During the past seven years I have been involved in the investigation of high power microwave sources for accelerator and radar applications. As for many others before me, the starting point of this book was a collection of notes on theoretical topics out of the material I had been working on. The notes were the core of a course for graduate students at Cornell University. When I started to prepare these notes it seemed a fairly straight-forward and not very time-consuming task since I had most of the material well organized. Today, three years after the preparation of the first notes, I can only wonder how naive this thought was. Most of my work was oriented towards analytic and quasi-analytic tech niques for the investigation of the interaction of an electron beam with elec tromagnetic waves. These topics are presented in Chaps. 4 and 6. However, for a systematic elaboration of these topics it was necessary to provide some general background, therefore parts of what are today Chaps. 2, 3, and 5 were prepared. Related topics of acceleration concepts were also prepared to some extent but I ran out of time and the material (Chap. 8) was not delivered. In the meantime, various sections of this book were taught at the Technion Israel Institute of Technology and Ben-Gurion University. In the last version I included a discussion on free electron lasers (Chap. 7).

The operation of all conventional traveling wave tubes is fundamentally based on the interaction of an electron beam with the axial RF electric field of a traveling circuit wave; transverse electric fields play only a secondary role in the dynamics. It has long been known, however, that a TWT could be designed to exploit certain advantages inherent in the interaction of an electron beam with a transverse electric circuit wave. In 1960 Siegman [1] published a detailed small signal analysis of the interaction of a filamentary beam with a traveling transverse wave, and found that positive gain could indeed be obtained from this interaction, which produces no longitudinal bunching of the beam. In a transverse interaction, energy is extracted from the axial motion of the beam, as in the longitudinal interaction case, but in such a way that all particles lose the same amount of energy, independent of their location (phase) within an RF period. This result holds strictly speaking only for a filamentary beam. Briggs et.al. [2] were able to estimate the energy spread of a beam of finite radius and to use this estimate to bound the attainable efficiency of a transverse TWT. The Moscow State University group, in collaboration with Istok Corp. and Tory Corp. [3], has been successfully designing, developing, and marketing various types of microwave amplifiers and receiver protectors based on the transverse interaction. As of 2002, however, they were reporting only limited experimental success with transverse TWT's. This may be at least partly due to problems associated with the design and fabrication of a suitable slow wave circuit, which are not simple matters.

A brief description and important conclusions are given on work done at the Electronics Research Laboratory of the University of California for the Wright Air Development Division during the period December 15, 1959, through December 15, 1960. The work includes theoretical and experimental studies on high-temperature plasmas and the containment thereof, electron beams, fast-wave interaction with electron streams, solid-state and electron-beam parametric amplifiers, backward-wave interaction with waves on a ferrite rod or in plasmas, large-signal effects in traveling-wave tubes, and novel fast space-charge wave devices.

Nonlinear Electron-Wave Interaction Phenomena explores the interaction between drifting streams of charged particles and propagating electromagnetic waves. Of particular concern are the situations in which the wave amplitude is large and there is strong coupling between the charged fluid and the wave. Emphasis is placed on those devices that utilize a defined injected stream of some type. Particle and electromagnetic wave velocities both small and comparable to the velocity of light are considered. Comprised of 16 chapters, this book begins with an introduction to the various classes of devices in which the drifting stream (charged fluid) is composed of electrons and/or ions coupled to a slow electromagnetic wave over an extended region. The discussion then turns to Eulerian versus Lagrangian formulation and radio-frequency equivalent circuits, along with space-charge-field expressions. Subsequent chapters focus on the interaction mechanisms in klystrons, traveling-wave amplifiers, and O-type backward-wave oscillators, as well as crossed-field forward- and backward-wave amplifiers, and traveling-wave energy converters. The book also evaluates multibeam and beam-plasma interactions; phase focusing of electron bunches; pre-bunched electron beams; collector depression techniques; and modulation characteristics. This monograph is designed to serve both as a research monograph for workers in the fields of microwave electron and plasma devices and as a text for advanced graduate students.

Experiments with a rotating electron beam waveguide device have been performed. The device used in this investigation has been found to exhibit a strong transverse wave interaction. The interaction takes place at a frequency which is close to the cyclotron frequency of the electron beam. Frequency measurements indicate that the interaction frequency is slightly less than the cyclotron frequency and that the interaction frequency varies inversely with beam voltage. Both gain and oscillation have been observed. The interaction appears to be of a backwardwave nature. The transverse-wave interaction theory indicates that backward-wave but not forward-wave active coupling may occur. The observed values of gain are less than the calculated values but are within an order of magnitude. The interaction is found to be strong at the cutoff frequencies. This is in agreement with the transverse-wave theory. The interaction appears to be greatly influenced by the reflections in the waveguide circuit. The results of this investigation indicate that strong transverse interactions can occur in fast-wave circuits. Succeeding experimental work will require a circuit which has better transmission over a broad frequency range. This could be easily accomplished with a broadband vacuum window. An improved beam launching system is still needed if beam parameter effects are to be more carefully observed. (Author).