High Temperature Superconductor Cable Concepts for Fusion Magnets by Christian Barth \iyit Scientific ^VI I Publishing
Contents 1 Introduction and motivation 1 2 Superconductors 5 21 Superconductivity 5 211 Type I and type II superconductors 5 212 Critical values 8 2121 Critical temperature 8 2122 Critical magnetic field 8 2123 Critical current density 9 2124 Operating parameters 10 213 Technical superconductors 12 22 Low temperature superconductors 13 221 Niobium-titanium (NbTi) 13 222 Niobium-tin (Nb3Sn) 15 23 High temperature superconductors 16 231 Bismuth-strontium-calcium-copper-oxide (BSCCO) 2223 tapes 17 232 Bismuth-strontium-calcium-copper-oxide (BSCCO) 2212 round wires 18 233 Rare-earth-barium-copper-oxide {REBCO) tapes 19 2331 Composition and manufacturing of REBCO 20 2332 Properties of REBCO 21 2333 Production of REBCO 26 2334 Outlook on production and performance of REBCO tapes 26 24 Comparison of superconductors and their usability for fusion magnets 27 3 Superconducting fusion magnets 29 31 Introduction to fusion 29 311 Magnetic confinement 29 312 Development of magnets for controlled fusion 31 313 State-of-the-art of fusion magnet technology 32 3131 Cable-in-conduit conductors 32 3132 Challenges in fusion magnets 35 v
32 Main parameters of fusion power plants 38 33 Conductors in fusion power plants 42 331 Electrical and mechanical requirements 42 332 Cooling options 45 333 Nuclear activation 48 34 Potential of high temperature superconductors in fusion magnets 50 4 Materials of high temperature superconductor cables 53 41 Thermal expansion 53 411 Experimental setup 54 412 Measurement uncertainty 57 413 Characterized materials 57 414 Results 58 4141 Structural materials 59 4142 Insulating materials 59 4143 Filling materials 60 415 Summary and recommendation for HTS cables 61 42 Degradation free impregnation 63 421 Thermal expansion 64 4211 Characterized materials 64 4212 Results 65 4213 Measurement uncertainties 67 422 Degradation measurements on short REBCO tapes 68 4221 Measurement procedure 68 4222 Results 70 423 Validating results on an HTS cable 71 424 Summary 73 43 Thermal conductivity 75 431 Experimental setup 76 432 Measurement uncertainty 78 433 Characterized materials 79 434 Results 80 4341 REBCO tapes, parallel to the tape 80 4342 REBCO tapes, perpendicular to the tape 81 4343 Structural and insulating materials 82 4344 Filling materials 83 435 Summary and on impact HTS cables 84 VI
no 5 Roebel Assembled Coated Conductor (RACC) cables 87 51 Introduction 87 52 High temperature superconductor Roebel cables 88 521 Manufacturing of HTS Roebel cables 88 53 Optimizing the geometry of the meander structure 90 531 Parametrization of the meander structure 91 532 Influence of geometric parameters on mechanical properties 92 5321 Simulation method 92 5322 Simulation results 93 5323 Impact on Roebel geometry 96 533 Influence of geometric parameters on current density 97 5331 Simulation method 97 5332 Simulation results 99 5333 Impact on Roebel geometry 102 534 Summary and recommendation 103 54 Optimizing the contacts of HTS Roebel cables 104 541 State-of-the-art 104 542 Soldering methods 106 5421 Coating copper with solder 107 5422 Coating REBCO tapes with solder 107 543 Individually contacted tapes 108 544 Performance of individually contacted RACC cables 110 545 Summary and recommendation Ill 6 High temperature superconductor fusion magnet cable concepts 113 61 Experimental setup 114 611 The FBI test facility 114 612 Temperature variable insert 115 6121 Layout 116 6122 Validation 117 613 Assessment 119 62 Roebel Assembled Coated Conductor (RACC) cable 119 621 Composition 120 622 Mechanical properties 120 623 Field and temperature dependent measurements 121 6231 10 strand RACC - epoxy impregnation 122-6232 15x5 RACC epoxy resin impregnation 123 6233 In-field tests at CERN 125
624 Scaling to currents relevant for fusion magnets 126 6241 Extrapolation with present REBCO tape performance 127 6242 Corresponding RACC cables 128 625 Contacts 129 63 Coated Conductor Rutherford Cable (CCRC) 130 631 Composition 130 632 In-and out-of-plane bending 131 633 Current carrying capabilities of a sub-size CCRC 132 634 Scaling to currents relevant for fusion magnets 133 635 Contacts 134 64 Conductor on Round Core (CORC) cable 134 641 Composition 134 642 Mechanical properties 135 643 Field and temperature dependent measurements 136 6431 LNi characterization 137 6432 In-field measurements 138 644 High current ramping rates 140 645 Temperature distribution 141 646 Scaling to currents relevant for fusion magnets 143 647 Contacts 146 65 Twisted Stacked-Tape Cable (TSTC) 146 651 Composition 146 652 Mechanical properties 148 653 Field and temperature dependent measurements 149 6531 Critical current measurements at increasing and decreasing magnetic fields 150 6532 Temperature dependence at different background fields 152 654 Temperature distribution 153 655 Scaling to currents relevant for fusion magnets 154 656 Contacts 156 66 Round Strands Composed of Coated Conductor Tapes (RSCCCT) cable 157 661 Composition 157 662 Scaling to currents relevant for fusion magnets 158 663 Contacts 159 67 Comparison of HTS cable concepts 159 68 HTS winding packs for fusion magnets 163 681 HTS winding pack for ITER 164
6811 Calculation method 166 6812 Results 168 682 Winding packs for fusion power plants 169 6821 Calculation method for LTS 169 6822 Comparison with HTS 170 683 Summary 171 7 Summary 175 A Annex 179 Al Anisotropic strain effect of REBCO tapes 179 A 11 Single REBCO crystals 179 A 12 REBCO tapes 179 A2 Influence of shear stress on the current carrying capabilities of HTS tapes 181 A21 Experimental setup 181 A22 Finite element method calculations 182 A23 Results 184 A3 Normalized critical currents of Nb^Sn and REBCO at different magnetic fields 185 A4 Fitting parameters of the field and temperature dependent tests of CORC cables 186 A5 Scaling behavior of CORC cables 186 A6 Fitting parameters of the field and temperature dependent tests of TSTCs 189 B Designations and abbreviations 191 C Index of symbols 195 D Bibliography 201