FOREWORD vii

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INDEX

ACKNOWLEDGMENTS i

FOREWORD vii

1 THE FERMI NATIONAL ACCELERATOR LABORATORY

1.1 Introduction 1

1.2 High energy accelerators 2

1.3 The Tevatron 3

1.4 Superconducting Magnets 6

1.5 Superconducting Strand and Cable 9

1.6 The Next generation machines 10

1.7 Technical Division 12

1.7.1 High field superconducting magnets 12

1.7.1.1 Short Sample Test Facility 13

1.8 Other application of superconductivity 15

1.8.1 Magnetic resonance imaging 16

1.8.2 Energy storage 16

1.8.3 Controlled thermonuclear fusion 16

1.8.4 Magnetohydrodynamic power generation 17

1.8.5 DC motors and AC machines 17

1.8.6 Magnetic levitation 18

1.8.7 Power lines 18

1.9 Summary 18

2 SUPERCONDUCTIVITY

2.1 Introduction 20

2.2 Discovery of superconductivity 21

2.3 Two-fluid thermodynamic theory 23

2.4 Skin effect in superconductors 26

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2.5 Cooper Pairs 28

2.6 Flux Quantization 29

2.7 Type II superconductors 30

2.8 Magnetization of hard superconductor 34

2.9 Critical state model 34

2.10 Summary 36

3 INSTABILITY

3.1 Introduction 37

3.2 Degradation and training 38

3.3 Copper stabilization 39

3.4 Flux jumping 40

3.4.1 Adiabatic stability criteria 41

3.5 Introducing the smoothness of the transition 41

3.5.1 Stability against electromagnetic disturbance 43

3.5.2 Stability against heat pulses 45

3.5.3 Limitations of models with smooth transition 47

3.6 Predicting quench currents 48

3.6.1 Heat generation during a flux jump 48

3.6.2 Instabilities in a strand without transport current 49 3.6.3 Instabilities in a strand with transport current 51

3.6.4 Effect of Deff and Jc 53

3.7 Summary 54

4 SUPERCONDUCTING MATERIALS AND THEIR MANUFACTURE

4.1 Introduction 56

4.2 Superconductors for use in magnets 57

4.2.1 Filamentary composites 58

4.3 Niobium Titanium 59

4.4 Niobium Tin 61

4.4.1 The bronze process 63

4.4.2 The internal tin process 63

4.4.3 The modified jelly roll process 65

4.4.4 The restacked rod process and the hot extruded rod process 67

4.4.5 The powder in tube process 69

4.5 Summary 70

5 CRITICAL CURRENT MEASUREMENTS

5.1 Introduction 71

5.2 Experimental setup 72

5.2.1 The magneto-cryostat 72

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5.2.2 Electronics and data acquisition software 73

5.3 Sample preparation 75

5.4 Probe for critical current measurements 77

5.5 Experimental evaluation of I

c

and J

c

78 5.6 N-Value and Residual Resistivity Ratio 79

5.6.1 N-Value 79

5.6.2 RRR 80

5.7 B

c20

evaluation 81

5.8 Summary 82

6 EFFECT OF SAMPLE HOLDER RESISTANCE ON I

c

MEASUREMENTS

6.1 Introduction 83

6.2 High current measurement with the original probe 85 6.3 Total resistance measurements of the original sample holder 85

6.3.1 Introduction 85

6.3.2 Error analysis 87

6.3.3 Total resistance 88

6.3.4 Extrapolation of the maximum current capability 90 6.4 Individual resistance measurements of the original sample hold 94

6.4.1 Error analysis 94

6.4.2 Copper RRR 94

6.4.3 Contact resistances 94

6.4.4 Effect of Indium heating 96

6.4.5 Splice resistance 97

6.5 Resistance calculation 98

6.5.1 Introduction 98

6.5.2 Splice resistance 99

6.5.3 Contact resistance 102

6.5.4 Summary 106

6.6 Summary 107

7 HIGH CURRENT PROBES DESIGN

7.1 Introduction 108

7.2 Current leads design 109

7.2.1 Conceptual design 109

7.2.1.1 Shifting guide 110

7.2.1.2 Clamp design 110

7.2.2 Thermal design 111

7.2.2.1 Physic Model 111

7.2.2.2 Current leads optimization 113

7.2.3 Simulations 117

7.2.3.1 LEADX program 117

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7.2.3.2 Flotran analysis 121

7.2.3.3 Flotran results 132

7.3 Sample holders design 132

7.3.1 Introduction 132

7.3.2 Soldered configuration 133

7.3.3 Pressure contact configuration 134

7.4 Instrumentation 135

7.4.1 Temperature sensor 135

7.4.2 He level meter 135

7.4.3 Voltage taps 135

7.5 Summary 135

8 PROBES ASSEMBLY AND COMMISSIONING

8.1 Introduction 137

8.2 Assembly and commissioning of probe and soldered contact holder 138

8.2.1 Assembly 138

8.2.2 Commissioning 141

8.3 Optimization of probe and assembly and commissioning

of pressure contact holder 146

8.3.1 Current lead optimization 146

8.3.1.1 Current leads copper RRR 146

8.3.1.2 Lock model results 147

8.3.1.3 Modification of the current lead profile 147

8.3.1.4 Drilled current leads 150

8.3.2 Pressure contact assembly 151

8.3.3 Pressure contact high current measurement 152

8.4 Summary 156

9 9.1 Introduction 157

9.2 Sample preparation and measurement procedure 158

9.3 Strand description 158

9.4 Results 160

9.4.1 Original tests 160

9.4.2 Mechanical Stability 162

9.4.3 Effect of temperature, impregnation and RRR 163

9.5 Summary 165

CONCLUSIONS 166

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APPENDIX1: Cu Br In contributions in total resistance 169 APPENDIX2: Copper contribution in total resistance 173

APPENDIX3: Contact resistance 179

APPENDIX4: Current Leads Lock 187

APPENDIX5: Current Lead cross section and Reynolds number 189

APPENDIX6: Flotran log. Files 192

APPENDIX7: Probe Drawings 206

APPENDIX8: RRRCL 238

APPENDIX9: Integral 4.2 a 60K numerical solution with Matematica 239 APPENDIX10: Graphical solution with Matematica 240

APPENDIX11: Weigh 241

APPENDIX12: Holes on CLEXT 246

BIBLIOGRAPHY 249