Summary) The abstract should follow the structure of the article (relevance, degree of exploration of the problem, the goal, the main results, conclusion) and characterize the theoretical and practical significance of the study results. The abstract should not contain wording echoing the title, cumbersome grammatical structures and abbreviations. The text should be written in scientific style. The volume of abstracts (summaries) depends on the content of the article, but should not be less than 250 words. All abbreviations must be disclosed in the summary (in spite of the fact that they will be disclosed in the main text of the article), references to the numbers of publications from reference list should not be made. The sentences of the abstract should constitute an integral text, which can be made by use of the words “consequently”, “for example”, “as a result”. Avoid the use of unnecessary introductory phrases (eg, “the author of the article considers...”, “The article presents...” and so on.)

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Ministry of Education and Science of the Russian Federation

Collective instabilities and high-gain regime in a free electron laser

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

With intensities 108–1010 times greater than other laboratory sources, X-ray free-electron lasers are currently opening up new frontiers across many areas of science. In this Review we describe how these unconventional lasers work, discuss the range of new sources being developed worldwide, and consider how such X-ray sources may develop over the coming years.

X-ray free-electron lasers

The electron cyclotron maser (ECM) is based on a stimulated cyclotron emission process involving energetic electrons in gyrational motion. It constitutes a cornerstone of relativistic electronics, a discipline that has emerged from our understanding and utilization of relativistic effects for the generation of coherent radiation from free electrons. Over a span of four decades, the ECM has undergone a remarkably successful evolution from basic research to device implementation while continuously being enriched by new physical insights. By delivering unprecedented power levels, ECM-based devices have occupied a unique position in the millimeter and submillimeter regions of the electromagnetic spectrum, and find use in numerous applications such as fusion plasma heating, advanced radars, industrial processing, materials characterization, particle acceleration, and tracking of space objects. This article presents a comprehensive review of the fundamental principles of the ECM and their embodiment in practical devices.

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The electron cyclotron maser

Electron Cyclotron Maser

An exact solution is given for the canonical model equations describing the electromagnetic fields on a free-electron-laser amplifier comprised of a high-quality relativistic electron beam propagating along the axis of a helical pump magnetic field. The case of a cold beam is analyzed in detail and it is shown that, depending upon the parameters, one can have gain when the system is stable, owing to constructive spatial interference of modes, or exponential gain when it is unstable. Gain curves, line shapes, and linewidths are presented for conditions of reported and planned experiments. Reasonable agreement is found with the reported experiments.

Amplification on a relativistic electron beam in a spatially periodic transverse magnetic field

Gain was measured for fast and slow waves propagating in a dielectric-loaded T${\mathrm{E}}_{01}$ axi-symmetric waveguide penetrated by an annular electron beam. This measurement is the first reported in the slow-wave regime, where axial velocity modulation dominates the azimuthal bunching. Small-signal gain at 6.0 GHz of over 30 dB, instantaneous bandwidth of 3.7%, and tuning bandwidth of over 11% are reported. In a feedback-amplifier configuration gain of 53 dB, power output of 20 kW, and 10% electronic efficiency are also reported.

Measurements of Gain for Slow Cyclotron Waves on an Annular Electron Beam

A high-current, high-gradient, high-efficiency, multi-stage cavity cyclotron resonance accelerator (MCCRA) provides energy gains of over 50 MeV/stage, at an acceleration gradient that exceeds 20 MeV/m, in room temperature cavities. The multi-stage cavity cyclotron resonance accelerator includes a charged particle source, a plurality of end-to-end rotating mode room-temperature cavities, and a solenoid coil. The solenoid coil encompasses the cavities and provides a substantially uniform magnetic field that threads through the cavities. Specifically, the MCCRA is provided with a constant magnetic field sufficient to produce a cyclotron frequency a little higher than the RF of the accelerating electric field. A plurality of input feeds, each of which respectively coupled to a cavity, are also provided. According to an embodiment of the invention, the beam from the first cavity passes through a cutoff drift tube and is accelerated further with a cavity supporting a still lower radio-frequency electric field. This embodiment yields a several-milliampere one-gigavolt proton beam efficiently. The single cavity transfers about 70% of the radio-frequency energy to the beam. A multiple-cavity accelerator using a constant or slightly decreasing static magnetic field along its length and using cutoff drift tubes between the cavities operating at progressively lower frequencies, each somewhat lower than the local relativistic cyclotron frequency of the beam in that cavity, provides an extremely-efficient, compact, continuously-operating, medium-energy accelerator. In another embodiment of the invention, the progressively lower frequencies are selected to decrease in substantially equal increments corresponding to a difference frequency. The charged particles are emitted in pulses in correspondence with the difference frequency.

Multi-stage cavity cyclotron resonance accelerators

An electron beam from a cyclotron autoresonant accelerator passing adiabatically along a down-tapered axisymmetric static magnetic field can propagate as an axis-encircling helix. This helix rotates temporally at the fundamental pump frequency of the accelerator, and varies spatially with an axial pitch that depends upon the difference between the pump frequency and the local gyrofrequency. We show that the pitch can thus be freely adjusted so as to allow both frequency and wave-number matching between the beam and a guided fast wave at each harmonic of the pump frequency. As a result, power transfer from beam to wave can occur in a process that is first order in the wave amplitude. Examples of a harmonic converter based on this concept are given for 94- and 1000-GHz sources employing magnetic fields no stronger than 10 kG. Since the electrons can maintain phase coherence during the interaction, one can speculate that the power transfer can be fairly efficient. Practical advantages of this harmonic converter for high-power applications may include alleviation of mode competition, direct output coupling, lower wall heat loading, and simpler beam collectors than for corresponding cavity gyrotron oscillators and noncryogenic magnets.

Jay L. Hirshfield

Papers

Electron Cyclotron Maser

Amplification on a relativistic electron beam in a spatially periodic transverse magnetic field

Measurements of Gain for Slow Cyclotron Waves on an Annular Electron Beam

Multi-stage cavity cyclotron resonance accelerators

Coherent radiation from spatiotemporally modulated gyrating electron beams