Beam-wave Interaction Analysis Research Articles

170-GHz, 2-MW Coaxial-Cavity Gyrotron Design for Plasma Fusion System

Multimegawatt RF power in millimeter waveband (30–300 GHz) is required in the magnetically confined plasma fusion reactors. In this paper, the design of 170-GHz, 2-MW gyrotron with coaxial-cavity configuration is discussed. The mode selection and optimization of corrugation geometry of the coaxial insert are performed and discussed in detail. The beam-wave interaction computation and interaction cavity design are carried out using a particle-in-cell code. The beam-wave interaction analysis confirms 2.2-MW RF power at the 170.07-GHz frequency with more than 40% interaction efficiency. A 5.5-MW coaxial magnetron injection gun (C-MIG) is designed to launch the gyrating electron beam at the first radial maxima of the electric field peak of the selected operating mode in the interaction cavity. The magnetic system consisting of auxiliary coils and superconducting coils is also designed as per the requirement in MIG design.

Design and Characterization of a W-Band Folded-Waveguide Slow-Wave Structure

A single-section slow-wave structure for a W-band folded-waveguide traveling-wave tube with operating bandwidth of around 4% was designed for delivering the output power of 50 W at the operating voltage of 13.5 kV and operating beam current of 80 mA. The design was carried out using analytical formulations and 3D electromagnetic simulations. The beam-wave interaction analysis was carried out using large signal Lagrangian analysis and particle-in-cell simulation. The folded-waveguide slow-wave structure along with input-output couplers and RF windows were fabricated. Cold test measurements were carried out for dispersion characteristics of the slow-wave structure and voltage standing-wave ratio and insertion loss characteristics of the RF window. The measured cold circuit parameters show close agreement with the analysis.

H-Plane and E-Plane Loaded Rectangular Slow-Wave Structure for Terahertz TWT Amplifier

A novel miniaturized rectangular slow-wave structure (SWS), composed of both H-plane and E-plane corrugations, is proposed for submillimeter or terahertz vacuum electron traveling-wave tube (TWT) devices. The advantage of this SWS is to enhance the interaction impedance, therefore, resulting in higher gain and improved output power of the device. In addition, this structure geometry permits design flexibility to achieve a better dispersion behavior (linear dispersion and wider bandwidth) and easy fabrication by available microfabrication processes. Incorporating an H-plane and E-plane load in the SWS design, we achieved a higher performance TWT amplifier with the central frequency of 400 GHz. Both electromagnetic characteristics and beam–wave interaction analysis are investigated using the 3-D electromagnetic software Computer Simulation Technology studio. The simulation results show that an enhanced interaction of the SWS is obtained, and the amplifier has wide instantaneous bandwidth of 80 GHz and 19.5-dB small signal gain at 400 GHz for 17-kV beam voltage and 20-mA beam current. A saturated output power of more than 19 W is obtained from the large-signal simulations.

A 3-D Large Signal Model for Sheet Beam Traveling Wave Tubes

A 3-D frequency domain large signal code called sheet beam traveling-wave tube 3-D (SBTWT3-D) for illustrating the nonlinear beam-wave interaction in the SBTWT is presented in this paper. A recent published field theory model for illustrating the staggered double-grating arrays waveguide (SDGAW) slow-wave structure is adopted in the code to obtain the RF circuit fields' distribution and ohmic loss. The sheet beam is simulated by a set of discrete rays. The ac and dc space-charge fields are obtained by solving the discrete Helmholtz equations and the discrete Poisson equation, respectively. A 3-D nonlinear beam-wave interaction analysis for a W-band SDGAW SBTWT is performed and the calculation results are compared with those obtained from time-domain 3-D particle-in-cell simulations.

Design and Simulation of Lossy Interaction Structure for Ka-Band Gyro-TWT

In this paper, beam-wave interaction analysis in a Ka-band periodically ceramic loaded gyrotron traveling-wave tube (gyro-TWT) amplifier is investigated using particle-in-cell (PIC) simulation. The simulations predict that the interaction structure can produce more than 80-kW output power, 50-dB saturated gain, and 3-dB bandwidth is 2.56 GHz for 65 kV and 5-A electron beam with velocity ratio $(\alpha)$ of 1.2. The dispersion and interaction impedance characteristics of the ceramic-loaded gyro-TWT amplifier are also determined using 3-D simulator CST-microwave studio. This paper describes the design and simulation of a high performance 35-GHz ${\rm TE}_{01}$ mode gyro-TWT that applies the same technique of employing a periodic dielectric loaded interaction structure to achieve stability and wide bandwidth. The stability of this gyro-amplifier is excellent and demonstrates that the ceramic loading is highly effective for suppressing the spurious oscillations in gyro-TWT.

Beam-wave interaction analysis of a magnetically insulated line oscillator

Magnetically insulated line oscillator (MILO) using a metal disc-loaded coaxial cylindrical waveguide as its RF interaction structure is field analyzed for the beam-wave interaction using the linearized Vlasov equation. The beam present dispersion relation of the device is obtained applying the modal matching technique which is further used to estimate the oscillation frequency, temporal growth rate, output energy, and other device parameters. Further, MILO is simulated using commercial pic code “magic,” and the electron momentum and energy plots are found to be in agreement with those obtained through the present analysis within 5%. Furthermore, the device temporal growth rate reported in the literature for the experimental MILO device is also compared with the present analytical theory and found in agreement ∼5%.

