Electron Beam Wave Research Articles

Waves in relativistic electron beam in low-density plasma

Waves in electron beam in low-density plasma are analyzed. The analysis is based on complete electrodynamics consideration. Dependencies of dispersion laws from system parameters are investigated. It is shown that when relativistic electron beam is passed through low-density plasma surface waves of two types may exist. The first type is a high frequency wave on a boundary between the beam and neutralization area and the second type wave is on the boundary between neutralization area and stationary plasma.

Design and numerical simulation of a high power capacity relativistic backward wave oscillator with an electron collection cavity

A high power capacity relativistic backward wave oscillator with an electron collection cavity (ECC) placed at the downstream of the slow wave structure (SWS) is presented. The breakdown threshold is increased, and the density of seed electron is suppressed by preventing the secondary electron, plasma, and powder generated from the bombardment of spent electron beam on the surface of the collector drifting to the extractor and beam-wave interaction region. The maximum longitudinal electric field in the device is reduced through extension of the span between electron beam and slow wave structure and weakening the Cerenkov radiation. The conversion efficiency reaches up to 52% owing to enhanced transit time radiation taking place at the entrance of the ECC. The maximum longitudinal electric field is 1.1 MV/cm on the surface of SWSs when the output power is 7.3 GW and the power capacity improves significantly.

High frequency characteristics of dielectric-loaded grating for terahertz Smith-Purcell radiation

The research on a Smith-Purcell device becomes active since it holds promise in developing a high power, tunable, and compact terahertz radiation source. In this paper, a dielectric loaded grating for Smith-Purcell device is proposed. By investigating the interaction between the sheet electron beam and surface wave above the grating, the dispersion equation with electron beam is derived, in which the electron beam has a finite thickness. And then the growth rate of the beam-wave interaction is numerically calculated from the dispersion equation. In addition, the current threshold for oscillators, known as a start current, is carefully estimated from the dispersion equation by considering the boundary conditions of electromagnetic field. The effects of structure length, electron beam parameters and dielectric constant on start current are analyzed at length. The results reveal that the start current decreases as the structure length increases. This is because as the structure length becomes greater, the distance of the beam-wave interaction becomes longer, which can strengthen the beam-wave interaction. And with increasing beam thickness and beam-grating distance, the start current increases. Because the electric field of the surface wave decreases exponentially with the increase of distance from the grating, the electron beam far from the grating cannot be bunched by the field, which makes it harder for Smith-Purcell device to oscillate. However, as the beam voltage becomes greater, the start current decreases first quickly and then slightly. Compared with the case of metal grating, it can be seen that the use of dielectric can improve the growth rate and reduce the start current for the operation of a Smith-Purcell backward wave oscillator. The start current decreases quickly when the dielectric constant is greater than 1. Then it increases slightly when dielectric constant is between 2 and 3, and finally the start current continues to decrease. But it cannot be helpful to choose a very big value of dielectric in order to obtain a low start current, because the operation frequency decreases as dielectric constant increases. It is more appropriate to choose a dielectric constant in a required frequency range. The predictions of our theory and the results from the particle-in-cell simulation are consistent with each other, which verifies the validity and accuracy of the theory in this paper.

The instability in the radially non-uniform electron beam-ion channel system

The instability caused by the interaction among the electron beam, plasma, and electromagnetic (EM) waves in a radially non-uniform ion channel is studied. The dispersion relation of the interaction is derived in this paper. The study shows that the EM instability can be induced nearby the center of the beam through the coupling between the fast plasma wave and forward EM wave. On the other hand, the beam mode instability is found in the region relatively far from the center, which means the beam mode can couple with the slow plasma wave so that the electron beam can provide energy to the plasma wave. The distributions of the instability with radius and plasma density are given, respectively, by the numerical simulation, and the result shows that the instability frequency is increased exponentially with the increase of the plasma density. When the plasma density reaches 1×1024m−3, the scale of the frequency can be 10 THz, which provides a theoretical basis for developing the new kind of high-power terahertz radiation sources. Besides, the related physics mechanisms of the instability are also discussed.

