Article

Method of suppressing feedback oscillations in free electron lasers

January 1990

Authors:

This patent describes a method of suppressing feedback oscillations in a free electron laser having an elongated waveguide, means for providing an electron beam propagating through the waveguide, means for superimposing microwave energy onto the electron beam, and means for providing a wiggler field to provide an interaction region inside the waveguide. It comprises: placing an attenuator in the interaction region inside the waveguide.

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Article

Further Experiments On A Wiggler-focused Sheet Electron Beam Small Period Free Electron Laser Amplif...

January 1994 · IEEE International Conference on Plasma Science

The first operation of a free electron laser amplifier with a small period wiggler and a sheet electron beam has been successfully demonstrated, and up to 15--17 dB gain was achieved at 94 GHz with 56 periods of uniform wiggler at an input RF power level of several Watts. Further studies on this device have been performed at an input microwave power level of {approximately} 1 kw at a frequency of ... [Show full abstract] 85 GHz. Preliminary results of these experiments are presented. Experimental results will be compared with theoretical predictions from a one-dimensional simulation, code. Nonlinear saturation characteristics of this novel free electron laser amplifier will be discussed based on the experimental results. Theoretical analysis and numerical simulations show that a longer uniform wiggler is needed for the free electron laser amplifier to be driven into saturation. For this purpose, another 18 period section of uniform wiggler has been fabricated, which will be attached to the existing 56 period wiggler. Results of wiggler magnetic field measurements and studies of electron beam propagation through this newly fabricated wiggler will also be presented.

Article

Low-gain free-electron laser near cyclotron resonance

June 1982 · Physical review A, Atomic, molecular, and optical physics

The Einstein-coefficient method is used to calculate the growth rate of a low-gain free-electron laser for a tenuous relativistic electron beam propagating in the combined axial and transverse helical wiggler fields B0êz-(δB cosk0zêx+δB sink0zêy). The analysis assumes that the system is close to resonance between the electron-cyclotron frequency in the guide field (ωc=eB0/γmc) and the wiggler ... [Show full abstract] frequency in the beam frame (ω0=k0Vb). It is shown that the gain near resonance can be substantially enhanced relative to the gain obtained in the region far from resonance.

Article

Mode-locked free-electron laser oscillator

July 1992 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment

In this experiment we observe emission of a single RF macropulse from a mode-locked FEL oscillator. The FEL employs a continuous electron beam and operates in the microwave regime. The amplitude mode-locking is achieved by modulating the attenuation of the FEL ring cavity at its round-trip frequency (~ 27 MHz). The observed RF macropulse consists of short RF micropulses. Their period (~ 37 ns) is ... [Show full abstract] determined by the modulating frequency, and their width is comparable to the slippage time (~ 3 ns). Examples of experimental results of amplitude mode-locked FEL signals are presented for coaxial-line and waveguide cavity sections. Department of Nuclear Engineering, Tokyo University, Tokyo 113, Japan.

Article

High-power broadband plasma maser with magnetic self-insulation

January 2018 · Physics of Plasmas

Presented in this paper are the results of a particle-in-cell modelling of a novel high-power microwave (HPM) source which combines the properties of two devices. The first prototype is a magnetically insulated transmission line oscillator (MILO), an HPM self-oscillator which does not need an external magnetic field and irradiates a narrow spectrum depending on its iris-loaded slow-wave ... [Show full abstract] structure. The second prototype is a plasma maser, a Cherenkov HPM amplifier driven by a high-current relativistic electron beam propagating in a strong external magnetic field in plasma which acts as a slow-wave structure. The radiation frequency of plasma masers mainly depends on an easily variable plasma concentration; hence, their spectrum may overlap a few octaves. The plasma-based HPM device described in this paper operates without an external magnetic field: it looks like an MILO in which the iris-loaded slow-wave structure is substituted by a hollow plasma tube. The small pulse duration of ∼1.5 ns prevents a feedback rise in the 20-cm long generation section so that the device operates as a noise amplifier. Unlike conventional ultra wideband generators, the spectrum depends not only on the pulse duration but mainly on plasma, so the operation frequency of the device ranges within 12 GHz. For irradiated frequencies above 2 GHz, the total pulse energy efficiency of 7% is demonstrated at the HPM power level ∼1 GW.

Article

Eigen Modes of a Dielectr ic Loaded Coaxial Plasma Waveguide

January 2005

The theoretical studies of High frequency eigen modes of a dielectric loaded coaxial wave guide in the presence of an annular plasma column is presented. The dispersion equation is derived through the application of the appropriate boundary conditions, which result in an eighth order determinant. In the presence of a dielectric layer on the conducting surfaces, the azimuthally symmetric modes ... [Show full abstract] have been identified as HE, EH, cyclotron, and space charge modes for coaxial wave guide. Introduction: There has been growing interest in the plasma filled cylindrical waveguides in recent years (1-4). A consid erable number of microwave sources employ cylindrical waveguides, containing axis encircling electron beams. In these devices the annular plasma column interacts with the modes of empty waveguides, in which case they have been referred to as large-orbit gyrotrons, or with the azimuthally periodic wiggler magnetic field where they are called circular geometry free electron lasers. In either case, frequencies of the generated electromagnetic-electrostatic waves have been shown to have a strong dependence on the radii of coaxial waveguide and on relative positions of the inner and outer radii of the beam (5). Analysis of the plasma waveguide requires knowledge of its eigen modes. High frequency eigen modes of a magnetized plasma waveguide are characterized in four families, EH and HE waveguide modes, cyclotron modes, and space-charge modes. The governing equations: Consider an annular plasma column with inner radius i R and outer radius o R located inside a dielectric loaded coaxial waveguide is immersed in a uniform static axial magnetic field, Z a B ˆ C. The coaxial waveguide consists of an inner metallic cylinder with outer radius a and an outer metallic cylinder with inner radius b. The cross section of the dielectric loaded coaxial waveguide with an annular plasma column is shown in Figure 1. Fig1. Cross section of dielectric