Design of 95 GHz, 2 MW Gyrotron for Communication and Security Applications

The design and the numerical simulation of the 95 GHz, 2 MW gyrotron for various kinds of communication, sensing and security applications is presented. The gyrotron is designed for the TE24,8 operating mode. Various in-house developed and commercially available computer codes are used for the design purpose. A 4.25 MW electron gun is designed for the 2 MW of output power. The mode selection, cold cavity and the beam–wave interaction analysis are discussed for the design of weakly tapered open resonator type of interaction cavity. The parametric analysis of the interaction cavity and the electron gun is also presented.

Particle-in-Cell Analysis of 1 MW/110GHz Gyrotron Interaction Cavity

In this paper, the design and numerical analysis of the interaction cavity for 1MW, 110 GHz gyrotron is presented. The in-house developed code GCOMS and the commercially available 3D particle-in-cell simulation code MAGIC have been used for the mode selection and optimization of the interaction cavity parameters respectively. TE22,6 mode has been chosen as the operating mode. The cold cavity and the beam-wave interaction analysis have been carried out for the TE22,6 mode and the output power and the efficiency have been computed. The sensitivity analysis of the output power and the efficiency has also been performed with respect to the cavity geometry and the electron beam parameters. More than 1MW output power has been achieved at 110 GHz frequency with the selected operating mode.

Design of 84 GHz 500 kW Gyrotron for Technological Millimeter Wave Applications

In this paper, the design and the numerical simulation of the 84 GHz, 500 kW gyrotron at first harmonic operation for technological applications is described. The operating mode of the gyrotron is TE10, 4. Various in-house developed and commercially available computer codes are used for the design purpose. The triode-type magnetron injection gun with the accelerating voltage 70-kV, the beam current 10-A and the maximum transverse velocity spread less than 5% is designed. The preliminary design is obtained by using some trade-off equations. The mode selection, the cold cavity and the beam-wave interaction analysis are discussed for the design of weakly tapered open resonator type of the interaction cavity. The parametric analysis of the interaction cavity and the electron gun is also presented.

Particle-in-cell analysis of beam-wave interaction in gyrotron cavity with tapered magnetic field

A commercially available electromagnetic simulator — MAGIC, a particle-in-cell (PIC) code — has been used to carry out a comparative study of the beam-wave interaction under uniform and tapered magnetic field profiles of a 42 GHz, 200 kW gyrotron. The magnetic field profile across the resonant cavity varies by ±6.5% with a peak value of 1.615 T. The MAGIC simulation shows the desire performance of the gyrotron under both magnetic field conditions with an operating mode TE03 and a pitch factor of 1.26. The analysis of the simulated results show that stability in the power growth was reached more quickly and achieved higher output power in the case of a tapered magnetic field.

Numerical Analysis of Interaction Cavity for 1.5 MW/127.5 GHz Gyrotron

This paper presents the design of 127.5 GHz ITER start-up gyrotron interaction cavity. Particle-in-Cell electromagnetic simulation approach has been used for the cold cavity and beam-wave interaction analysis. In-house developed code GCOMS has been used for the mode selection. TE24,8 mode has been chosen as the operating mode. The simulation results show the output power more than 1.5 MW at the operating frequency of 127.8 GHz and the cavity centre magnetic field of 5.1 T. The study of the parametric dependency of the output power and the effi- ciency on the electron beam and the cavity geometry parameters has also been carried out.

Beam-wave interaction analysis of gyrotron-traveling-wave tube based on a lossy dielectric-lined waveguide

A lossy ceramic-loaded waveguide is positive to promote the stability and performance of the gyrotron traveling-wave amplifier (gyro-TWT). In this paper we develop the electron cyclotron maser linear theory on the basis of the field expressions in the lossy ceramic-loaded waveguide. By systematic numerical calculation, we find that both the field patterns and the dispersion curves have one-to-one mapping relation between the modes in ceramic-loaded waveguide and that in empty cylindrical waveguide. With the Laplace transform, the linear theory could calculate the field profile and the threshold of an absolute instability oscillation. The linear theory is also used to study the influence of the magnetic, current and ceramic layer on the amplification characteristics. These results are promotive to the application of the lossy ceramic in a gyro-TWT and the development of the high stable gyro-TWT.

Beam-wave interaction analysis in the coupled double cavity gyrotron oscillator

General equation of electron-wave synchronous interaction is obtained in gyrotron oscillator, in which the effects of guiding center drift and phase of RF field profile is considered. The interaction efficiency is calculated for the second harmonic operation of single TE021 mode for a double cavity gyrotron oscillator model, in which the RF field profile and operating parameters of the gyrotron oscillator are regulated in order to get optimum efficiency. It is shown that the efficiency of 53 percent can be obtained for α =1.5. The characteristic of the double cavity configuration is discussed. The bunching processes of the double cavities are compared with that of single cavity. The effects of guiding center drift and RF field profile phase on the beam-wave interaction are analysed.