Design and simulation of a gyroklystron amplifier

In the present paper, a design methodology of the gyroklystron amplifier has been described and subsequently used for the design of a typically selected 200 kW, Ka-band, four-cavity gyroklystron amplifier. This conceptual device design has been validated through the 3D particle-in-cell (PIC) simulation and nonlinear analysis. Commercially available PIC simulation code “MAGIC” has been used for the electromagnetic study at the different location of the device RF interaction structure for the beam-absent case, i.e., eigenmode study as well as for the electron beam and RF wave interaction behaviour study in the beam present case of the gyroklystron. In addition, a practical problem of misalignment of the RF cavities with drift tubes within the tube has been also investigated and its effect on device performance studied. The analytical and simulation results confirmed the validity of the gyroklystron device design. The PIC simulation results of the present gyroklystron produced a stable RF output power of ∼218 kW for 0% velocity spread at 35 GHz, with ∼45 dB gain, 37% efficiency, and a bandwidth of 0.3% for a 70 kV, 8.2 A gyrating electron beam. The simulated values of RF output power have been found in agreement with the nonlinear analysis results within ∼5%. Further, the PIC simulation has been extended to study a practical problem of misalignment of the cavities axis and drift tube axis of the gyroklystron amplifier and found that the RF output power is more sensitive to misalignments in comparison to the device bandwidth. The present paper, gyroklystron device design, nonlinear analysis, and 3D PIC simulation using commercially available code had been systematically described would be of use to the high-power gyro-amplifier tube designers and research scientists.

3-D PIC Simulation of Gyrotwystron Amplifier Using MAGIC

In this paper, a 3-D electromagnetic (EM) and particle simulation of an X-band high power gyrotwystron has been reported. The EM (cold) and the electron beam and RF wave interaction (hot) behavior have been studied using a commercially available 3-D particle-in-cell code MAGIC. The EM field analysis guarantees that the RF circuit operation is in the desired TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> at the input cavity and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> circular electric waveguide mode at the output with the desired frequency of operation of 9.8 GHz. The hot simulation demonstrates the particles phase space behavior along the interaction circuit and the energy transfer phenomena. The present gyrotwystron develops an output power ~20 MW with an electronic efficiency of ~21% and a bandwidth of 10% for ideal electron beam velocity.

PIC simulation study of a 35 GHz, 200 kW Gyroklystron

A three-dimensional PIC simulation of a 35 GHz, 200 kW two cavity gyroklystron amplifier has been performed to study the electron beam and RF wave interaction behavior using a commercial PIC code 'MAGIC'. The electromagnetic field analysis of the RF structure in the absence of the electron beam and beam-wave interaction study in the presence of the electron beam have been carried out for the performance evaluation of the device. Electromagnetic field analysis has been done using the eigenmode solver, which ensures the structure operation in the desired TE01 operating mode at 35 GHz frequency. Electron beam and RF wave interaction simulation confirm that the present gyroklystron meet the required specification in terms of output power and gain. Moreover, the particles phase space behavior along the interaction length has been also demonstrated to realize the energy transfer phenomena. An output power around 200 kW at 34.95 GHz with ~35% efficiency and a bandwidth of 0.29% have been obtained considering no spread in electrons velocity. Our simulated result matches with the experimental values within 8%.

About Cherenkov and Cyclotron Wave Excitations by Elliptical Relativistic Modulated Electron Beam in a Cylindrical Plasma Column With Elliptical Cross Section

The excitation of electromagnetic waves due to the interaction of modulated density profile of an elliptical relativistic electron beam with the eigenmodes of a magnetized plasma column with elliptical cross section have been analyzed. Theoretically, it is shown that the Cherenkov and fast cyclotron interactions appear between the beam and eigenmodes of plasma column, and in continuum it is proved that the growth rate of the waves in slow cyclotron interaction will be vanished. The dispersion relation of space-charge waves in density-modulated relativistic electron beam in this configuration will be presented, too.

