Relativistic Sheet Electron Beam Research Articles

Theoretical research on branch-guide energy coupler for wide bandwidth terahertz relativistic sheet electron beam TWTs

Branch-guide energy couplers can be used in the terahertz relativistic sheet electron beam traveling wave tubes (THz-RSBTWT) for high and high frequency microwave radiations. To analyze this type of coupler, a new method based on the phase superposition principle was put forward in this paper. A physical model was developed, which is applicable no matter the coupler width is large or small. The general distance relationship between the branches was derived and a rapid design formula was obtained, which can help design energy coupler with arbitrary coupling coefficient.

Generation of powerful narrow-band 75-GHz radiation in a free-electron maser with two-dimensional distributed feedback

A planar generator based on a free-electron maser (FEM generator) is developed employing a relativistic sheet electron beam (0.8 MeV/1 kA/4 μs) formed by an ELMI accelerator. A hybrid two-mirror resonator consisting of a two-dimensional upstream and a one-dimensional downstream Bragg reflectors is used as the electrodynamic system. The use of two-dimensional distributed feedback implemented in the upstream Bragg structure has made it possible to achieve stable well reproducible single mode generation regime with transverse dimensions of the system of ∼25 × 2.5 wavelengths. Experiments carried out at a frequency of 75 GHz have yielded narrow-band radiation with spectrum width of ∼20 MHz in pulses with a duration of ∼100–200 ns and power of 30–50 MW.

Investigation of the diocotron instability of an infinitely wide sheet electron beam by using the macroscopic cold-fluid model theory

This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting walls propagating through a uniform magnetic field by using the macroscopic cold-fluid model theory. Assuming low-frequency perturbations with long axial wavelengths, the eigenvalue equation and the dispersion relation are acquired for a sheet electron beam with sharp boundary profile and uniform density. The results presented in this paper has developed the use of the macroscopic cold-fluid model theory by extending the parameter of the electron cyclotron frequency ωc to a wider usage range, which is restricted to be much larger than the plasma frequency ωp in the previous research work. Theoretical analyses and numerical calculations indicate that the transport of the sheet electron beam will be completely stabilized by augmenting the normalized beam thickness to a conductor gap larger than a threshold λb, which is greatly dependent on the parameter ωc/ωp. The larger ωc/ωp is, the smaller λb will be needed. Moreover, the system parameters, including the wave number kx of the perturbations and the relativistic mass factor γb, will also influence the growth rate of diocotron instability obviously.

Excitation of terahertz plasmons eigenmode of a parallel plane guiding system by an electron beam

Two parallel semiconductor plates, separated by a short distance, support surface plasmon eigenmode with amplitude maxima at the inner surfaces of the plates and minimum at the center. A relativistic sheet electron beam propagating through the space between the planes resonantly excites the surface plasma wave (SPW). The frequency of the driven SPW decreases with the energy of the beam while the growth rate increases. At the beam current ≈168 A the growth rate of 5.93×108 rad/s is achieved at the frequency ≈0.51 THz of SPW for the 5 mm ŷ width and spacing between the two plates of ≈2.83 mm. The growth rate scales as 1/3 root of the electron beam current.

周期会切磁场聚焦强流相对论带状电子束的理论分析和粒子模拟

周期会切磁场聚焦强流相对论带状电子束的理论分析和粒子模拟

Propagation of the intense relativistic sheet electron beam with a quasi-rectangular cross section

The sheet electron beam with a quasi-rectangular cross section has been proposed to carry intense current. Obviously different from the elliptical sheet electron beam with the same high aspect ratio, this kind of beam is almost uniform in thickness, and can be generated by the cold metal cathode. Besides, the uniform thickness leads to uniform beam power in the horizontal direction, implying less modes but better counteraction between the beam and microwave. In addition, the uniform thickness make the width of the propagation system,including the cold cathode, the microwave cavities and the focusing magnets,easily changed. Firstly,the space-charge electric field of the sheet electron beam was analyzed numerically, then the focusing magnets, including the periodic cusped magnets and quadrupole magnets, were designed according to the space-charge electric field for beam matching. To validate the above theoretical analysis, particle-in-cell simulation was performed, which shows that the 300 keV, 3 kA sheet electron beam can be well focused by the 0.163 T periodic cusped magnetic fields with the 0.064 T quadrupole magnetic fields. More than 98% of the total current has been propagated through the distance of 300 mm.

