Search

The analysis of the multimode behavior of the interaction cavity for 42-GHz gyrotron is presented here. The in-house developed codes single-mode cold cavity solver (SMCCS) and GYCAD and commercial particle-in-cell (PIC) simulator MAGIC are used in the design and analysis of 42-GHz gyrotron cavity. SMCCS is used for the calculation of cold cavity parameters such as $Q$ factor, resonant frequency, and the axial electric field profile, which are further used in the beam–wave interaction computation. The PIC code is used here for the parametric optimization and time-dependent-multimode beam–wave interaction simulations of the interaction cavity. The mode purity in terms of the electromagnetic power in individual modes is also calculated using the data generated in the beam–wave interaction simulations. The single-mode analysis of the cavity is also performed using the analytical code GYCAD based on the generalized nonlinear theory. The results obtained by the PIC simulator and GYCAD are discussed and compared here. The analysis of the electron beam misalignment, which may occur due to the radial shifting or tilting of the different components during the fabrication of the device, is also performed and the effects on the efficiency, mode competition, and mode stability are discussed in detail. [ABSTRACT FROM AUTHOR]

This article presents the design and analysis of a staggered double-vane (SDV) slow-wave structure (SWS) for $W$ -band amplifier, with 20-dB gain and a very high bandwidth (~25%). The use of dual Bragg reflector at either end of the interaction structure increases the impedance matching and the radio frequency (RF) coupling efficiency at the input and output ports, thereby reducing the RF leakage at the electron gun and collector ends, from 15% to 25% to less than 0.6%. The attenuator section is simple to fabricate and optimally designed in order to provide an effective isolation (>20 dB) between the input RF signal in the input section and the RF signal reflected from the output section. The dispersion analysis, the transmission analysis of each section, and the beam–wave interactions were simulated using the Dassault system’s computer simulation technology (CST) eigenmode solver, time-domain solver, and the particle-in-cell (PIC) solver, respectively. The proposed design of the SDV SWS conclusively provides an enormous bandwidth of ~25 GHz with 20-dB gain for $W$ -band amplifier, when compared to its solid-state counterparts and earlier reported work as per the author’s knowledge. [ABSTRACT FROM AUTHOR]

The coaxial interaction structure for a 0.24-THz, 2-MW gyrotron is designed, and its RF behavior is analyzed for the beam current of 60 A and the beam voltage of 90 kV. The searching of a suitable, very high-order TE mode, which satisfies all the technical conditions required to generate 2-MW RF power, is an important and critical step in the development of a coaxial-cavity (COCA) gyrotron. The detailed analysis of mode selection is described in this article. The geometry of the axially corrugated insert is optimized using an in-house code COCA. Based on the optimized geometry of the coaxial insert and the cylindrical cavity, the coupling coefficient and the start oscillation current are computed to analyze the mode competition for the operating mode TE42,28. The particle-in-cell (PIC) algorithm-based simulation tool is used for the beam–wave interaction computation. Very fine meshing is implemented in the simulations, considering the high frequency and fine geometry of the coaxial insert. The electron beam parameters and the cavity magnetic field are optimized first aiming at the RF power ≥2 MW and frequency 240 GHz. The final results of the cavity design confirm 2.2-MW RF power and 239.975-GHz frequency at 9.74-T magnetic field. [ABSTRACT FROM AUTHOR]

