A) 1000 100 4.2K, 14K, 22K, 33K 45K, 50K, 65K 0 5 10 15 Perpendicular Field (T) The data is generated using the following assumptions Self-field performance of wire is scaled to higher fields using data from SuperPower We have assumed 280A/cm performance of wire (most current wires from SP meet or exceed this performance). Note the design current will be significantly reduced by the cable self field at fields < 1T 15/5 = 15 strands of 5mm width We do not have parallel field data at this time, parallel field I c is generally much higher than perpendicular field performance e.g. see http://www.htspeerreview.com/2008/pdfs/presentat ions/tuesday/joint/joint_2_scale_up_progress_supe rpower.pdf
I c longitudinal stress test 5/2 cable failed catastrophically at 453N (whilst still displaying 86% of maximum I c ) Roebel cable appears to exhibit identical ductile limit to Hastelloy tape The Roebel strands lock together suppressing torque at the transpositions Increasing the tensile strain greatly improves current sharing between strands (data not shown). Tensile ductile limit of Hastelloy 276 ~ 700MPa @77K. From Clickner et al. Cryogenics 46 432-438 (2006)
Strand coupling Cable coupled by copper bridges R ~ 10 µω Loss increasing then decreasing with frequency Fit to Debye form Γ (J m -1 cycle -1 strand -1 T -2 ) 7 6 5 4 3 2 1 1 10 100 B (mt) 30 Hz 59.5 Hz 120 Hz 175.5 Hz Γ (J m -1 cycle -1 strand -1 T -2 ) 6 4 2 5/2 coupled cable B = 2 mt 0 0 50 100 150 200 Frequency (Hz) The magnetization loss with the applied field The magnetization loss v frequency
Strand insulation Individual strands can be insulated with polymer coating to prevent current sharing Roll coater to insulate strands
Cable insulation Extrusion coating: fluorinated polymer Wrapping: kapton, nomex paper No in situ processing of wire flexible insulation options
Conclusions We have established a pilot plant with automated production of 10/2 and 15/5 cable Demonstrated strand coupling and strand insulation Obtained first results on stress-i c properties Magnetisation and transport AC loss results published Measurements on coil properties including AC loss in progress Likely route to low cost Roebel cable is through manufacture of wide REBCO strip Cable manufacture equipment at IRL site