The use of magnets made of high temperature superconductors (HTS) such as BSCCO and REBCO easily provide higher magnetic fields and higher operating temperatures, enabling dramatic improvements in superconducting magnet technology. The LTS magnet technology is very well summarized in text books written by M. N. Wilson (Superconducting magnets, Clarendon Press Oxford, 1983) and Y. Iwasa (Case studies in superconducting magnets, 2nd edition, Springer, 2009), covering such topics as stability, protection, ac loss and so forth. To the contrary, HTS conductors were commercialized only recently and therefore the magnet technology for HTS conductors remains undeveloped, especially so in the case of REBCO conductors. The technological problems for HTS coils thus far encountered are 1) an enormous effect of a screening current-induced magnetic field, 2) degradation in the coil performance due to excessive mechanical stresses applied along the longitudinal and transverse direction, and 3) the difficulty in protecting the magnet in the case of an abrupt thermal runaway. This paper reviews recent progress in overcoming these technological problems for HTS magnets. Both BSCCO and REBCO conductors have been used for HTS magnets in areas such as high field facilities, NMR, MRI, magnetic levitation trains and so forth. The effect of the screening current is the major problem for NMR, MRI, and accelerators, as it substantially distorts spatial field homogeneity and temporal field stability; on the other hand, degradation due to excessive stresses is substantial for high field magnets. Additionally, coil protection is a common and substantive problem among high current density HTS magnets in general. World-wide activities in developing BSCCO and REBCO magnets are overviewed in this paper.

Recent Developments in High-Temperature Superconducting Magnet Technology (Review)

A review of non-traditional approaches and emerging trends in superconducting magnets for MRI is presented. Novel technologies and concepts have arisen in response to new clinical imaging needs, changes in market cost structure, and the realities of newly developing markets. Among key trends are an increasing emphasis on patient comfort and the need for ?greener? magnets with reduced helium usage. The paper starts with a brief overview of the well-optimized conventional MR magnet technology that presently firmly occupies the dominant position in the imaging market up to 9.4?T. Non-traditional magnet geometries, with an emphasis on openness, are reviewed. The prospects of MgB2 and high-temperature superconductors for MRI applications are discussed. In many cases the introduction of novel technologies into a cost-conscious commercial market will be stimulated by growing needs for advanced customized procedures, and specialty scanners such as orthopedic or head imagers can lead the way due to the intrinsic advantages in their design. A review of ultrahigh-field MR is presented, including the largest 11.7?T Iseult magnet. Advanced cryogenics approaches with an emphasis on low-volume helium systems, including hermetically sealed self-contained cryostats requiring no user intervention, as well as future non-traditional non-helium cryogenics, are presented.

Novel technologies and configurations of superconducting magnets for MRI

RASMES (Research Association of Superconducting Magnetic Energy Storage) in Japan developed a road map of SMES for fluctuating electric power compensation of renewable energy systems. Based on the progress of large superconducting coils, the technical status is already established to develop the several MWh class SMES for frequency control, load fluctuation compensation, and generation fluctuation compensation. With integrated operations of several dispersed SMES systems, it is expected that the 100 MWh class SMES for load fluctuation leveling (peak cut) can be introduced in the period of 2020-30, and the first 1 GWh class SMES for daily load leveling can be installed in the period of 2030-40. From the results of Japanese national projects, experimental device developments and SMES design studies, if the output power of SMES is 100 MW, the target cost of SMES can be evaluated with 2000 USD/kW of the unit cost per output power (the unit cost per kW).

Technical and Cost Evaluation on SMES for Electric Power Compensation

Critical current measurements: A compendium of experimental results

This paper develops and summarizes analytical techniques for calculating radially dependent stress and strain in superconducting windings having anisotropic mechanical and thermal properties. The analysis considers stresses due to fabrication procedures, cooldown to helium temperature, and magnetic forces. Representative calculations for a particular superconducting coil are presented.