The space-charge limiting current of a sheet relativistic electron beam in a rippled rectangular waveguide

The expression of the space-charge limiting current of a sheet relativistic electron beam propagating in a rippled rectangular waveguide is derived. Using numerical computation, interesting results of the space-charge limiting current are provided. For the same sheet relativistic electron beam, the space-charge limiting current in a rippled rectangular waveguide with an average height of be and a ripple amplitude of h0 is less than that in a smooth-walled rectangular waveguide with a height of be−2h0, and larger than that in a smooth-walled rectangular waveguide of a height of be+2h0, and increases as the ripple period decreases. In addition, the larger the ripple amplitude of the rectangular waveguide is, the more rapidly the space-charge limiting current increases with the decrease in the ripple period. These results should be of interest to the area of propagation of intense sheet relativistic electron beam in a rippled rectangular waveguide for application of generating high-power microwaves.

Diffraction selection of modes in planar backward-wave oscillators

We study the possibility of obtaining spatially coherent radiation in a planar backward-wave oscillator fed with a wide sheet electron beam by using natural diffraction divergence of the radiation. This method is efficient for Fresnel parameters being approximately equal to unity. To solve the two-dimensional boundary problem, the spatio-temporal approach is used, which allows one to determine both the self-excitation conditions and the parameters of the stationary generation regime and the boundaries of its stability. The developed theory is used to evaluate the possibility of achieving diffraction synchronization of the radiation in a high-power planar backward-wave oscillator operated in the 8-mm wavelength band and based on a sheet relativistic electron beam produced by the U-3 accelerator of the Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia.

Free electron laser based on the Smith — Purcell radiation

A Smith-Purcell (SP) 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 the coherent radiation with an output peak power up to 50 MW at millimeter wavelengths can be generated by using relativistic electron beam of moderate energy

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.

Modeling of a planar FEL amplifier with a sheet relativistic electron beam

The paper is devoted to the modeling of a 75 GHz planar FEL-amplifier. This amplifier is driven by a sheet electron beam (1 MeV, 2 kA) produced by the U-3 accelerator (BINP). Different approaches based on non-averaged self-consistent system of equations as well as the averaged equations were used for the description of interaction between the electron beam and the TEM-mode of the planar waveguide. Both methods demonstrated similar results with maximum gains 24–25 db, corresponding to an output power of about 250–300 MW and an efficiency of 14–17%. The 2-D version of the PIC-code KARAT was used for additional modeling. KARAT-based simulations demonstrated a maximum gain up to 22 db, output power 160–170 MW and an efficiency of 9%. The reduction of gain can be explained by the space-charge effects.

A novel Smith-Purcell free electron laser

An experiment on a novel Smith–Purcell free electron laser (FEL) is described in this paper. The FEL is driven by a relativistic sheet electron beam of middle energy. The high frequency system of the device is a quasi-optical resonator composed of a diffraction grating and a three-mirror reflector. Coherent radiation with a peak power of tens of kW at the 3 mm waveband is sucessfully detected from an experimental facility. The main experimental parameters are: sheet beam energy from 400 kV to 500 kV; pulse length of voltage 70 ns; pulse beam current 0.2 kA; synchronous guide magnetic field up to 1.2 T with 10 ms pulse length; and grating period 2.2 mm.

Possible use of two-dimensional Bragg structures in an FEL amplifier powered by a sheet electron beam

It is shown that two-dimensional doubly-periodic Bragg structures can be used effectively in the amplification schemes of free electron lasers powered by sheet relativistic electron beams. The presence of such a structure ensures spatial coherence of radiation from different parts of the electron beam when the input signal propagates across the electron flux. Theoretical analysis shows that the gain in the regenerative scheme can reach 50 dB.

Sheet beam emittance measurements by slit-pinhole method

Abstract A method for measuring sheet electron beam emittance is developed. The effective emittances are obtained through construction of particle distribution in the transverse dimensions using slit-pinhole parameters. Measurement of a mild relativistic sheet electron beam is given as an illustration. The modified slit-pinhole method provides a simple means for characterizing sheet electron beam quality.

