Magnetic devices are even more important in the scientific world than they are in everyday life. Instruments that take advantage of magnetic phenomena or that use magnets to produce electromagnetic radiation are used in many fields, the most spectacular being the accelerators employed in high-energy physics to study the structure of subatomic particles. High-field magnets are used to control particle trajectories in accelerators, and over the years, the interest of the high-energy physics community in increasing the energies at which accelerators operate has been a powerful driver of magnet technology.

THE SIGNIFICANCE OF HIGH MAGNETIC FIELD RESEARCH

Most of the magnetic devices important to the public do not generate high fields, MRI being the exception. Thus it is reasonable to ask why the nation should support high magnetic field science and technology. Before this question can be answered, some background information must be supplied. The committee starts by reminding the reader that there are two kinds of magnets: permanent magnets and electromagnets.

Permanent magnets are made of substances like iron (Fe), cobalt (Co), and nickel (Ni), the atoms of which have large magnetic moments. When those substances are in their unmagnetized states, the magnetic moments of their atoms are randomly oriented. Magnetization is achieved by making the magnetic moments of their constituent atoms point in the same direction, which can be done by exposing the substances to an external magnetic field. What distinguishes a magnetizable substance from another substance that contains atoms with magnetic moments is that once the magnetic moments of its atoms have become aligned, they remain that way. Thus, a piece of iron that has been exposed briefly to a magnetic field emerges with a net magnetic moment that persists; it has become a permanent magnet. A compass needle is a permanent magnet, and permanent magnets can produce fields up to about 2 T. Permanent magnets have many practical uses, and the search for magnetizable materials with improved properties is ongoing; its goals include increasing the efficiency of electrical motors and generators.

Electromagnets can be made of any material that conducts electricity, regardless of the magnetic properties of its atoms, and they produce magnetic fields via the Oersted effect whenever an electric current flows through them. Electromagnets are commonly made from coils of an electrical conductor. Since the field contributed by each turn in a coil adds to that of its neighbors, and the field per turn increases with electric current, the more turns in the coil and the greater the current put through it, the stronger the magnetic field that results. All high-field magnets—that is, magnets that generate fields substantially greater than 2 T (the limit of permanent magnetization for iron)—are electromagnets.



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