Stresses in superconducting solenoids

1. Methods of Magnetic Field Generation.- 1.1 High Magnetic Field Laboratories.- 1.2 Conventional Continuous Duty Magnets with and without Iron.- 1.3 Pulsed Magnets.- 1.4 Cryogenic Magnets.- 1.5 Superconducting Coils.- References.- 2. Magnetic Field Calculations.- 2.1 Magnets without Ferromagnetic Yokes.- 2.1.1 Magnetic Fields due to Current Elements.- 2.1.2 Fields due to Filamentary Current Lines.- 2.1.3 Field Corrections.- 2.1.4 Applications.- 2.1.4.1 Circular Current Filament.- 2.1.4.2 Elliptical Conductor.- 2.1.4.3 Dipole Field.- 2.1.4.4 Quadrupole Field.- 2.1.5 Magnetic Field Calculation by Means of Current Sheets.- 2.1.6 Magnetic Field of Cylindrical Coils.- 2.1.6.1 Use of Spherical Harmonics, Axially-Symmetric Coils.- 2.1.7 Magnetic Field of Non-Cylindrical Coils.- 2.1.8 Fields Produced by Means of Distributed Parallel Conductors.- 2.1.8.1 Multipole Coils with Circular Aperture.- 2.1.9 Multipole Coils with Rectangular Aperture.- 2.2 Magnetic Fields due to Coils in Proximity to Ferromagnetic-Materials.- 2.2.1 Introduction.- 2.2.2 Direct Current Magnetization Curves.- 2.2.3 Difference Equations.- 2.2.4 The Grid System.- 2.2.5 Field Intensity in Rectangular Coordinates.- 2.2.6 Finite Difference Equations in Cylindrical Coordinates.- 2.2.7 Field Intensity in Cylindrical Coordinates.- 2.2.8 Field Problem as a Set of Simultaneous Equations.- 2.2.9 Boundaries with Different Permeabilities.- 2.2.10 Right-Angle Boundary with Different Permeabilities on Each Side.- 2.2.11 Curved Boundaries.- 2.2.12 General Boundary Condition.- 2.2.13 Solution of Difference Equations.- 2.2.14 Concept of Residuals.- 2.2.15 A Computational Method.- 2.2.16 The Iron-Air Interface.- 2.2.17 Examples and Results of Numerical Computations.- 2.2.17.1 Superconducting Dipole Magnets.- 2.2.17.2 Superconducting Quadrupole Magnet.- 2.2.17.3 Axially-Symmetric Magnets.- 2.2.17.4 General.- 2.3 Field Calculation of Iron-Bound Air-Core Magnets.- 2.3.1 Current Sheet.- 2.3.2 Coils of Finite Thickness.- 2.3.3 Special Cases.- 2.3.4 The Coil Ampere-Turns.- 2.3.5 The Magnetic Vector Potential.- 2.3.6 The Inner Radius of the Iron Shield.- 2.3.7 Iron Radial Thickness.- 2.3.8 Stored Energy.- 2.3.9 Magnetic Fields due to Axially-Symmetric Iron Distribution.- 2.4 Calculation of Forces.- 2.4.1 Forces due to Coil-Winding.- 2.4.2 Forces due to Thermal Contraction.- 2.4.3 Magnetomechanical Forces Fm.- 2.4.4 Magnetomechanical Forces due to Winding Pretension.- 2.4.5 Magnetomechanical Forces in Cylindrical Geometrics.- 2.4.6 Stresses due to Thermal Contraction.- 2.4.7 Forces for a Dipole Coil Configuration.- 2.4.8 Force Equations for Multipole Coils.- 2.4.9 Forces in Spherical Coils.- 2.4.10 Forces in Toroidal Coils.- 2.5 Calculation of Heating.- References.- 3. Phenomena and Theory of Superconductivity.- 3.1 Theory.- 3.1.1 Introduction.- 3.1.2 Free Electron Theory.- 3.1.3 Zero Field Properties of a BCS Superconductor.- 3.1.4 Superconductors in an Applied Field.- 3.1.5 Type II Superconductors.- 3.1.6 Summary of Free-Electron, BCS and GLAG Formulae.- 3.2 Critical Fields of Type II Superconductors.- 3.2.1 Introduction.- 3.2.2 Magnetostatics and Thermodynamics of Type I Superconductors.- 3.2.3 Intermediate State of Type I Superconductors.- 3.2.4 The Mixed State of Type II Superconductors.- 3.2.5 Exact Theories of the Mixed State.- 3.2.6 Paramagnetic and Impurity Effects on Hc2.- 3.2.7 Critical Fields of intermetallic Compounds.- 3.2.8 Surface Superconductivity.- 3.3 Critical Currents of Type II Superconductors.- 3.3.1 Introduction.- 3.3.2 Forces on Flux Lines.- 3.3.3 Flux Flow.- 3.3.4 Thermally Activated Flux Creep.- 3.3.4.1 Thermally Activated Flux Creep.- 3.3.4.2 Calculation of the Effective Density of Vortex Pinning Sites.- 3.3.4.3 Nature of Vortex Pinning Sites.- 3.3.5 Low Temperature Experimental Results on the Field and Defect Dependence of the Critical Current Density.- 3.3.5.1 High Field Materials.- 3.3.5.2 Low Field Materials.- 3.3.5.3 Other Low Temperature Effects.- 3.3.6 Kim Anderson Theory at Finite Temperatures.- 3.3.7 A.C. Effects.- 3.3.8 Conclusions.- References.- 4. Superconducting Alternating Current Magnets.- 4.1 Alternating Current Losses.- 4.1.1 Introduction.- 4.1.2 Flux Profiles.