Inverse magnetron injection gun (IMIG) provides several advantages over simple MIG especially in high-power, high-frequency gyrotron. Sub-millimeter (>230 GHz), high-power (≥1 MW) gyrotrons would be required in futuristic plasma fusion machines to fulfill the need of tens of megawatt RF power for electron cyclotron resonance heating. Here, in this paper, an IMIG is designed for 0.24-THz, 1-MW gyrotron. First, the tradeoff design equations and technical constraints are used to synthesize the electrodes geometry and electrical parameters of IMIG. This synthesized IMIG model is further simulated to finalize the design using electron trajectory code EGUN. Simultaneously, the magnet system including the auxiliary gun coils and superconducting magnets (SCM) is also designed and the obtained magnetic field profile is used in the IMIG simulations. In the case of high-power MIG, the suppression of the beam halo is a major design concern and analyzed critically in the present IMIG design. The shape of the modulating anode and main anode is optimized to make a beam halo shielding. This IMIG is designed for a very high-order mode (TE46,17) simple cylindrical cavity, which confines the range of the tolerance in the electron beam parameters. So, a detailed parametric and misalignment analysis is also performed with respect to the electron beam parameters, such as pitch factor, velocity spread, and guiding center radius spread. These parametric and misalignment analyses would be utter helpful in the fabrication, assembling and testing of the IMIG as well as gyrotron. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for computation of high-order axial modes (HOAMs) in a conventional and uptapered gyrotron resonator. A code has been developed which computes the eigenfrequency, Q-factor and axial field profile of HOAMs in the absence of electron beam in the resonator. Cyclic coordinate search method has been used for the optimization of complex eigenfrequencies, which obviates the computation of gradients of radiation boundary conditions and, hence, reduces computational complexity. HOAMs have been computed for resonators operating at 10, 132, 203, and 424 GHz, and the results obtained have been found to be in good quantitative agreement with the experimental and numerical data available in the published literature. Broadband continuous frequency tuning bandwidth found for subterahertz resonators also agrees well with the published results. HOAMs computed for 1-THz gyrotron resonator designed at CSIR-CEERI have also been presented. [ABSTRACT FROM AUTHOR]

In this paper, the design and development of magnetron injection gun (MIG) for 170 GHz, 1-MW gyrotron have been presented. The triode-type MIG at 80-kV beam voltage and 40-A beam current has been designed and developed. A gun-collector test module for 170-GHz gyrotron has been developed and vacuum processed at 400 °C with continuous 48 h operation. The cathode activation and high-voltage breakdown testing have also been carried out up to desired rating. The simulation result of MIG by EGUN has been validated with 2-D-code TRAK. [ABSTRACT FROM AUTHOR]

Magnetron injection gun (MIG) is an important and critical part of any gyrotron. The overall performance of gyrotron deeply depends on the quality of gyrating electron beam. In this article, the design of triode type magnetron injection gun for 200 GHz frequency tunable gyrotron is discussed. It is planned to design and develop a 200 GHz gyrotron for 300 MHz DNP-NMR spectroscopy. The triode MIG is designed in such a way that it can be used in 200 GHz gyrotron of higher RF power for other applications also such as electron spin resonance, imaging. First, geometrical and electrical parameters of MIG are calculated using trade-off and scaling equations. Based on the calculated parameters, further, electron beam trajectory simulations are performed in EGUN. The geometry of electrodes are optimized through numerous simulation iterations to achieve the required beam parameters, such as, minimum spread in velocity and guiding center radius, an optimum value of velocity ratio (1.3–1.5), guiding center radius as per the maximum beam-wave coupling strength. The magnet system is designed to achieve the smooth Gaussian type of magnetic field profile with peak value of 7.35 T at cavity center. Further detail parametric analyses are performed which would be helpful in the frequency tuning and long-time stable operation of gyrotron device. [ABSTRACT FROM PUBLISHER]

Researchers have investigated plasma-related phenomena and internal breakdowns in the gigawatt–terahertz relativistic backward wave oscillator (RBWO) caused by field emissions from the surfaces of the waveguide circuits in these oscillators. In order to increase the power-handling capability of relativistic electron beam devices, an RBWO is proposed in the form of an oversized structure in which the diameter ( $D$ ) of the electrodynamic structure is increased to several times the free-space wavelength ( $\lambda )$ . An optimal periodic rectangular corrugation structure of which the axial mode is matched to the $\pi $ mode is designed in order to determine only the TM01 mode without mode competition in a slow-wave structure (SWS). The oversized RBWO has a fairly large diameter and uses a resonant reflector to achieve optimum efficiency while also preventing mode competition in the SWS. Absorption of a decelerated electron beam is achieved by the collector, which protects against breakdown and damage. The results of 0.5–0.1 THz from 500 kV–5 kA in the relativistic region are observed by means of a particle-in-cell simulation, and the dispersion relationship is determined by a finite-difference time-domain simulation. The outcomes show that a high-power oversized RBWO can control the selection of the mode and the interaction efficiency. [ABSTRACT FROM PUBLISHER]