Electron Beam-wave Interaction Research Articles

Electromagnetic Particle Algorithm for Beam–Wave Interaction in Traveling Wave Tube of Symmetry

In many fields, such as space astrophysics, plasma and vacuum electronics, there are many nonlinear strong coupling physical problems. In order to solve the problem of electron beam–wave interaction in cylindrical Traveling wave tube (TWT) with symmetrical structure, a multi particle simulation algorithm for beam circuit is designed. The algorithm allows aperiodic time input, nonuniform linearity and large space diagnosis for different particles. In this algorithm, the field of coupled slow-wave transmission line is simulated by finite difference method. Assuming that there is strong coupling between the beam and the circuit, the space center equation of transmission along the line is obtained, and the space charge field is modeled considering the space charge effect, which can easily be ignored. The Particle In Cell (PIC) method of frog leaping step scheme is adopted to evaluate the electric field of each particle center, determine the circuit and space charge field, and design the termination part to compensate for the loss in order to avoid self-excited agitation. Finally, a simple numerical simulation is carried out for the electromagnetic problem and the accuracy of the code is checked against the electromagnetic simulator CHPIC. Therefore, the algorithm can be used to solve the problem of beam–wave interactions in a fixed structure (cylindrical) in multiple fields and can accurately record the data in the process.

Control of sub-terahertz gyrotron frequency by modulation-anode voltage: Comparison of theoretical and experimental results.

This paper presents a comparison of simple self-consistent theory data and experimental results aimed to study the influence of the anode voltage on the frequency of the subterahertz gyrotron with the goal of frequency stabilization. Numerical simulations of the electron beam formation and beam-wave interaction in a 0.26 THz gyrotron are performed. The experimental dependence of the gyrotron frequency tuning on mod-anode voltage is in agreement with theoretical predictions.

Design of a High-Gain $X$ -Band Megawatt Gyrotron Traveling-Wave Tube

In this paper, a lossy dielectric-loaded high-gain $X$ -band gyrotron traveling-wave tube (gyro-TWT) which operates at the fundamental circular TE11 mode is designed and analyzed. The designed gyro-TWT has the features of high-gain and megawatt level output power. Lossy dielectric is applied to suppress spurious oscillations and to improve the stability of the gyro-TWT. In addition, the interaction behavior of the electron beam is investigated. In the condition of 4.5 W input power, a peak RF output power of 2.14 MW with a gain of 56.7 dB at 8.4 GHz is predicted, corresponding to the electron beam-wave interaction efficiency of 35.6% at 150 kV, 40 A. The research also obtains stable output power over 1.5 MW in the range of 8–8.4 GHz with 2-W input power and output power over 1.2 MW with 150-W input power in the range of 8.6–9 GHz.

Starting Currents for Eigenmodes of a Gyrotron Cavity With Mode Conversion

In the fixed-field (cold) approximation, a generalized formula is derived for the starting currents of eigenmodes excited by an electron beam in a gyrotron cavity with the mode conversion. Tapered gyrotron cavities with gradual and abrupt transitions are considered as examples. It is shown that the effect of the mode conversion on the starting current consists mainly in the change of the diffractive quality factor and, therefore, is small for cavities with low diffractive losses. For such cavities, our formula is in good agreement with single-mode, self-consistent (hot) calculations of the electron beam–wave interaction. The agreement degrades for high-order axial modes having clear-cut distinctions of cold and hot fields. The derived formula is used to test the validity of the single-mode approximation for a complex gyrotron cavity with the abrupt change in radius.

