CHAPTER 1

INTRODUCTION

David Larbalestier

THE VISION OF A NEW 21ST CENTURY TECHNOLOGY: POWER APPLICATIONS OF SUPERCONDUCTIVITY

In early 1986, Bednorz and Mueller (1986) made the amazing and unexpected discovery of high temperature superconductivity (HTS) in an entirely new class of layered-perovskite, oxygen-sensitive, copper-oxide ceramics. The new material, (La,Ba)2CaCu4O4-x, had a superconducting transition temperature (Tc) of about 35 K, 50% greater than the best existing low temperature superconductor (LTS) of the time, Nb3Ge, whose Tc is 23 K. This discovery underlies this entire World Technology Evaluation Center (WTEC) study. To exemplify the impact of the discovery, it should be noted that all superconducting technology of the time was based on the use of just two materials, Nb 47 wt.% Ti and Nb3Sn, having Tc values of 9 and 18 K, respectively; thus, their application was directly tied to liquid helium technology, for which the operating temperature range is approximately 2-6 K.

To dramatize the unexpected discovery of HTS, 1986 was also the 75th anniversary of the discovery of superconductivity. The science of superconductivity was doing rather well in 1986. It was 25 years since the 1961 discovery that Nb3Sn could support high critical current density (Jc) at magnetic fields of almost 9 tesla. This 1961 discovery enabled the construction of strong magnetic fields for many purposes. Among these were many types of laboratory magnets, large particle accelerators, and the first truly civilian application of superconductivity, magnetic resonance imaging (MRI). Equally germane for the present WTEC study was the fact that by 1986, the technical feasibility of making many of the components of a power transmission system -- generator, motor, and power cables -- had all been demonstrated using Nb 47 wt.% Ti or Nb3Sn. Economic feasibility was a different issue: For some applications like MRI, particle accelerators, and laboratory magnets, there was no disadvantage to operation at 4-5 K using liquid helium technology, but for others, the commercial outlook was bleak due to the cost and technical obstacles associated with operation at liquid helium temperatures. Nevertheless, the superconductor industry was on a steady growth curve, and on the 75th anniversary there was optimism about the future in the field of superconductivity. This anniversary was celebrated in several ways: Physics Today had a special issue in March 1986 devoted to superconductivity (Tinkham 1986), and the September 1986 Applied Superconductivity Conference had a retrospective honoring the history of the field, paying special attention to the applications (Edelsack 1987). It is ironic that the most concrete prediction of higher Tc was for the compound Nb3Si, whose Tc might possibly reach 30 K (Hughes 1986); unknown to almost all was the submission of the paper on (La,Ba)2CaCu4O4-x that would soon lead to new compounds having Tc greater than 100 K.

By March of 1987, the news that Wu, Chu, and others (Wu 1987) had succeeded in discovering a new member of the class YBa2Cu3O7-[delta] had spread around the world, reaching Fortune, Time, Newsweek, and Japanese comics, to name a very small part of the new public for superconductivity. From this arose a vision of a new superconducting age: where copper or aluminum had been, superconductors would now take over. Superconducting generators would produce electricity, superconducting cables would transmit it, superconducting motors would put the power to use, and superconducting magnetic energy storage units would manage the power quality (Fig. 1.1). Thus, all of the promises demonstrated by LTS devices might actually come to fruition very quickly. The sense of a new age dawning was enhanced by the belief that room temperature superconductivity was just around the corner. Hopes at this time were unconstrained, even by many in the scientific community, for the mechanism of superconductivity in these new compounds was not at all understood. What was clear was that the electron-phonon coupling mechanism responsible for low temperature superconductivity was not capable of giving superconductivity at 100 K, let alone room temperature. The possibilities for high temperature superconductivity seemed limitless.

A decade later, what has become of these dreams? It is clear that a decade is a very short time indeed in which to market basic scientific discoveries, even those such as semiconductors that now exert a massive presence in daily life. The transistor was invented in 1948, but it was the late 1950s before commercial transistors began to enter the electronics market, and the full flowering took another 10-15 years. Today, 10, not 25, years on, superconductors are available with transition temperatures well above liquid nitrogen temperature (77 K) with Tc up to 135 K. Some HTS materials can be made into useful conductors, permitting engineering-scale prototype electrical machines to be demonstrated; however, applications are still dependent on attainment of greater scientific understanding of these very complex materials. Nevertheless, a talented and committed community of researchers, engineers, entrepreneurs, and industrial and government visionaries is working hard throughout the world to bring the vision of the superconducting power economy to fruition. The WTEC panel came back from trips to Japan and Germany convinced that this new economy is a viable 21st century possibility. This report details the basis for this conclusion.


Fig. 1.1. Superconductivity in the electric power system of the future, with widespread use of superconducting generators and motors, fault-current limiters, underground transmission cables, and superconducting magnetic energy storage (Blaugher 1995).



Published: September 1997; WTEC Hyper-Librarian