This article reviews the state-of-the-art in high-power microwave source research. It begins with a discussion of the concepts involved in coherent microwave generation. The main varieties of microwave tubes are classified into three groups, according to the fundamental radiation mechanism involved: Cherenkov, transition, or bremsstrahlung radiation. This is followed by a brief discussion of some of the technical fundamentals of high-power microwave sources, including power supplies and electron guns. Finally, the history and recent developments of both high-peak power and high-average power sources are reviewed in the context of four main areas of application: (1) plasma resonance heating and current drive; (2) rf acceleration of charged particles; (3) radar and communications systems; and (4) high-peak power sources for weapons-effect simulation and exploratory development.

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Review of high-power microwave source research

The physics of modulation of an intense relativistic electron beam by an external microwave source is studied in this paper via experiment, theory, and simulation. It is found that the self‐fields of the electron beam, in general, intensify the current modulation produced by the external source. The linear and nonlinear theory, together with the simulation, show that the classical klystron description in the drift tube region is substantially modified by the beam’s high density. In the modulating gap, electron bunches may be generated instantaneously without the necessity of propagating the beam through a long drift tube. These properties, which have no counterparts in low‐density beams, lead to the generation of large amplitude, coherent, and monochromatic current modulation on an intense beam. The excellent amplitude stability and the phase‐locking characteristics (<2°) of the modulated current, demonstrated in experiments, open new areas of research in high‐power microwave generation and compact partic...

Externally modulated intense relativistic electron beams

The stationary Vlasov-Poisson boundary value problem in a spatially one-dimensional domain is studied The equations describe the flow of electrons in a plane diode Existence is proved when the boundary condition (the cathode emission distribution) is a bounded function which decays super-linearly or a Dirac mass Uniqueness is proved for (physically realistic) boundary conditions which are decreasing functions of the velocity variable It is shown that uniqueness does not always hold for the Dirac mass boundary conditions

A boundary-value problem for the stationary vlasov-poisson equations: The plane diode

This article addresses the new development of high‐power rf klystronlike amplifiers using modulated intense relativistic electron beams. Development of these amplifiers follows earlier research in which the interaction between a high‐impedance (120‐Ω) intense relativistic electron beam and a low‐power rf pulse resulted in the generation of coherent bunches of electrons with excellent amplitude and phase stabilities. In the present experiment a low‐impedance (30‐Ω) large‐diameter (13.2‐cm) annular electron beam of power ∼8 GW was modulated using an external rf source (magnetron at 1.3 GHz) of 0.5 MW power. The interaction of the modulated electron beam with a structure generated a 3‐GW rf pulse that was radiated into the atmosphere. The self‐fields of the intense beam provided significant electrostatic insulation against vacuum breakdown at the modulating gaps and at the rf extraction gap.

Efficient generation of multigigawatt rf power by a klystronlike amplifier

An overview is provided for the novel relativistic klystron amplifiers which are under active study at the Naval Research Laboratory. These amplifiers are driven by an annular intense relativistic electron beam (500-kV, 10-kA range), which is modulated by an external RF source (1.3-GHz, 100-kW range). Experiments, theory, simulation, and simple models are presented to illustrate the unusual properties of such devices which result from the intense space charge of the beam. Chief among them are electrostatic insulation against vacuum breakdown at high power levels, efficient current modulation, short bunching length, and amplitude and phase stability of the output signal. Many of these unexpected features were revealed in two separate experiments: one with a lower current beam (5 kA, 2-cm beam radius), and the other one with a higher current beam (16 kA, 6.6-cm beam radius). Three gigawatts of RF power at 1.3 GHz were generated with the large diameter beam at an efficiency of 35% with 37-dB gain. These experiments are reviewed, along with a combination of particle simulation results and analytic models which facilitate the interpretation. Special attention is paid to the unfamiliar features of these amplifiers, and the critical problems which must be solved before such amplifiers can fulfil their potential in a wide range of applications are addressed. >

Relativistic Klystron amplifiers driven by modulated intense relativistic electron beams

High levels of coherent current and energy oscillations appeared on an intense relativistic electron beam traversing a smooth drift tube in which two or more coaxial cavities were inserted. The frequency of oscillation depended strongly on the geometry of the drift region but only weakly on beam current and voltage. The frequency spectrum of modulation was monochromatic. By changing geometry, frequencies of up to 3 GHz were observed. Relativistic electron beams with voltages varying from 0.25 to 1 MeV and currents from 1 to 8 kA were modulated with efficiencies approaching 100%. The structure of the electron bunches was tailored by changes in the geometry. Both theory and particle simulation show that the presence of the cavities along the drift tube altered the simple streaming motion of the beam in a smooth drift tube resulting in a highly nonlinear beam behavior. The complex beam dynamics was governed by formation of virtual cathodes, reflexing electrons, and autoacceleration. Shaped electron bunches have many applications in collective acceleration, high power microwave production, and plasma heating.

Self-modulation of an intense relativistic electron beam

Recent advances in the physics and technology of the modulated intense relativistic electron beams (IREB's) are reviewed in this paper. Bunched dense electron beams can be used to construct high-power RF sources, which may critically affect future progress in fusion technology. In this paper a system is described in which electrical energy can be converted from a single pulse of relatively long duration into a series of subpulses of short duration (nanosecond and subnanosecond) and of high power (~1010 W). This electrical system consists of an IREB propagating through passive structures. The mutual interaction between the electron beam and one passive structure modifies the IREB so that power compression and beam modulation occur. When the modified IREB interacts with the next passive structure, the kinetic energy of the electrons is converted into electrical energy or RF energy. The beam current modulation depends on the injected IREB and the structure parameters. A 100-percent modulation of the current has been achieved. A single-beam source may be used for exciting radiation in a frequency range of 60 MHz to 10 GHz. In the frequency range of 60-750 MHz a modulated beam with power ~1010 W has already been achieved. IREB modulation at a frequency of ~3 GHz was performed and RF energy was extracted from the bunched beam with power output of 5 × 108 W.

High-Power Modulated Intense Relativistic Electron Sources with Applications to RF Generation and Controlled Thermonuclear Fusion

High levels of current and energy fluctuation appeared on an intense electron beam traversing a smooth drift tube in which two or more wall perturbations were inserted. The frequency of the fluctuations depended strongly on the geometry of the drift region. Theory and particle simulation showed that wall perturbations drastically altered the motion of the beam causing strong coherent current modulation.

Propagation of intense relativistic electron beams through drift tubes with perturbed walls

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Self-modulation of an intense relativistic electron beam

High-Power Modulated Intense Relativistic Electron Sources with Applications to RF Generation and Controlled Thermonuclear Fusion

Propagation of intense relativistic electron beams through drift tubes with perturbed walls