Diocotron instability of a relativistic sheet electron beam propagating through a rectangular conducting wall

Properties of the diocotron instability in a relativistic sheet electron beam propagating through a rectangular conducting wall are investigated within the framework of a macroscopic cold fluid model. The electron beam is assumed to be partially neutralized by the positive immobile ions with the fractional charge neutralization f. The eigenvalue equation is obtained for low-frequency perturbations in standing waves. The dispersion relation of the diocotron instability is derived and used to investigate stability properties for a broad range of system parameters including the ratio a/d of the beam thickness (2a) to the conductor gap (2d) and the charge neutralization f. The dispersion relation indicates that the system is stabilized by increasing the neutralization f to 1/γ2b, where γb is the characteristic value of the beam relativistic factor. It is also shown that the diocotron perturbations are completely stabilized by increasing the beam thickness to more than one-half the conductor gap (i.e., a/d≳0.5) for f=0. The growth rate of instability is a substantial fraction of the diocotron frequency if the system is unstable.

Langmuir wave excitation by a sheet relativistic electron beam in a homogeneous magnetized plasma

The radiation relaxation of a sheet relativistic electron beam in a homogeneous magnetized palsma is investigated. It is shown that a growing quasi-surface radiating mode is excited in the linear stage of interaction. In the nonlinear state, the wave-electron synchronism is conserved due to automatic matching of the wave propagation angle, which results in a high effieciency (above 80%) of the energy conversion.

SUPER-POWER FREE ELECTRON LASERS WITH TWO-DIMENSIONAL DISTRIBUTED FEEDBACK

To realize spatially coherent radiation from a sheet relativistic electron beams with transverse dimensions essentially exceeding the wavelength, we propose the use of two-dimensional distributed feedback. This feedback can be provided in a Bragg resonator formed by two double-periodic corrugating metal plates, when additional transverse electromagnetic energy fluxes that synchronize the radiation of individual parts of the electron beam take place. It is found that eigenmodes of a 2-D Bragg resonator and proved its high selectivity. Numerical simulation of excitation of a 2-D Bragg resonator by sheet relativistic electron beam and oscillation build-up demonstrates the possibility to provide spatially coherent radiation to a beam of width 102 – 103 wavelengths. The concept of superpower FEL (P ≃ 20 GW ) in the millimeter wave range is discussed.

Experimental and numerical studies of sheet electron beam propagation through a planar wiggler magnet

Detailed experimental studies on sheet relativistic electron beam propagation through a long planar wiggler are reported and compared with numerical simulations. The planar wiggler has 56 periods with a period of 9.6 mm. Typically, the wiggler field peak amplitude is 5 kG. The experimental efforts are focused on controlling the deviation of the beam toward the side edge of the planar wiggler along the wide transverse direction. It is found that a suitably tapered magnetic field configuration at the wiggler entrance can considerably reduce the rate of deviation. The effects of the following techniques on beam transport efficiency are discussed: side focusing, beam transverse velocity tuning at the wiggler entrance, and beam spread limiting. High beam transport efficiency (almost 100%) of a 15-A beam is obtained in some cases. >

High-order mode domination in the instability spectrum of relativistic electron beam in a dielectric-filled waveguide

An instability of the sheet relativistic electron beam (REB) in the planar waveguide, partially filled with a dielectric, is investigated. The dispersion equation is derived and analyzed for a monoenergetic magnetized beam. It is shown that under certain conditions a high-order mode may become dominant in the instability spectrum.

Numerical analysis of radiation by a relativistic electron beam propagating parallel to a reflection grating

Two-dimensional radiation by a relativistic sheet electron beam propagating parallel to a reflection grating composed of a sinusoidally corrugated conducting surface is studied rigorously using the mode-matching method. Accurate dispersion curves for the eigenmodes that govern the Smith-Purcell radiation and the instability of the electromagnetic surface wave are presented. The imaginary parts of the eigenwavenumber and eigenfrequency give the leakage coefficient of space-charge waves and the growth rate of electromagnetic surface waves. Their dependences on the dimensions of the radiating structure are discussed. Optimum parameters for achieving the maximum leakage coefficient and the growth rate are determined. The method is general and can be applied to any two-dimensional system of electron beam coupled to an open periodic structure of arbitrary profile.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>