Controllable Thermal-Frequency Tuning of a Terahertz Gyrotron

Gyrotron performance is sensitive to cavity structure parameters, and the cavity shape is temperature dependent due to thermal deformation induced by temperature rise from ohmic loss power on finite-conductivity cavity wall. Accordingly, this paper studies a frequency-tuning scheme for terahertz gyrotron by properly controlling the cavity thermal deformation. By combining gyrotron nonlinear theory and finite-element method software, controllable thermal-frequency-tuning capability of a continuous-wave 263-GHz gyrotron is systematically investigated, toward maintaining gyrotron operating under gyromonotron condition in frequency-tuning band, and achieving high efficiency in broadband frequency-tuning range. After studying cavity thermal distribution, structure deformation, and electron beam–wave interaction, an optimized cavity structure with transition sections on both ends is proposed. Simulation predicts that with the two-transition-section cavity, via additional thermal tuning, the continuous-frequency-tuning band is capable of reaching 1.75 GHz, which is 5 times of the initial bandwidth. Furthermore, using the thermal-frequency-tuning technology, impressive high efficiency above 17% is obtainable in the whole frequency-tuning range.

Theoretical analysis and Vsim simulation of a low-voltage high-efficiency 250 GHz gyrotron

Low-voltage, high-frequency gyrotrons with hundreds of watts of power are useful in radar, magnetic resonance spectroscopy and plasma diagnostic applications. In this paper, a 10 kV, 478 W, 250 GHz gyrotron with an efficiency of nearly 40% and a pitch ratio of 1.5 was designed through linear and nonlinear numerical analyses and Vsim particle-in-cell (PIC) simulation. Vsim is a highly efficient parallel PIC code, but it has seldom been used to carry out electron beam wave interaction simulations of gyro-devices. The setting up of the parameters required for the Vsim simulations of the gyrotron is presented. The results of Vsim simulations agree well with that of nonlinear numerical calculation. The commercial software Vsim7.2 completed the 3D gyrotron simulation in 80 h using a 20 core, 2.2 GHz personal computer with 256 GBytes of memory.

A 650-GHz Backward Wave Oscillator Based on Axial Loaded Double Defected-Photonic Crystal SWS

Axial loaded Double Defected Photonic Crystal (ADD-PC) with a cylindrical beam channel is introduced as a slow-wave structure (SWS) for backward wave oscillator (BWO) source design. The structural and the geometrical dimensions of the proposed SWS for submillimeter wave regime are realizable using the modern microfabrication processes. Starting from the basic design; the dispersion diagram, the modal phase velocity, and the beam interaction impedance are calculated. The effect of fabrication tolerance on both the operating frequency and the beam interaction impedance is also discussed. Using a custom built numerical electron beam–wave interaction algorithm, the electromagnetic field generation supported by the ADD-PC SWS is analyzed thoroughly. Simulation results indicate that with the proposed BWO, an output power of almost 8 W at 650 GHz with 1.8% conversion efficiency can be achieved.

Control of the Operation Mode of a Relativistic <italic>Ka</italic>-Band Backward-Wave Oscillator

Variations in the transient time and in the microwave pulse duration and peak power have been demonstrated for a relativistic subgigawatt Ka -band backward-wave oscillator (BWO) with the slow-wave structure geometry, the accelerating voltage, and the electron beam current remained unchanged. This was done taking into account that the BWO operation mode depends on the starting-current-to-beam-current ratio. Efficient variation of the starting current was attained by changing the beam path in view of a significant difference between the times of the guide pulsed magnetic field diffusion into the electron injection region and beam-wave interaction space.

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%.

The electron optics system and beam-wave interaction for novel W-band sheet beam klystron

The cold fluid model theory was used for studying the transport and its instability for the sheet electron beam in the uniform magnetic field.The results show that if the focusing magnetic field and the filling factor of the beam in tube are increased,the Diocotron instability will be decreased to achieve a transportation in a long distance.Based on above results,3D simulation method was employed to design and optimize the electron optics system for the W-band sheet beam klystron.2D macro-particle model for sheet electron beam was proposed to develop a beam-wave interaction simulation program code for SBK,named SBK2D.The beam wave interaction processes in the W-band SBK with 8 multi-gap cavities are calculated using the SBK2D.The simulation indicated that a 69 kW peak power output at high frequency with efficiency of 24%,gain of 37 dB,and 3dB bandwidth of 100MHz at 3 dB can be derived.The W-band sheet beam tube was manufactured according to the design.The transmission rate and cross-section experiments were performed with the beam voltage in the range of 20~82 kV,beam current of 0.5~4.27A,and the length of tunnel of 100mm.More than 98% transmission rate with the beam cross-section about 10mm×0.5mm were obtained.

