Joseph V. Minervini, Ph.D.
Both low and high temperature superconductors are usually produced as small round wires or flat tapes with dimensions on the order of 1-12 mm. Although these wires can carry very high currents relative to their cross-sectional area, i.e., very high current density, the absolute value of current they carry may be in the range of some tens to hundreds of amperes, depending on the local magnetic field and temperature. There are many large-scale applications that would be infeasible if conductors were limited to these relatively low value of currents. For example, in the cases of power transmission and power conditioning, high energy and nuclear physics accelerator magnets, or magnets for magnetic confinement fusion, currents in the range of a few kiloamperes to tens of kiloamperes are required. For these applications, the single wires or tapes must be bundled into larger cables to operate at these higher currents. The manufacturing and electrical behaviors of these large cables are much more complex to understand because they introduce issues such as non-uniform current distribution among the wires, and different types of ac losses during magnet ramping or during pulsed or ac operation. The construction of these cables is also usually very different for each type of application and operating conditions. This lecture will introduce you to superconducting cables for these various applications and describe, why they look the way they do, how they perform, and how to manufacture them.
The world scientific community has spent decades developing and refining magnetic confinement fusion theory and experimental devices for the ultimate goal of safely, effectively, and economically generating power from a nuclear fusion reaction. Magnet systems are the ultimate enabling technology for these types of fusion devices. Powerful magnetic fields are required for confinement of the plasma, and, depending on the magnetic configuration, dc and/or pulsed magnetic fields are required for plasma initiation, ohmic heating, inductive current drive, plasma shaping, equilibrium, and stability control. All design concepts for power producing commercial fusion reactors rely on superconducting magnets for efficient and reliable production of these magnetic fields. Future superconducting magnets using high field, high-temperature superconductors (HTS) are now being developed and can significantly enhance the feasibility and practicality of fusion reactors as an energy source. Their application would enable a new generation of compact fusion experiments and power plants, dramatically speeding the development path and improving the overall attractiveness of fusion energy. This talk will describe the present use of superconducting magnets for fusion devices and describe how several, small start-up companies, funded by private investment, are creating the future now by developing high-field, high-temperature superconductors magnets. This will enable a new generation of compact fusion experiments and power plants, dramatically speeding the time for fusion to generate electrical power on the grid and improve the overall attractiveness of fusion energy.