Bibliography

V. M. Lopukhin. Excitation of electromagnetic oscillations and waves by electron beams. Gostekhizdat, 1953, 324 pp., price 10 rubles 50 kopecks.

The idea of a unified treatment of physical processes in various ultra-high-frequency generating devices is not new. In one form or another it has been presented in a number of journal articles and monographs published over the last ten years. In the reviewed book this idea is developed most consistently, taking into account all modern methods of ultra-high-frequency generation.

An unquestionable merit of the book is its broad and systematic coverage of works by Soviet scientists, which form the basis of the exposition and determine, to a known extent, the method of treating the phenomena under consideration. In a more or less systematized form the author examines the problem of the interaction of electron beams and high-frequency electric fields, discusses various possible approximations in solving this problem, and indicates the specific physical conditions for which a given approximation is valid. A valuable quality of the monograph is its detailed discussion of the limits of applicability of various approximations, such as the prescribed-field approximation and the prescribed-current approximation.

The consideration of specific devices—the monotron, the two-cavity and reflecting klystrons—has an illustrative character: various methods of solving the general problem are demonstrated on them. The author devotes considerable attention to generation methods in which continuous interaction of the field and the electron beam is used, in particular to various modifications of traveling-wave tubes and electron-wave tubes.

A good impression is made by the clear logic of presentation, the progression from simpler problems to more complex ones, and the introduction in many places of indications of questions requiring further resolution. Many sections of the book are original in content and are based on numerous works carried out by the author or with his participation.

The most important problems in the book are considered by the method of jointly solving the equations of the electromagnetic field and the electron beam. The latter method is a logical consequence of the physical continuity of the interaction of the electromagnetic field and the electron beam in most modern ultra-high-frequency devices. Characteristic examples in this respect are devices of the traveling-wave-tube type, to whose study a considerable part of the book is devoted. From the point of view of the mathematical apparatus employed, it is tempting to extend this method to various types of klystrons, as the author makes extensive use of it. However, in doing so the important circumstance remains in the shadows—

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that there is an essential physical difference between generators of the klystron type and generators with continuous interaction. Moreover, the author’s application to klystron-type devices of the general method, which in its formally mathematical content reflects the physical fact of the continuity of interaction between the field and the stream, creates unnecessary mathematical encumbrances and does not always allow the author to make successful use of the customary physical representations—for example, the representation of the phase focusing of a stream, which the author treats as the “intersection of electron trajectories.” It would undoubtedly have been useful not to pass over in silence the very clear and, at the same time, for many results leading by a considerably simpler route, “electron-kinematic” treatment of such electronic devices as the reflex and two-cavity klystrons.

The author repeatedly speaks of determining the amplitude of self-oscillations with the aid of the expressions he has obtained. It should be emphasized that equations such as (14.11), valid for the case of small amplitudes and small densities of the electron stream, make it possible to determine the oscillation amplitudes only for a linear approximation.

The author strives to conduct the exposition in a very concise language saturated with mathematics. However, he does not everywhere succeed in adhering to a uniform style. The exposition of the greater part of the book gives the impression of hypertrophied mathematicalness, not at the expense of the complexity of the mathematical apparatus employed, but at the expense of an obvious predominance of it over the exposition of the physical essence of the matter. This is expressed, in particular, in the fact that even when explaining one or another derivation the author prefers to use mathematical symbols instead of physical concepts. Against the background of such mathematicalness, apparently arising from a desire to economize the exposition, the author also allows entirely superfluous lengthy passages, setting forth matters known from general courses and at times quite elementary matters, which could have been avoided in a monograph. These include: the detailed derivation of the theorem on induced currents (pp. 45–49), a retelling of elementary information about filters (pp. 136–141), information on eigenfunctions known from the theory of resonators (pp. 97–103). It was hardly necessary to spend four pages of text (289–293) in order to arrive at the trivial conclusion concerning the possibility of focusing electron streams in a TWT with the aid of a longitudinal magnetic field.

At the same time the author does not give proper attention to certain fundamental propositions. Thus, on p. 187 the author for the first time applies the method of “joining” (matching) the fields of the comb space and the interaction space. The possibility of such matching constitutes one of the basic premises of the work, a premise applied in considering all subsequent systems. In this case the “joining” is performed only in a consecutive discrete series of points located in the middle of each cell. This method is very imperfect, and attempts have been made to circumvent it (for example, by choosing a special coordinate system, etc.). The justifications and limits of applicability of this method should have been clarified in greater detail.

Along with the shortcomings noted above, there are also other, comparatively minor defects relating to the method of exposition. The author repeatedly emphasizes the circumstance that the questions he expounds belong to the range of centimeter radio waves, to generators and amplifiers of the centimeter range. Such terminology creates an unnecessary and somewhat formal limitation by range, since the theory and the examples of specific devices set forth in the book can, generally speaking, also be applied in the decimeter and millimeter radio-wave ranges. From this point of view, the term “ultrahigh frequencies” would have been more appropriate,

Bibliography

which has found wide circulation in our literature. The exposition in a number of cases is characterized by a lack of physical clarity. In particular, drawings of systems with periodic boundary conditions are given without pictures of the high-frequency electric field (for example, p. 177), and most of the drawings and diagrams have an overly abstract character of “linear” schemes.

The remarks made above do not alter the overall positive assessment of V. M. Lopukhin’s monograph as a highly valuable and necessary book devoted to the important and topical question of the interaction of electron streams with the electromagnetic fields of oscillatory and guiding ultrahigh-frequency systems. This monograph will undoubtedly be useful to scientific workers and students interested in questions of the generation and amplification of ultrahigh frequencies.

V. Kalinin, G. Gershtein, N. Sovetov