Amplification mechanism of ion-ripple lasers and its possibleapplications

The ion-ripple laser (IRL) is an advanced scheme for generating coherent high-power radiation, in which a relativistic electron beam propagates obliquely through an ion ripple in a plasma. Its amplification mechanism is described by a low gain theory, while the linear growth rate is given by the dispersion relation. The efficiency of the lasing is determined by the nonlinear saturation mechanism discussed. By proper choice of device parameters, sources of microwaves, optical, and perhaps even X-rays can be made. The availability of tunable sources for wide wavelength regimes, coherence and high-power, as well as lower cost and simplicity of equipment, are emphasized     

Feasible Design of a Free Electron Laser Based on the Smith–Parsell Effect

A free electron laser design is considered in which coherent radiation is generated during the flight of a bunched electron beam near a periodic metal target (Smith–Parsell radiation). If the target (array) is placed in a special resonator, optical feedback can be realized. It is proposed to use an array made of thin conductive strips separated with vacuum gaps, since the radiation output in this case is much higher than that attainable with conventional arrays. Varying the array parameters, one can choose the necessary direction and required spectral distribution of the Smith–Parsell radiation. When radiation is generated in the direction normal to the trajectory of the electron beam, the array acts as one of the resonator mirrors.     

High-Power Microwave Generation from a Large-Orbit Gyrotron in Vane and Hole-and-Slot Conducting Wall Geometries

The production of high-power microwave radiation from a large-orbit gyrotron in azimuthally periodic boundary systems is studied theoretically and experimentally. Linear growth rates are calculated for the 2? modes of magnetron-like vane resonator (VR) and hole- and-slot resonator (HASR) systems using a general growth-rate formalism. The experiment involves the interaction of a 2.3-MeV, 1-2-kA, 5-ns rotating electron layer with two different periodic structures. About 500 MW is produced in Ku band with a 20-slot VR system and about 300 MW is produced in X band with a 10-slot HASR system. The relative merits of both types of systems are discussed.     

基于相对论电子束的太赫兹源

太赫兹辐射在基础科学和产业应用中具有重要的应用前景,但传统的电子学和光学方法难以在1～10 THz产生相干的高功率、窄带且连续可调的太赫兹辐射。基于相对论性超短电子束和预调制电子束序列的加速器太赫兹源将能在上述范围内产生可调的高能谱强度窄带太赫兹辐射。综述了清华大学加速器实验室近年来在基于相对论电子束的加速器太赫兹源方面的理论和实验进展,以及与加速器太赫兹源一起发展起来的太赫兹辐射测量、束流诊断和先进加速技术。     

Radiation of a flow of oscillating electrons in the excitation of parametric oscillations

A study is made of phase modulation of an electron flow and the saturation of coherent radiation in such a flow after parametric excitation in a nonlinear system. Expressions are obtained for the intensity of the radiation of a charged particle and the coherent radiation in a resonator. The dependece of the intensity and frequency of the radiation on the amplitude and frequency of the external source are examined. Scientific Research Institute of Nuclear Physics at Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 103–106, October, 1997.     

Observation of stimulated emission at high gyroharmonics: basis for a synchrotron resonance maser

First experimental observations are reported on stimulated coherent synchrotron radiation from highly relativistic electrons in a strong magnetic field. The experiment employed a quasioptical millimeter-wave resonator and a 6-MeV electron beam gyrating in a field of up to 25 kG. Coherent radiation at 54 GHz, corresponding to the 11th gyroharmonic, was observed and characterized. These observations demonstrate the possibility of a synchrotron resonance maser.     

Investigation of a Novel Smith-Purcell Tunable Radiation Source

A novel Smith-Purcell tunable radiation source with relativistic electron beam of middle energy and a quasi-optical resonator composed of diffraction grating and three-mirror reflector is reported. Theoretical analyses and numerical simulation results indicate that coherent radiation with peak power of a few MW order can be achieved from this experimental model. The typical curve of PIC simulation and cool testing experiment is also given.     

