High-Magnetic-Field Research and Facilities: [Final Report] (1979)

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1 Introduction High magnetic fields have played a fundamental role in research and technol- ogy. In research, such diverse disciplines as biology, chemistry, engineering, metallurgy, and physics have required the extensive use of magnetic fields. Not only has the phenomenon of magnetism itself been the basis for many fundamental investigations, but it has also led to a rich history of research on and development of magnetic materials and technology. Magnetism continues to be an active and fruitful area for research. In addition, magnetic fields play a central role in many important phenomena and research techniques includ- ing nuclear magnetic resonance (NMR) and electron spin resonance (ESR) measurements, Hall probe and Hall effect measurements, applications to superconductivity, magnetooptic spectroscopy, and tunable semiconductor lasers. A list of research areas involving the use of magnetic fields would be almost endless; however, the Panel's objective is not to provide an exhaustive listing but to give a flavor of the important research needs being fulfilled with the application of magnetic fields. If we turn from research to technology and practical applications, we quickly see here, too, the diverse uses to which magnets have been applied. A partial list includes such varied applications as transformers, motors, gener- ators, audio and video recording, computer technology, radar, television, fu- sion experiments, measuring probes, and mass spectrometers. The application of magnetism to human needs and uses is an unending story, as we continu- ously find new and important usages such as magnetic bubbles for informa- tion storage, linear motors and levitation for moving vehicles, and microwave ovens. Many of these research and technology applications have been achieved with modest fields [up to 1 or 2 tesla (T); 1 T= 104 gauss]. As fields of greater magnitude became available, the utilization of magnetism became more widespread and its applications in research and technology more diverse. A brief comment on the history of the development of magnets is in order. The basic building block of a high-field magnet is a multiturn coil of conduct- 1

2 HIGH-MAGNETIC-FIELD RESEARCH AND FACILITIES ing material containing an electrical current. This nineteenth century inven- tion led to the modern electrical industry through the work of Faraday, Maxwell, and others. Later it was found that the magnetic field generated by the coil could be enhanced by inserting a strongly magnetic material such as iron in the coil. The resulting fields were limited to about 2 T. The first fields above 3 T were achieved with iron-free high-power solenoids as early as 1914. Major advances took place in the 1930's in the United States with Giauque's work on kerosene-cooled solenoids at Berkeley (resulting in 10-T steady-state fields) and Bitter's work on water-cooled solenoids at Massachusetts Institute of Technology (MIT). Bitter's design has endured, and today modifications of it are used in most high-magnetic-field facilities. Magnets of this type are relatively inexpensive (about $20,000); the main capital cost of a facility is the cost of the power supply and cooling system. Hence, most high-field facilities in the world have a number of solenoid magnet stations that can be connected to a large power supply. Magnets of this type now produce fields up to 23 T. In 1911, in a parallel development, Kamerlingh Onnes discovered super- conductivity. For some time it was thought that superconductors could be used as windings for high-field magnets. Unfortunately, these pure metal superconductors become resistive in modest magnetic fields of about 0.1 T. In 1961, Kunzler and his associates found a new class of superconductors (Type II) that remain in the superconducting state even in extremely high fields exceeding 15 T. With this discovery, the avenue for attaining high fields with superconducting coils was opened. Recent rapid advances have led to a substantial number of superconducting magnet systems producing fields greater than 12T (the current world's record is 17.5 T) distributed worldwide. These two technologies, the resistive magnet and the superconducting mag- net, have been joined to produce even higher fields in the range of 25-30 T. Such hybrid magnets afford experimenters the highest dc fields. Still higher magnetic fields have been achieved on a pulsed basis. Quasi- static (up to several tenths of seconds) systems have attained fields of about 40 T. Short-pulse systems provide fields up to 100T, in a nondestructive fashion, for durations up to milliseconds. Fields above 300 T can be gener- ated for microseconds, but coil and sample are destroyed. Fifteen years ago the Francis Bitter National Magnet Laboratory was com- missioned at MIT and was the major facility of its type in the world. Since that time, nearly all high-field technology advances have occurred in the United States. Today major U.S. facilities are located at the National Magnet Laboratory at MIT, the Naval Research Laboratory, the University of Penn- sylvania, and the University of California at Berkeley. Major facilities have also been built all over the world: in France, England, Germany, Holland, Poland, Russia, and Japan.

Introduction 3 The questions we now face are these: How high a magnetic field is it practical to strive for? What are the scientific opportunities in research if we attain higher magnetic fields? What are the technological and developmental opportunities if we have higher magnetic fields? What is the status of the current magnet facilities in the United States? What is the status of current ideas on magnet design for the generation of higher magnetic fields? The objectives of this report are to consider these questions, present per- tinent information, and attempt to arrive at answers. Accordingly, the report is divided into five additional chapters. Chapter 2 contains the conclusions of the Panel and its recommendations. Chapter 3 deals with scientific opportuni- ties for research using high magnetic fields. Chapter 4 treats applications using high magnetic fields. Chapter 5 is concerned with magnet design and materials work related to the generation of high magnetic fields. Last, Chapter 6 re- ports on high-magnetic-field facilities and their use in both the United States and abroad. In part because of the severe time limitation-the interval between initia- tion of the study and its completion being some six months-the Panel did not study a number of important issues. We do not address questions about the funding of the current national facilities, their operational practices, and the caliber of the work performed at them. We did not address questions of whether there should be new national facilities or of where current efforts should be expanded. Where we recommend increased support, we mean either the opening of new facilities or increasing the operation of present facilities or both; we do not make the judgment on which alternative should be chosen. Similarly, we have not considered the possibility of contracting se- lected activities. Although it was suggested that the Panel attempt to handle the zero-based budgeting questions, we did not consider ourselves prepared to do so, nor did we recommend a specific level of funding for those programs that we believe should be expanded or initiated. Further, when we recom- mend work aimed at obtaining higher fields than are now extant, we do not lay out a specific program for achieving this goal.