A Novel V-Shaped Microstrip Meander-Line Slow-Wave Structure for W-band MMPM

In this paper, a novel V-shaped microstrip meander-line slow-wave structure (SWS) is proposed for use in a low-voltage high-efficiency wide-bandwidth miniature millimeter-wave traveling-wave tube (TWT). The electromagnetic characteristics and the interaction between the sheet electron beam and slow wave in this SWS are obtained by utilizing the CST Microwave Studio and Particle Studio codes, respectively. From our calculations, it is predicted that, at a beam voltage of 3.7 kV and a beam current of 100 mA, an output power greater than 30 W can be obtained ranging from 75 to 100 GHz, and this V-shaped microstrip meander-line TWT will be helpful for a W-band millimeter-wave power module.

140 GHz菱形微带曲折线慢波结构行波管的模拟计算

A rhombus-shaped microstrip meander-line slow-wave structure is proposed for use in a low voltage, wide bandwidth, moderate power and high efficiency millimeter-wave traveling-wave tube. The structure is evolved from the original V-shaped microstrip meander-line slow-wave structure. Compared with the conventional slow-wave structure, it is a kind of planar structure, whose fabrication can be easily realized by utilizing the technology of 2-D micro-fabrication. Whats more, the structure can realize beam-wave interaction with sheet electron beam, and no additional electron beam channel is needed. The electromagnetic characteristics and the interaction between the sheet electron beam and slow wave in the structure are obtained by utilizing the electromagnetic simulation software HFSS and the particle-in-cell code in CST Particle Studio, respectively. Our calculations indicate that, at a beam voltage of 7 kV and a beam current of 90 mA, the traveling wave tube based on the structure is capable of delivering several tens of watts output power with an interaction efficiency of 14.3％ and a transient 3 dB bandwidth of 18 GHz(ranging from 132 GHz to 150 GHz)

Hierarchical Asymptotic Methods in the Theory of Cluster Free Electron Lasers

We describe an algorithm for the hierarchic method of averaged characteristics and discuss a practical application of this concept. The application of this method opens new prospects for the solutions of many difficult electrodynamic problems, which, until recently, were considered “unsolved”. We illustrate this method with the example of the effect of plural multi-harmonic parametric resonance of electron-beam waves. This effect can take place within high-current electron beams in the case of the realization of two-stream instability. The considered relativistic beam-model is treated as a model for the transit section of relevant klystron Cluster Two-stream Free Electron Laser (CTSFEL).

Nonlinear transverse-wave interactions in divergent axially symmetric magnetic fields

The dynamics of transverse-wave interactions in intense electron beams in divergent axially symmetric magnetic fields has been investigated by computer simulation. The case of a short magnetic field was analyzed. The conversion of electron-beam transverse waves in the presence of a decelerating electric field was considered.

Investigating the characteristics of an M-type traveling-wave tube in the presence of multifrequency interaction

The model of interaction between an electron beam and electromagnetic waves with complex spectra is described. The correct application of the numerical implementation of the proposed model is investigated and numerical results are presented. Simultaneous amplification of several components of a complex electromagnetic signal in an M-type traveling-wave tube is considered and analyzed.

Transverse electron-beam waves for microwave electronics

A brief discussion is given of the state of the art,challenges, and prospects in the application of transverse (cyclotron and synchronous) electron-beam waves in microwaveelectronic devices, including protectors, parametric and electrostatic amplifiers, tunable filters, circularly polarized travelingwave tubes, microwave/DC converters, and combined interaction klystrons.