Free electron laser operation in the whistler mode

The introduction of a strongly magnetized plasma in the inner region of a free electron laser opens up the possibility of generating coherent radiation in the slow whistler mode using mildly relativistic electron beams. The frequency of emission, however, is limited to below the electron cyclotron frequency. The efficiency of the device can be enhanced by tapering the guide magnetic field     

矩形波导中超短脉冲电子束的相干同步辐射

考虑了当射频调制的超短脉冲电子束径向长度远小于辐射波长时，将其理想化为δ时间函数，提出了用波导本往模展开的方法来计算矩形波导中超短脉冲电子束的相干同步辐射及其频率特性。结果表明：（１）当谐振频率等于调制电子束微脉冲时间隔的射频的整数倍时，辐射模式表现为“纯”的波导本征模。（２）波导效应使得超短脉冲电子束在两个频率处发生相干同步辐射，而且低频支的辐射功率高于高频支的。最后指出波导自由电子激光器单横模     

Coherent X-ray radiation generated by a relativistic electron in an artificial periodic structure

A theory of coherent X-ray radiation from a relativistic electron crossing an artificial periodic layered structure in the Laue scattering geometry is constructed. The expressions describing the spectral-angular radiation parameters are obtained. It is shown that the radiation yield in such a medium may substantially exceed the radiation yield in a crystal under analogous conditions.     

A nonradiative approach to single-mode dielectric resonators

The development of a single-mode dielectric resonator specifically designed for high-frequency paramagnetic resonance applications is discussed. The use of dielectric resonators is expected to give better performances in comparison to metallic cavities, as well established at low frequency. The relatively low dielectric constant of the common good-quality materials at high frequency requires the presence of a metallic shielding in order to obtain an efficient single-mode operation. The configuration proposed in this paper concerns a partially open structure in which the confinement of the radiation is guaranteed by the forbidden propagation around the dielectric region. By this way a single-mode resonator can be obtained for arbitrary values of the employed dielectric constant. The complex resonance frequencies and the field distributions and intensity can then be obtained even in the presence of a lossy sample. An efficient excitation scheme, fully compatible with the common electron paramagnetic resonance setups, has been developed exploiting the nonradiative nature of the proposed device. Preliminary measurements around 90 and 186 GHz have been then successfully realized. Finally, the specific benefits of the proposed resonator have been discussed and compared with the performances of a conventional metallic cavity.     

Coherent X-rays excited by a relativistic electron crossing a periodic stratified structure in Bragg scattering geometry

The dynamic theory of coherent X-rays excited by a relativistic electron crossing an artificial periodic stratified structure in Bragg scattering geometry has been developed for the general case of asymmetric reflection. Expressions describing the spectral-angular characteristics of radiation have been derived and investigated.     

Theory and design of a free-electron maser with two-dimensional feedback driven by a sheet electron beam

The use of two-dimensional Bragg resonators of planar geometry, realizing two-dimensional (2D) distributed feedback, is considered as a method of producing spatially coherent radiation from a large sheet electron beam. The spectrum of eigenmodes is found for a 2D Bragg resonator when the sides of the resonator are open and also when they are closed. The higher selectivity of the open resonator in comparison with the closed one is shown. A time-domain analysis of the excitation of an open 2D Bragg resonator by a sheet electron beam demonstrates that a single-mode steady-state oscillation regime may be obtained for a sheet electron beam of width 100-1000 wavelengths. Nevertheless, for a free-electron maser (FEM) with a closed 2D Bragg resonator, a steady-state regime can also be realized if the beam width does not exceed 50-100 wavelengths. The parameters for a FEM with a 2D planar Bragg resonator driven by a sheet electron beam based on the U-2 accelerator (INP RAS, Novosibirsk) are estimated and the project is described.     

Quantum theory of laser cooling: Statistical description of the process dynamics

A dynamic theory of coherent X-ray radiation generated in a periodic layered medium by a relativistic electron multiply scattered by target atoms has been developed. The expressions describing the spectral–angular characteristics of parametric X-ray radiation and diffracted transition radiation are derived. Numerical calculations based on the derived expressions have been performed.     