Article

Study of plasma influence on interaction in the free electron laser with electron beam pumping

May 1992

N.L. Romashin

The operation of free electron laser is considered when it has two electron beams and one of them is the pumping beam. The efficiency of such a laser increases with increasing the beam currents. It is realized easier in the waveguide filled by plasma. The combination interaction of two relativistic beams in smooth waveguide filled by plasma in axial magnetic field is considered. The influence of ... [Show full abstract] plasma on the efficiency of beam interaction is investigated. The increasing of efficiency is achieved in the case of weakly and strongly magnetized plasma at the pumping frequency which is near to the electron plasma frequency.

Article

The Interaction of High-and Low-Frequency Waves in a Free Electron Laser

July 1990 · IEEE Transactions on Plasma Science

When a free electron laser (FEL) interaction occurs inside a waveguide, there are two possible operating frequencies at the two intersections of the beam line with the waveguide dispersion curve. Using a one-dimensional model valid for a low-gain oscillator, the mode competition between the high- and low-frequency waves is studied. It is found that the low-frequency wave can be nonlinearly ... [Show full abstract] suppressed, even when its linear growth rate is positive. When the frequency ratio is two, phase locking occurs and the nonlinear gain of the low-frequency wave can exceed its linear growth rate

Article

Gain enhancement in a two-frequency high-gain waveguide free-electron laser

May 2002 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment

In a waveguide monomode free-electron laser (FEL), two resonant frequencies can be amplified by the electron beam. At the CEA/CESTA facility, single-pass high-gain FEL experiments have been performed over the last five years using relativistic electron beams provided by induction linacs. Most of the work was done in the amplifier regime (at the higher frequency) with the aim of producing a 35GHz ... [Show full abstract] bunched beam. However, super-radiant measurements were also made and have shown that the FEL gain at the upper frequency is higher than in the amplifier regime and may be driven by the lower frequency FEL interaction.

Article

Three-dimensional Raman free electron laser in a waveguide with annular electron beam

June 2003 · Physics of Plasmas

A linear theory for a free electron laser with a three-dimensional helical wiggler and axial magnetic field in the collective regime is presented. The configuration consists of an annular electron beam propagating inside a cylindrical waveguide. Parametric decay of the wiggler pump wave, in the beam frame, into a space-charge wave and an electric-magnetic waveguide mode is analyzed in three ... [Show full abstract] dimensions. A nonlinear wave equation for the three-wave interaction is derived and employed to obtain a formula for the spatial growth rate of the excited eigenmodes. Numerical analysis is conducted to study the growth rate, radiation wavelength, and required relativistic factor as functions of axial magnetic field B0. Variation of growth rate with the beam thickness and the radius of the equilibrium trajectory was also studied.

Article

Experimental studies of a circular-geometry free-electron laser

Aghamir

The generation of microwave radiation in a circular-geometry free-electron laser was studied experimentally. The microwave emission is the result of the interaction of a rotating relativistic electron beam (2 MeV, 1 kA, 5 nsec) with an azimuthally periodic wiggler magnetic field. The rotating electron beam was produced by injecting a hollow nonrotating beam into a narrow magnetic cusp. Radiation ... [Show full abstract] spectral measurements were made for two separate experimental systems. The first series of experiments was performed with a magnet holder structure in which the gap between the inner and outer conductors of the coaxial waveguide was small, thus the effect of the negative mass instability may be ignored. Narrow-band radiation was observed at 88 and 175 GHz for a wiggler field configuration with a period of 6.28 and 3.14 cm, respectively. The second series of experiments concentrated on a wiggler field with a period of 6.28 cm. These experiments were performed with a system in which the effect of the negative mass instability was encouraged by enlarging the gap between the coaxial waveguide conductors. The experimental results are in reasonable agreement with the theoretical expectations.

Article

Full-text available

Mode and gain analysis for symmetric and staggered grating-waveguide free-electron laser

March 2007 · Review of Modern Physics

A grating-waveguide free-electron laser is driven by an axial electron beam that propagates between two planar gratings. This investigation addresses the mode analysis, gain calculation, and frequency tuning for such a device with arbitrary longitudinal and transverse displacements between the two gratings. It demonstrates that a grating waveguide free-electron laser is a promising coherent THz ... [Show full abstract] emitter when it is adopted as a backward-wave oscillator or a distributed-feedback oscillator.

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Conference Paper

Synchronism conditions for a hybrid weakly-relativistic FEL

October 2005

We propose an analytical technique of twofold perturbation expansion to solve the nonlinear equations of motion of weakly-relativistic electrons moving in the magnetostatic pump field of a hybrid planar free electron laser (FEL) and apply it to obtain linear corrections to the electron trajectories caused by interaction with given propagating modes of a circular waveguide. In a single-particle ... [Show full abstract] approximation conditions of the most efficient interaction between an electron beam and propagating modes of a circular waveguide (resonant conditions) are derived analytically using small-signal theory in the microwave field.

Last Updated: 05 Jul 2022

Method of suppressing feedback oscillations in free electron lasers

Abstract

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