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A nonlinear lumped element transmission line (NLETL) with linear inductors and using capacitors as nonlinear elements was built to operate as a high voltage pulse sharpener. NLETLS are suitable for use in fast sampling pulse generation circuits and in the formation of high-voltage solitons, among other applications. In this paper, a NLETL built with 30 sections was tested up to 500 V providing a pulse...
Low loss dielectric materials with high permittivity and nonlinear behavior are essential for use in capacitive non linear transmission lines (NLTLs) for RF generation. NLTLs have a great potential to generate solitons waves for high power microwave applications in mobile defense platforms and satellite communications. In this work the dielectric properties of a piezoelectric capacitor based on lead-zirconate-titanate...
The present report examines both analytically and numerically by using a two-dimensional electromagnetic solver the frequency tuning characteristics and electric-field patterns in a two-celled system consisting of cylindrical cavities coupled by a circular iris. It is shown that the presence of the iris introduces unique features not found in hollow circular cavities, namely, the occurrence of flat...
The main purpose of this work was to measure the resonant frequency and the Q-factor for the niobium superconducting reentrant cavities to be used in parametric transducers of the gravitational wave detector Mario Schenberg. Many cavities were manufactured from niobium with high tantalum impurities (1420 ppm) and they were cryogenically tested to determine their resonance frequencies and unloaded...
The present report branches out into two related topics. The first is concerned with the implementation of a computational modeling to predict the behavior of electromagnetic materials in confined environment by using electromagnetic three-dimensional simulation. The second topic re-examines the Nicolson-Ross-Weir mathematical model to retrieve the constitutive parameters (complex permittivity and...
A comparative study is given on the bunching mechanisms which develops in transit-time tubes with RF-field bunching, often referred to as monotrons. Uniform and stepped wise longitudinal electric-field profiles are discussed, and it is shown that the two-fold enhancement in the conversion efficiency of a monotron operating in the ?? mode-instead of the longitudinally uniform TM010 mode for which the...
Microwave propagation in a metallic waveguide loaded with an array of split-ring resonators is examined both analytically and experimentally. The synthesized combined medium exhibits a frequency band around 6.0 GHz with simultaneously negative values of permittivity and permeability which allow transmission in an otherwise forbidden band for the hollow waveguide.
This article overviews recent activities carried out in the construction and tests of a 10 kW, 6.7 GHz monotron. In addition to the monotron components- injection electron gun, cavity resonator, and output waveguide-, a hard-tube pulser with three tretrodes in parallel and able to produce negative voltages up to 30 kV/20 A from a positive DC charging power supply is also discussed.
In its classical embodiment, the monotron has its conversion efficiency limited to 20.0%. But we demonstrate here that on considering a stepped electric-field axial profile the monotron efficiency can attain the theoretical maximum value of 57.0%, almost three times as high as that obtained from the conventional uniform field distribution. This is accomplished by using two cavities electromagnetically...
The two-fold enhancement in the conversion efficiency of a monotron operating in the pi mode-instead of the TM010 mode for which the efficiency is limited to 20 percent-arises from a phase synchronization process due the action of RF electric fields of reversed signs in each partition of the bisected cavity.
It is examined a vircator with a circular cavity placed transversally in a cylindrical waveguide driven by two counter-streaming electron beams. Results from three-dimensional particle-in-cell (PIC) simulations show a conversion efficiency of 32.0%.
Including a coaxial circular insert separated by a gap spacing from the cavity end, reentrant cavities with dimensions conveniently small can operate at large wavelengths, thereby finding direct application in klystron cavities for low frequencies. It is illustrated that a reentrant cavity 8.0 cm in diameter, loaded with a coaxial insert of radius 2.0 cm and a 2.0 mm gap spacing, resonates at a 30...
A coaxial line periodically loaded by circular disks on the inner conductor is designed to act as Bragg reflector in the 4.0-10.0 GHz frequency range. This is achieved by placing 10 disks (0.35 cm thick and 6.22 cm in diameter) equally spaced by the periodic distance of 1.8 cm on a coaxial waveguide with inner and outer diameters of 6.90 cm and 4.22 cm. Analytical discussion followed by 2D and 3D...
The filtering characteristics of a coaxial Bragg reflector are studied experimentally. Made from stainless steel, this coaxial Bragg reflector incorporates a cylindrical inner rod with 10 disks 0.35 cm thick and 6.22 cm in diameter equally spaced by the periodic distance of 1.8 cm. Experimental results demonstrate a bandgap of 5.85 GHz centered at the 6.7 GHz design frequency in excellent agreement...
An excitation model for TM-mode cylindrical cavities driven by a modulated electron beam with application in transit-time microwave tubes is developed. It is shown that the slowly time varying amplitude of the self-sustained oscillations is described by a reduced form of the classical van der Pol equation. Encompassing the relevant parameters of the dynamics of the rf field-electron beam interaction...
We describe the construction and emission tests of an electron gun used to accelerate and inject a hollow electron beam into a cylindrical cavity to produce high-power microwaves at 6.7 GHz, a frequency suitable for communications, medical and industrial applications. In addition to the monotron components, a hard-tube pulser with three tetrodes in parallel is also discussed, able to generate negative...
It is examined how the resonance frequency and the electrical Q factor relate to the geometrical shape of the coaxial insert in reentrant klystron cavities. Through proper selection of the geometry of the coaxial inner conductor (either circular cylinders or truncated cones), a tuning coefficient of 25.0 MHz/mum can be obtained at resonance frequencies around 1.0 GHz with cylindrical cavities of 8...
Summary form only given. In this paper, we will show the SPICE simulation results compared to the experimental data obtained with a 10kV/5A HT modulator, which uses one tetrode tube and a series IGBT transistor (IRGB420U) as a control switch for frequency repetition of the order of 100 Hz and pulse duration of 20-60 mus.
Summary form only given. Much emphasis has been placed on microwave generators that do not require an external magnetic field so as to reduce cost, size and weight of the device. One such device is the monotron, which is a self-excited oscillator consisting of an electron team that transits across a resonant cavity, which plays the part of an ordinary LCR oscillating tank circuit. The monotron lumped...
In general, high voltage (HV) power modulators use vacuum tube (tetrode) operating as an on-off switch to discharge a capacitor bank through the load. To ease pulser construction a special circuit layout with tube cathode near ground is used, whose switching control is made by a solid-state switch in series with the cathode electrode. This avoids isolation problems between tetrode deck and grounded...
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