Ultra-high order harmonic generation via a free electron laser mechanism

In this paper,by using the"frequency up-conversion"principle with a high gain harmonic generation free electron laser and an external seed laser,we consider the possibility of modulating a relativistic electron beam on the attosecond scale,so that it can produce coherent spontaneous radiation from the deep ultraviolet to the hard X-ray spectral region with a very short radiator.Analytical estimation and three-dimensional numerical modeling show the great potential to reach ultra-high harmonics up to several thousand.For an electron bunch with the typical quality as in the free electron laser scheme and a seed laser with 800 nm wavelength,0.8 nm attosecond trains with alterable duration and GW scale peak power are modeled.The output radiation exhibits good shot-to-shot stability,full coherence and perfect tuning ability between the discrete harmonics of the seed frequency.     

Relativistic ponderomotive forces in the field of intense laser radiation

The motion of a relativistic charged particle in the presence of the field of high-power laser radiation represented in the form of a Gaussian beam of arbitrary mode is analyzed. The vector potential of the radiation field is expanded in terms of a small parameter (the ratio of the wavelength to the Gaussian beam waist). A specific feature of averaging with respect to the phases of the high-mode Gaussian beams is demonstrated. The averaged equations for the motion of particle and a general expression for the ponderomotive relativistic force for the circularly polarized radiation are derived. It is demonstrated that relativistic effects suppress the averaged action of high-power laser radiation on the particle.     

Free electron laser based on the Smith–Purcell radiation

A Smith–Purcell (S–P) free electron laser (FEL) composed of a metallic diffraction flat grating, an open cylindrical mirror cavity and a relativistic sheet electron beam with moderate energy, is presented. The characteristics of this device are studied by theoretical analysis, experimental measurements and particle-in-cell (PIC) simulation method. Results indicate that coherent radiation with output peak power up to 50 MW at millimeter wavelengths can be generated by using relativistic electron beam of moderate energy.     

Powerful Cherenkov oscillators with 2D distributed feedback

The feasibility of using 2D distributed feedback based on 2D planar and coaxial Bragg structures for generating spatially coherent radiation from rectilinear ribbon and tubular electron beams is studied. One-section and sectional Cherenkov masers are analyzed. In the former design, a 2D Bragg structure acts as a resonator and a periodic slow-wave system simultaneously. In the latter (sectional) design, radiation is synchronized in a 2D Bragg structure that is placed at the cathode end of the interaction space and couples longitudinal and transverse (azimuthal) wave flows. The wave is amplified by the electron beam mainly in the fairly long middle section. The output (collector) part contains a standard 1D Bragg structure that partially reflects the amplified radiation toward the cathode and closes the feedback circuit. It is shown that dissipation introduced into the 2D Bragg structure of the sectional design makes it possible to increase one of the transverse sizes of the system to ∼10³ wavelengths with the energy exchange efficiency and one-frequency masing mode stability remaining the same. With such an overdimension, the millimeter-wave radiation integral power may reach a gigawatt level.     

The Turbutron

The physics of the turbutron is reviewed. This newly proposed high-power millimeter-wave source consists of an intensely oscillating relativistic turbulent electron plasma created in and beyond the gap of a diode configuration. The diode consists of an explosive cathode emitter and an extended anode structure connected to the inner and outer conductors, respectively, of a high-voltage pulse line under conditions of space-charge saturation. The gap spacing determines the dominant mode of the turbulent longitudinal waves which are directly converted into free transverse waves polarized parallel to the electron beam. The applied voltage waveform, cathode diameter, total scalar potential, nonlinear bunching mechanisms, and virtual-cathode dynamics determine the complex spectral characteristics. For a turbutron with a megavolt pulse across a 3-mm gap and without a resonator, calculations predict the immediate feasibility of gigawatt power levels at 35 GHz.