Stabilization of Superconducting Magnetic Systems

I am indeed pleased to prepare this brief foreword for this book, written by several of my friends and colleagues in the Soviet Union. The book was first published in the Russian language in Moscow in 1975. The phenomenon of superconductivity was discovered in 1911 and promised to be important to the production of electromagnets since superconductors would not dissipate Joule heat. Unfortunate­ ly the first materials which were discovered to be superconducting reverted to the normal resistive state in magnetic fields of a few tesla. Thus the development that was hoped for by hundredths of a the early pioneers was destined to be delayed for over half a century. In 1961 the intermetallic compound NbaSn was found to be superconducting in a field of about 200 teslas. This breakthrough marked a turning point, and 50 years after the discovery of superconductivity an intensive period of technological development began. There are many applications of superconductivity that are now being pursued, but perhaps one of the most important is super­ conducting magnetic systems. There was a general feeling in the early 1960s that the intermetallic compounds and alloys that were found to retain superconductivity in the presence of high magnetic fields would make the commercialization of superconducting magnets a relatively simple matter. However, the next few years were ones of disillusionment; large magnets were found to be unstable, causing them to revert to the normal state at much lower magnetic fields than predicted.

I Superconductivity and Its Applications.- 1. The future of superconductivity in modern technology.- 1.1. Introduction.- 1.2. Superconducting magnetic systems.- 2. The nature of superconductivity.- 2.1. General principles.- 2.2. Superconductors of the first and second kinds.- 2.3. Creep and jumps in magnetic flux in nonideal Superconductors of the second kind.- 2.4. Resistive state of nonideal superconductors of the second kind.- 3. Protection of superconducting magnetic systems.- 3.1. General principles.- 3.2. Transformer method.- 3.3. Discharge into an external load.- 3.4. Reasons for the development of a normal zone.- 3.5. Stabilization of superconductors in their various forms.- II Method of Thermal Stabilization.- 4. Equilibrium of the normal zone in combined conductors under isothermal conditions.- 4.1. Stekly model of a stabilized superconductor.- 4.2. Influence of contact thermal resistance at a superconductor—substrate boundary.- 4.3. Influence of the finite thermal conductivity of a superconductor on the stability of combined conductors.- 4.4. Influence of the boiling crisis in liquid helium on the conditions of thermal equilibrium in a combined conductor.- 4.5. Equilibrium of a combined conductor in the normal state.- 4.6. Volt—ampere characteristics of combined conductors.- 4.7. Method of the low-resistance shunt.- 4.8. Experimental results.- 5. Equilibrium of the normal zone in combined conductors in the presence of a longitudinal temperature gradient.- 5.1. General principles.- 5.2. Combined conductor with a longitudinal temperature gradient.- 5.3. Effect of the boiling crisis on the equilibrium conditions.- 5.4. Effect of electrical contact resistance.- 5.5. Stability of a combined conductor for an arbitrary longitudinal temperature distribution.- 5.6. Experimental results.- 6. Propagation of the normal zone in a superconducting coil.- 6.1. Method of studying the propagation of the normal zone.- 6.2. Propagation of the normal zone in a thinly packed coil.- 6.3. Influence of cooling the coil with superfluid helium.- 6.4. Rate of propagation of the normal zone along a combined conductor.- 7. Combined conductors with forced cooling.- 7.1. General principles.- 7.2. Theory of the combined conductor with forced cooling.- 7.3. Conditions of thermal equilibrium of the normal zone.- 8. Equilibrium and propagation of the normal zone in a close-packed superconducting coil.- 8.1. Principal characteristics of close-packed superconducting coils.- 8.2. Experimental results.- 8.3. Transition of a superconducting solenoid into the normal state.- 8.4. Comparison of the parameters of transient processes in close and thinly packed coils.- III Combined Conductors with Internal Stabilization.- 9. Stability of superconductors of the second kind with respect to flux jumps.- 9.1. General principles.- 9.2. Magnetization of nonideal superconductors of the second kind.- 9.3. Stability of the screening currents in a superconductor of the second kind.- 9.4. Criterion of adiabatic stability in the presence of a transport current.- 9.5. Stability of the transport current in relation to finite flux jumps.- 10. Multiple-core straight conductors.- 10.1. Model of a multiple-core straight conductor.- 10.2. Criteria of the adiabatic stability of a straight combined conductor.- 10.3. Criterion of electrodynamic stability for combined conductors.- 11. Twisted and coiled combined conductors.- 11.1. Penetration of a magnetic field into a coiled combined conductor.- 11.2. Distribution of transport current in twisted conductors and the stability of the latter.- 11.3. Plaited (transposed) combined conductors.- 11.4. Combined conductors for obtaining rapidly-varying magnetic fields.- Appendix: Dimensionless volt—ampere characteristics of combined conductors.- References.