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The cell-type continuous electromagnetic radiation system is a demonstration device capable of generating high-power millimeter electromagnetic waves of a specific wavelength and observing their effects on living organisms. It irradiates a biological sample placed in a 30 x 30 x 50 cm³ cell with electromagnetic waves in the 3.15-mm-wavelength region (with an output of ≥1 W) and analyzes the temperature change of the sample. A vacuum electronic device-based coupled-cavity backward-wave oscillator converts the electron energy of the electron beam into radiofrequency (RF) energy and radiates it to the target through an antenna, increasing the temperature through the absorption of RF energy in the skin. The system causes pain and ultimately reduces combat power. A cell-type continuous electromagnetic radiation system consisting of four parts--an electromagnetic-wave generator, a high-voltage power supply, a test cell, and a system controller--generates an RF signal of ≥1 W in a continuous waveform at a 95-GHz center frequency, as well as a chemical solution with a dielectric constant similar to that of the skin of a living organism. An increase of 5 °C lasting approximately 10 s was confirmed through an experiment. [ABSTRACT FROM AUTHOR]

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]

A 42-GHz, 200-kW gyrotron was developed and tested for the Indian plasma fusion system. The gyrotron was designed for the TE0,3 operating mode. The configuration of the triode-type magnetron injection gun (MIG) with the linear RF output, undepressed collector, and face-cooled double disk window was adopted in this gyrotron because of the first development experience. The complete tube was developed and processed at Central Electronics Engineering Research Institute (CEERI), Pilani, India. The RF testing of the gyrotron was performed at the participating institute, Institute of Plasma Research (IPR), Gandhinagar, India. Due to some cooling issues in the collector region, the tube was tested by a resistive capacitor network-based power supply for a very short pulse in place of a long pulse, high voltage power supply. The tube was tested up to the beam voltage of 51 kV and a beam current of 12 A at the cavity magnetic field of 1.61 T for the short pulse of $500~\mu \text{s}$. The tube was inserted into the magnet system consisting of a main electromagnet, auxiliary gun coils, and collector magnets. The multi-hole and single hole couplers were used to measure the RF power in the TE0,3 mode and the overall power, respectively. The measured results were also compared with the simulated results and a close agreement of the results was found. The short pulse testing confirms the electrical design and the development approach for the 42-GHz gyrotron tube. [ABSTRACT FROM AUTHOR]

The 42-GHz gyrotron cavity had three sections in its final design: down-taper section, up-taper section, and uniform middle section. The design of the cavity depends on the RF mode and desired power growth. The finalized design parameters of down-taper and up-taper angles are 2° and 3°, respectively, with respect to the middle section of gyrotron cavity. This cavity consists of these poorly tapered sections at both the ends of midsection. The combination of all three sections results into a complex cavity structure which is complicated and challenging to fabricate. An additional challenge in fabrication is to achieve desired designed parameters. Therefore, design realization through fabrication clearly needs dimensional measurement. The dimensional parameters of cavities such as down-and up-taper angles, uniform section diameter, taper lengths, and surface roughness measurement have their own significance and importance. This paper presents the destructive and the nondestructive methods to measure the dimensional parameters of a complex cavity structure. Further, a computational analysis is also done to represent the comparisons between the design and measured values in terms of ohmic quality factor and efficiency and reported the effects of geometrical changes. [ABSTRACT FROM AUTHOR]

A klystron is an important vacuum device which is useful in medical linear accelerators because it amplifies the radio-frequency (RF) signals required to produce high-energy particle beams. The properties of the nonlinear input and output dynamics in the klystron circuit arouse distortion in various types of parameters pertaining to the beam voltage, beam current, RF power, and operating frequency from unpredictable external factors. Therefore, low-level RF (LLRF) control systems can facilitate the regulation of the output of the klystron to a desired level. Low-level RF control system of the klystron is designed to stabilize the applied voltage and control the resonance frequency of the cavity of the klystron. In this work, an infallible low-level RF control system, the most suitable for a klystron, is designed to use a beam monitoring and an interlock system with components that include an isolator and a phase shifter. Moreover, with regard to pulse distortion at the flap top at the RF output power, the stability of the RF power pulse at the flap top part was improved somewhat by a variable inductor which controlled the inside of the pulse modulator. In this LLRF control experiment, the pulse modulator generated 140kV-95A and succeeded in generating RF output power of 2.856GHz-6MW level of an S-band klystron. During this process, the efficiency of the RF power was approximately 42∼45% and the pulse repetition rate was 10 Hz. The flattop pulse width was measured and found to be 1 µs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, we present the RF behavior of conventional cylindrical interaction cavity for 240 GHz, 1 MW gyrotron for futuristic plasma fusion reactors. Very high-order TE mode is searched for this gyrotron to minimize the Ohmic wall loading at the interaction cavity. The mode selection process is carried out rigorously to analyze the mode competition and design feasibility. The cold cavity analysis and beam-wave interaction computation are carried out to finalize the cavity design. The detail parametric analyses for interaction cavity are performed in terms of mode stability, interaction efficiency and frequency. In addition, the design of triode type magnetron injection gun is also discussed. The electron beam parameters such as velocity ratio and velocity spread are optimized as per the requirement at interaction cavity. The design studies presented here confirm the realization of CW, 1 MW power at 240 GHz frequency at TE mode. [ABSTRACT FROM AUTHOR]

A helix slow-wave structure (SWS) for a high-efficiency (electronic efficiency > 25%) Ku-band 140-W space traveling-wave tube (TWT) has been designed. The cold circuit parameters of helix SWS, like propagation constant and on-axis interaction impedance, were determined using 3-D electromagnetic field simulators ANSOFT-HFSS and CST-MWS, and those were validated with the experimental results. The in-house developed large-signal code SUNRAY-1D was used to design a complete helix SWS in two sections with sever and taper to achieve desired output power, gain, efficiency, and other linearity parameters like phase shift, AM/PM factor, and I/M components. The simulated RF performance of the Ku-band 140-W helix TWT was validated with the experimental results. A close agreement between the simulated and experimental results has been found. [ABSTRACT FROM PUBLISHER]

A review on the sub-THz/THz gyrotrons is performed in this manuscript. The present development status of gyrotrons can be divided into three streams for the sake of better understanding: 1. low frequency (<35 GHz), medium power (<100 kW), small size and easy to handle gyrotrons for industrial applications, 2. very high power (1 MW or more), medium frequency (100–200 GHz) gyrotrons for plasma fusion applications, 3. low power (few tens of watt to kW), high frequency (>200 GHz) gyrotrons for various innovative applications. In this manuscript, the third stream of gyrotron development is reviewed. In last few decades several innovative applications are searched in sub-THz/THz band where the gyrotrons could be used as an efficient source of RF radiation. The applications of sub-THz/THz gyrotrons including the futuristic scope of the device are also discussed in this article. Further, several criticalities arise in the design and development when the gyrotron operation shifts toward the high frequency band. Various such design and technological challenges are also discussed here. Finally the development status of sub-THz/THz gyrotrons as per the use in various scientific and technological applications is also discussed. [ABSTRACT FROM AUTHOR]