Poperechnye volny elektronnogo potoka v mikrovolnovoi elektronike

Poperechnye volny elektronnogo potoka v mikrovolnovoi elektronike

Theoretical analysis of interaction between electron beam and electromagnetic wave for unidirectional optical amplifier

Interaction between an electron beam and an electromagnetic wave is analyzed on the basis of semiclassical quantum mechanics that includes the influence of electron scattering and thermal distribution. The result is applied to determine the gain coefficient of the unidirectional optical amplifier utilizing this interaction. A general formula of the gain is obtained, which is applicable not only to an electron beam in vacuum but also to a semiconductor. The gain in the optical region due to an electron beam in vacuum is calculated, and it is shown that the gain coefficient is strongly reduced by the energy broadening due to scattering. This reduction is more significant for lower frequencies. The thermal distribution of the electron energy also reduces the gain, although the influence is less than that of electron scattering. The gain obtained in the quantum mechanical analysis is compared with that of the classical analysis including electron scattering. The difference between the classical and quantum mechanical analyses approaches zero in the low-frequency limit, while it is large in the optical frequency range.

Quantum theory of a semiconductor klystron

The interaction between a hot electron beam and electromagnetic waves is analyzed in a semiconductor with the structure of the klystron device, in which electrons emit or absorb photons at the input port and then make a spontaneous emission at the output port. As a result of the collective spontaneous emission due to the interference between the specific many-electron states, the output photons have harmonic frequencies of the input, and the emission rate is proportional to square of the beam current. Due to the influence of electron scattering, the output power is much reduced for an input photon energy smaller than the electron energy broadening determined by the scattering and also for an input-output interval larger than the electron coherence length.

Experiments on space-charge waves in electron beams propagating through a resistive-wall channel

Localized longitudinal space-charge waves in a transport channel with a resistive wall are investigated experimentally. The space-charge waves with various pulse widths are generated in electron beams with energies of 3.0–8.5 keV and currents of 30–135 mA, and they are transported through a resistive channel with a resistance of 5–10 kΩ and a length of 1 m. The resistive channel, made of a glass tube with a resistive material coating, is surrounded by a long solenoid which provides the focusing for the beam. The localized space-charge waves are measured with current monitors and energy analyzers at the entrance and exit of the resistive channel, and the wave-amplitude growth and damping rates are determined. The measured results are compared with the theory in the long-wavelength range. For localized waves with short widths, where the long-wavelength approximation is not valid any more, dispersion and distributed capacitance effects on the growth/damping rates are discussed. In addition, preliminary results on the energy width measurements of space-charge waves are presented.

Nonlinear dynamics of electron bunches in the presence of dissipative effects

The transition phase between two nonlinear regimes of electron-beam–wave interaction depending on the amplitude and the nature of the effective dissipation is investigated with the help of numerical simulations. Effective dissipation due to wave escaping to infinity out of the beam–wave interaction region as well as to collisions in the background plasma is considered. If the dissipation is strong enough, the evolution of the electron beam proceeds in a general way, independently of the type of dissipation and of the nature of the considered waves: structures of strongly concentrated electron bunches are formed. These bunches are not trapped in the wave, and decelerate continuously owing to friction on waves: in the presence of dissipation, the usual quasiperiodic exchange of energy between the wave and the trapped particles, which prevents the wave from collapsing, does not occur. Considering beam interaction with a finite number of waves (modulated wave packet), it is shown that, if the dissipation is strong enough, the structure of electron bunches is dynamically stable in a range of times exceeding several characteristic times of their formation.

Influence of thermal velocity distribution on electron beam - backward electromagnetic wave interaction

One—dimensional linear theory of interaction between electron beam and backward electromagnetic wave in transmission line is presented taking into account arbitrary velocity distribution of electrons and allowing correct consideration of finite length of interaction region. Influence of electron velocity spread оn start oscillation regime of low— voltage backward—wave oscillator is analysed. Calculations are carried out for rectangular, Lorentz and Maxwell distributions.