PLASMAS – LABORATORY AND COSMIC

(Van Nostrand Momentum Book#11). By Prof. Forest I. Boley (Physicsand Astronomy). Princeton, N. J.: D.Van Nostrand Co., Inc., 1966. 154 PP $1.75 (paperbound).

The Commission on College Physics is sponsoring a series of books intended to serve the inquisitive layman as well as the scientist and the engineer. Professor Boley, whose book on plasmas is number eleven in this series, achieves this multiple goal beautifully. With limited use of mathematics, the exposition is nevertheless rigorous and quantitative.

In physics the word "plasma" is used to designate a fourth state of matter, a high temperature gaseous state in which an ap- preciable fraction of the gas atoms is ionized or electrically charged. The number of positive ions is equal to the number of negative electrons so that the gas as a whole is neutral. One could argue that the plasma state is the normal state of matter, since most of the matter in the universe is either sufficiently hot (e.g. the stars) or sufficiently diffuse (e.g. interplanetary and interstellar space) to be highly ionized. In this sense the Earth and the other planets are highly atypical regions where solids, liquids, and ordinary gases predominate. Even on Earth the outer layers of the atmosphere are found in the plasma state, and man-made devices utilizing plasmas are abundant.

Following a description of the general properties of a plasma, the various possible modes of wave propagation are discussed. It is shown that in the absence of a magnetic field, electromagnetic waves can only propagate when the wave frequency is higher than the "plasma frequency," a quantity proportional to the square root of the electron density. When a magnetic field is present, a rich variety of wave modes are possible. Professor Boley shows how the plasma as a conducting fluid clings to the magnetic field lines and how the field lines with the attached fluid behave very much like ordinary strings. When the "strings" are "plucked," so-called Alfven waves travel along the field lines in the same manner that waves travel along a violin string. Since the early experiments on Alfven waves in laboratory plasmas were performed by Proessor Boley and co-workers, his treatment has the ring of authority.

Several recent important experiments with laboratory plasmas are discussed in some detail. The most glamorous of these are the ones motivated by the search for thermonuclear fusion reactors and carried out in devices such as the "astron" and the "stellarator."

The last third of the book is devoted to naturally occurring plasmas. Particular attention is paid to the Sun, the solar wind and the ionosphere. A fascinating discourse on the structure and the evolution of galaxies concludes the discussion.

This book presents an authoritative survey of an important area of modern physics and deserves to be widely read by Dartmouth students, faculty, and alumni.

Associate Professor of Physics