- 4.1.3 Thin Superconducting Tapes and Filaments.- 4.1.4 Finite Size Slabs and Cylindrical Conductors Located in a Transverse External Field.- 4.1.5 Methods of Calculating Hysteretic Losses due to Alternating Fields.- 4.1.6 Hysteretic Losses in Slabs.- 4.1.7 Application to Multifilamentary Conductors.- 4.1.8 Hysteretic Losses in Cylindrical Shaped Superconductors.- 4.1.9 Hysteretic Losses in Coils Using Hollow Superconducting Filaments.- 4.1.10 Losses in Composites.- 4.1.11 Eddy Current Losses in the Conductor Matrix.- 4.1.12 Self Field Losses.- 4.1.13 Contribution of External Fields.- 4.1.14 Discussion.- 4.1.15 Comparison between Self-Field and Hysteretic Losses.- 4.1.16 Modification of the Hysteretic Losses, if the Transport Current is not Zero.- 4.2 Additional Effects in Twisted Multifilamentary Conductors.- 4.2.1 Axial Diffusion of the Self Field.- 4.2.2 Solution of I (r, z, t).- 4.2.3 Extension of the Self Field Model in Twisted Multi-Filament Conductors.- 4.3 Eddy Current Losses in Metallic Parts.- 4.3.1 Iron Losses in the Flux Return Path.- 4.3.2 Eddy Current Losses in the Metallic Cryostat.- 4.4 Multifilamentary Conductors.- 4.4.1 Cables and Braids.- 4.5 Comparison of Loss-Calculation with Experiments.- 4.6 Methods of Loss Measurement.- 4.6.1 Calorimetric Method.- 4.6.2 Electric Methods.- 4.7 Magnetic and Thermal Instabilities.- 4.7.1 Introduction.- 4.7.2 Diffusion Equations.- 4.7.2.1 Magnetic Diffusivity.- 4.7.2.2 Thermal Diffusivity.- 4.7.3 Stability.- 4.7.3.1 Temperature Rise from Fluxjump.- 4.7.3.2 Adiabatic Stability.- 4.7.3.3 Dynamic Stability.- 4.7.3.4 Steady State Stability.- 4.8 A.C. Magnet Fabrication Techniques.- 4.8.1 Coil Fabrication.- 4.8.2 Electrical-Design.- 4.8.2.1 Current Leads.- 4.8.2.2 Superconductor to Lead Joints.- 4.8.3.1 Transient Voltages in Coils due to Quenches.- 4.9 Irradiation Effects in Superconducting Magnets.- 4.9.1 Introduction.- 4.9.2 Energy Loss by Collisions.- 4.9.3 Irradiation Effects on Type II Superconductors.- 4.9.4 Irradiation Effects on Normal Metals.- 4.9.5 Irradiation Effects on Magnet Insulations and Reinforcements.- 4.9.6 Irradiation Effects on Helium.- References.- 5. Cryogenics.- 5.1 General Properties of Cryogenic Fluids.- 5.1.1 Availability and Production.- 5.2 Low Temperature Processes.- 5.2.1 Handling Cryogenic Fluids.- 5.2.1.1 Safety Precautions.- 5.2.2 Transferring Cryogenic Fluids.- 5.2.3 Liquid Level Measurement.- 5.2.3.1 Introduction.- 5.2.3.2 Methods of Level Measurement.- 5.3 Liquefaction and Refrigeration.- 5.3.1 Basic Principles, Reversible Cycles.- 5.3.2 Efficiency of Real Cycles.- 5.3.3 Non-Isothermal Refrigeration.- 5.3.4 Practical Refrigerators.- 5.3.5 Liquefiers.- 5.3.6 Real Liquefiers.- 5.4 Handling and Storage of Cryogenic Fluids.- 5.5 Physical Properties of Cryogenic Fluids.- 5.5.1 Helium.- 5.5.2 Hydrogen.- 5.5.3 Nitrogen.- 5.6 Physical Properties of Solids.- 5.6.1 Introduction.- 5.6.2 Mechanical Properties of Solids.- 5.6.2.1 Stress-Creep Relation.- 5.6.2.2 Stress-Strain Relation.- 5.6.2.3 Fatigue.- 5.6.3 The Work of Fracture.- 5.6.4 Thermal and Transport Properties of Solids.- 5.7 Heat Losses.- 5.7.1 Heat Conduction.- 5.7.2 Convection.- 5.7.3 Radiation.- 5.7.4 Methods to Minimize Thermal Losses.- 5.7.5 Application.- References.- 6. Economic Consideration in the Design of Water-Cooled, Cryogenic and Superconducting Magnets.- 6.1 Introduction.- 6.2 Cost Comparison for Specific Magnet Systems.- 6.2.1 Solenoids and Split Coils.- 6.2.2 Water-Cooled Solenoids with Uniform Current Density Distribution.- 6.2.3 Cryogenic Magnets with Uniform Current Density Distribution.- 6.2.4 Superconducting Magnets.- 6.2.5 Operating Cost of Superconducting Coils.- 6.2.6 Long Solenoids.- 6.2.7 Magnets for Energy Storage.- 6.2.8 Beam Transport and Accelerator Magnets.- 6.3 Cost Comparison in General.- References.- 7. Examples of Superconducting Magnet Systems.- 7.1 The Argonne National Laboratory 3.7-m Hydrogen Bubble-Chamber Magnet.- 7.2 The CERN Liquid Hydrogen Bubble-Chamber Magnet.- 7.3 Composite Magnet System, the McGill and MIT Hybrid Magnets.- 7.4 The Oak-Ridge -IMP -Superconducting Coil System.- 7.5 The SLAC 7 T, 30-cm Bore, Helmholtz Magnet.- References.

H. Brechna

Papers

Superconducting Magnet Systems