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The paper show the multipaction capability of Thales RF output solutions for today high power L- and S-Band TWTs. Thales accepts that a real prediction of the multipaction onset level of complex coaxial structures like in example a TNC connector, with dielectrics, air gaps and complex electric fields inside, is not possible with today knowledge. Therefore Thales prefers to qualify their RF output...
MILO has been analyzed for its beam wave interaction and the RF released energy has been calculated. The analytical results are obtained, typically, for a S-band MILO, and released RF energy is found as 2.5 Joule at 300 kV applied voltage. The analytical results has also been validated through PIC simulation code MAGIC and found to be in close agreement.
We report experiments and analysis of field emission from metallic knife-edge cathodes coated with thin film Lanthanum Hexaboride (LaB6), a low work function material (~2.5 eV). The emission current density is found to depend sensitively on film properties, particularly the thickness of the LaB6 layer. Films thinner than approximately 10 nm greatly enhance the emitted current. However, cathodes coated...
In this work, we present a comparison between plasma reduction factors for the case of a pencil e-beam inside a hollow metallic pipe. The values under comparison were obtained via analytic expressions given in the literature and the result of a 1D large signal time domain code. The main distinctive feature of this analysis is the additional consideration of dc space charge forces, since the actual...
One-dimensional (1D) periodic structures with a localized defect and operating in the mm and sub-mm wavelength ranges can be formed by machining small perturbations on the waveguide's walls. We demonstrate the applicability of such structures for diverse applications: from particle acceleration to materials research. It is shown that the strong field enhancement inside the sizable lattice defect should...
A useful design technique of helix pitch profile for high-efficiency Traveling-Wave tubes (TWTs) is put forward. The purpose of the design technique is to increase the normalized axial growth rate of ac electric field amplitude by selecting an appropriate helix pitch profile and so that the power and efficiency are maximized.
In high-power microwave diode design, the space-charge-limited current is important because of its relation to the diode impedance, and the formation of the virtual cathode. Although the Langmuir-Blodgett law, as a numerical solution, is helpful, a simple functional expression would be more convenient for practical research and the divergence of the series for large Rc/Ra would be avoided. First principle...
In this paper, the interaction section consisted of the open spherical resonator is designed, and a W-band gyroklystron with the open spherical resonators has been simulated with the MAGIC simulation software. The results of simulations show that the gyroklystron with the spherical resonators operates stably in the operating mode TE102 and no competing modes caused. The output power of about 50 kW...
This paper presents electromagnetic and thermal simulation of a 250 kW 350 MHz balanced choke type coaxial RF window including T-bar transition using CST Microwave Studio and ANSYS. The S-parameter analysis of the coaxial widow, using 3D Microwave Studio, has revealed that a match can be found at any frequency between 300 MHz and 1 GHz by suitably tailoring the choke depth independently. Sensitivity...
In order to exploit the cavity resonance effect for enhancing the power conversion efficiency of coaxial vircators, a modification in the drift region is proposed. The modification introduces geometrical parameters which can be varied to change the structure and strength of modes inside the vircator. These cavity parameters have been optimized using particle-in-cell (PIC) simulation to increase the...
For the analysis of CNT based field emitters a precise calculation of effective emission area is quite important. However, its calculation still involves a lot of uncertainty. Some work was done towards calculating the effective emission area by simulating a single tip CNT cathode using CST Particle Studio. In the model developed, the hemispherical CNT tip was divided into several areas. Electron...
This paper describes the design and experimentation of electrostatic focusing of electron beam using a demountable vacuum measurement setup. Initially a focusing setup is designed for focusing a single on-axis low perveance beam. The design was carried out using an in house developed 2.5 D finite difference electron optics code PIERCE and CST Particle Studio. This focusing scheme is being extended...
A new geometry of a matched termination using lossy dielectric materials for an overmoded cylindrical waveguide is explored in this present work. The matched termination is designed based on attenuating the microwave using lossy dielectric materials or resistive materials by numerical simulation. The geometry is optimized such that it can be used for a cylindrical waveguide operating on fundamental...
We discuss the design and implementation of a waveguide coupler for a sheet-beam coupled-cavity structure. Discussion includes excitation of the fundamental mode with low VSWR, wide bandwidth, circuit sensitivity, and tuning. We conclude with a comparison with round-beam structure, and experimental results of sheet beam coupler.
Plasma assisted devices are unique source for microwave radiation. This paper presents the simulation results of beam-wave interaction in rippled waveguide SWS for plasma assisted BWO.
An equivalent circuit analysis of a plasma-filled helical slow-wave structure immersed in a strong longitudinal magnetic field was developed to analyze the dispersion characteristics of the structure. The analysis predicted the formation of hybrid-plasma slow waves in the structure and the enhancement of longitudinal electric field inside the helix for facilitating strong beam-wave interaction in...
In this paper, a two-section folded waveguide of Terahertz (THz) extended interaction oscillator (EIO) is presented, which is studied by the help of particle-in-cell (PIC) simulation. The output power and operation frequency are studied.
Cylindrical coaxial cavity resonator with shift-tubes coupled with rectangular waveguide is designed. The gap characteristic impedance and external quality factor of higher order transverse magnetic mode TM310 in the cavity are simulated with high frequency electromagnetic simulator ISFEL-3D. The ununiformity of the characteristic impedance resulted from the coupling aperture is reduced through introduction...
Parasitic mode suppression was studied by the electromagnetic theory. The method of increasing the frequency interval (FI) between operating mode and parasitic mode was proposed to suppress the unwanted mode. In order to increase FI, a pair of metal rings (MR) is installed in the coaxial resonator operating at high-order-mode for multi-beam klystron (MBK). A TM310 mode coaxial resonator has been manufactured...
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