High-Power Tunable Terahertz Radiation by High-Order Harmonic Generation

We propose a new type of terahertz (THz) radiation source based on the electron beam-wave interaction. A high-order harmonic-generation process was introduced to a traveling-wave tube (TWT)-like device-the high-harmonic TWT or HHTWT. The scheme is configured as a frequency multiplier and amplifier with W-band (millimeter wave) input signals and THz output power. Simulations show that operation at the seventh harmonic is possible and other order harmonic waves were suppressed. The output frequency can be tuned continuously over a 30-GHz bandwidth with more than 20-dBm output power. The peak output power is about 30 dBm at 707 GHz. The output frequency is insensitive to beam voltage jitter.

Generation of high-power tunable terahertz-radiation by nonrelativistic beam-echo harmonic effect

A new type of terahertz radiation source based on the nonrelativistic electron beam-wave interaction is proposed. Here, the beam echo harmonic effect is applied to a traveling wave tube like device. The scheme is configured as a combination of a frequency multiplier and amplifier with, for instance, W-band (millimeter wave) input signals and terahertz output power. A one-dimensional model of this device shows that a 10th order harmonic-wave can be generated while other harmonic waves are suppressed. The device only requires a readily available input source (W-band), and the output frequency can be tuned continuously over a wide band.

A time-dependent nonlinear theory and simulation for gyroklystron amplifier

A time-dependent nonlinear theory for gyroklystron amplifier is presented. The theory includes a time-dependent description of the electromagnetic fields and a self-consistent analysis of the electrons. The generalized telegrapher equations represent the electromagnetic fields. The equations of motion of the electrons are described in the framework of the guiding-center approximation. All trajectories are calculated and used as current sources for the fields. The nonlinear theory of interaction is investigated in which mode coupling is taken into account in varying wall radius. Transverse velocity of the electrons from the gyroklystron amplifier satisfies Gaussian distribution. Distribution model of the velocity spread in the gyroklystron amplifier beam-wave interaction is established. A code for the self-consistent nonlinear beam-wave interaction is developed based on the presented theory. The electron beam-wave interaction of a Kα band gyroklystron amplifier is thoroughly studied and analyzed by the code. Numerical verification using MAGIC simulation is also given. The numerical results are in good agreement with the self-consistent nonlinear simulations.

Study on the dispersion relations of a relativistic annular electron beam guided by a finite axial magnetic field

The relativistic annular electron beam guided by a finite axial magnetic field is studied in this paper, in which the electron beam is considered as a special media. Making use of the constitutive transformation and the Lorentz transformation in the four-dimensional space, the permittivity tensor of the stationary magnetized plasma, the permittivity tensor, the permeability tensor and the chiral tensor of the electron beam in the rest (laboratory) frame are acquired. And the boundary conditions, including the surface current density due to the ripple of the beam, have been obtained. As an example of the applications of this approach, the dispersion relations of a relativistic annular electron beam guided by a finite axial magnetic field in a waveguide has been studied. The results of numerical calculation show that the present approach is more accurate and can provide clearer mode information for the electron beam. In addition, the results also show the axial magnetic field can affect the dispersion curves of space charge wave via the surface current density of an electron beam. Thus this approach can be exploited in a number of electron beam-wave interaction systems, including some kinds of free electron devices, plasma filled Cherenkov radiated free electron lasers and masers.

Linear theory of the electron beam-wave-plasma interactions in a magnetized plasma waveguide

The theoretical study on the electron beam-wave interactions in a plasma waveguide immersed in a finite magnetic field is given in the article, in which both the plasma and the electron beam are considered as special media. Making use of the constitutive transformation and the Lorentz transformation in the four-dimensional space, the permittivity tensor of the stationary magnetized plasma, the permittivity tensor, the permeability tensor, and the chiral tensor of the electron beam in the rest (laboratory) frame are acquired. Therefore, two coupled wave equations for the magnetized plasma and electron beam have been obtained and the dispersion relations are then achieved by solving these coupled equations together with the boundary conditions including the surface current density due to the ripple of the plasma/beam. As an example of the applications of this approach, the beam-wave interactions in a practical plasma Cherenkov maser have been studied and the numerical calculations have been carried out in detail. It has been found that the present approach is more accurate and can provide clearer mode information for the electron beam-wave interactions in a magnetized plasma waveguide. This approach can be exploited in a number of electron beam-wave interaction systems including some kinds of free electron devices, plasma filled Cherenkov radiated free electron lasers and masers.

Basic theoretical formulations of plasma microwave electronics. I. A fluid model analysis of electron beam-wave interactions

This two-part paper presents the first complete, generalized basic theoretical formulation for electron beam-wave interactions in a plasma-filled (corrugated or smooth-walled) waveguide immersed in a finite magnetic field. The general interaction and dispersion equations of the longitudinal and transverse interactions in both smooth and corrugated magnetized plasma-filled waveguides (MPWs) are formulated. Our approach differs from that of previous investigators in that we begin by first deriving the dispersion relation of an MPW and then using the resulting electromagnetic fields, which embody the plasma effects, as the basis field vectors. We then investigate the underlying interactions with a superimposed electron-beam in a variety of microwave device configurations. For example, we examine plasma Cherenkov radiation, the plasma-filled travelling-wave-tube/backward-wave-oscillator (TWT/BWO), the plasma-filled electron cyclotron resonance maser (ECRM), and other beam-wave interactions including those involving ion-channels. Some possible new interactions in a magnetized plasma-filled waveguide (MPW) are proposed. A detailed discussion and analysis of the important physical role of the plasma background are given. Many interesting features of beam-wave interactions in an MPW are pointed out, three of them being most essential. One is that transverse interactions are always accompanied by longitudinal interactions. The second is that the magnetized plasma itself is strongly involved in the interaction mechanisms via an additional component of the field. The third interesting feature is that the plasma-filled ECRM prefers to operate at high cyclotron harmonics. The first part of this two-part paper presents formulations using a fluid model for both the plasma and the beam. It also includes a detailed treatment of the physical effects of the ion channel that is formed in the plasma by an intense electron beam. Part II extends the analyzes by retaining a fluid treatment for the plasma-fill but substituting a kinetic theory treatment for the electron beam. This kinetic theory model should be used when the velocity spread of the beam's electrons must be taken into account. The theory presented in both parts of this paper is based upon the "given field" approach that has been widely used successfully in science and technology, in particular in microwave electronics. In both parts of the paper, sample numerical calculations are also presented in order to illustrate the physics.

Basic theoretical formulation of plasma microwave electronics. II. Kinetic theory of electron beam-wave interactions

For pt.I see ibid., vol.28, no.6, p.2135-51 (2000) Building upon the theoretical foundations presented in Part I of this paper, the kinetic theory of electron-beam-wave interactions in a magnetized plasma-filled waveguide (MPW) is presented in this second part. This kinetic theory treatment is more generally applicable to cases of less-intense electron-beams (Montgomery and Tidman, 1964). The dispersion relations for longitudinal and transverse interactions, in both smooth and corrugated waveguides, are all derived by using kinetic theory to model the e-beam dynamics. This includes kinetic theory treatments of the plasma filled electron cyclotron resonance maser (ECRM) and a combination of Cherenkov-cyclotron resonance phenomena. It is important to note that in an MPW, transverse interactions (e.g., ECRM interactions) are always coupled with longitudinal interactions. Using the kinetic treatment is essential for studying the ECRM because its energy conversion mechanism is based on azimuthal phase bunching and finite Larmor radius effects. The dispersion relation that we derive shows that the presence of a plasma-fill tends to increase the growth rate of the waveguide mode ECRM instability.