Power Microwave Pulses Research Articles

Генерация последовательности мощных ультракоротких микроволновых импульсов на основе эффекта сверхизлучения релятивистской лампы обратной волны с отражателями на концах пространства взаимодействия

In a non-stationary numerical experiment, it is shown that introducing the reflections at the ends of the slow wave structure of a relativistic backward-wave oscillator operating in the superradiance mode provides the conditions for the formation of a sequence powerful ultrashort microwave pulses during a single pulse of the current. The conversion factor, defined as the ratio of the peak power of an ultrashort pulse to the power of an electron beam, is about 3 for the first (main) pulse and decreases to ≈ 2 for subsequent pulses

Photonic generation of pulsed microwave signals in the X-, Ku- and K-band.

Photonic microwave generation of high-power pulsed signals in the X-, Ku- and K-band using charge-compensated MUTC photodiodes is demonstrated. The impulse photoresponse without modulation showed a maximum peak voltage of 38.3 V and full-width at half-maximum of 30 ps. High power pulsed microwave signals at 10, 17 and 22 GHz with peak power up to 44.2 dBm (26.3 W), 41.6 dBm (14.5 W) and 40.6 dBm (11.5 W) were achieved, respectively.

Wake excitation by a powerful microwave pulse and its evolution in a plasma-filled waveguide

We present the results of an experimental, theoretical, and numerical study of short and long time wake, produced by a 0.6 ns, 0.5 GW, 9.6 GHz high power microwave (HPM) pulse propagating in a plasma-filled cylindrical waveguide. The perturbation of the plasma density caused by the ponderomotive force prevents not only the pulse from spreading due to dispersion, but also leads to pulse compression. The high power pulse leaves far behind it a long lived positively-charged plasma whose electrons oscillate in the Coulomb potential well and ionize the background neutral gas over several tens to hundreds of nanoseconds. This leads to long time light emission observed in the experiment. The density of this newly created plasma can exceed many-folds its initial value. The theoretical model shows that as a result of the wake excitation by the propagating HPM pulse, fast electrons are ejected and collected on the waveguide wall. These high energy electrons, pulse compression, and long time light emission are evidence of the wake formation. The results of the experiment, the analytical model, and the numerical simulations are in good agreement.

Effects of Diffraction, Dispersion, and Absorption of Electromagnetic Waves in the Diagnostics of High-Power Microwave Pulses Using Wide-Aperture Liquid Calorimeters

Using a simple theory and finite-difference time domain (FDTD) simulations involving the Lorentz model, we demonstrate some problems in the determination of pulse waveform, amplitude, and peak power of high-power microwave pulses, when performed together with calorimetric measurement of the pulse energy, arising from the wave diffraction as well as from its dispersion in the absorbing liquid. Considering few typical pulse shapes and other experimental conditions, we outline the general limitations and recommendations for performing such measurements.

Repeated exposure to nanosecond high power pulsed microwaves increases cancer incidence in rat.

High-power microwaves are used to inhibit electronics of threatening military or civilian vehicles. This work aims to assess health hazards of high-power microwaves and helps to define hazard threshold levels of modulated radiofrequency exposures such as those emitted by the first generations of mobile phones. Rats were exposed to the highest possible field levels, under single acute or repetitive exposures for eight weeks. Intense microwave electric fields at 1 MV m-1 of nanoseconds duration were applied from two sources at different carrier frequencies of 10 and 3.7 GHz. The repetition rate was 100 pps, and the duration of train pulses lasted from 10 s to twice 8 min. The effects on the central nervous system were evaluated, by labelling brain inflammation marker GFAP and by performing different behavioural tests: rotarod, T-maze, beam-walking, open-field, and avoidance test. Long-time survival was measured in animals repeatedly exposed, and anatomopathological analysis was performed on animals sacrificed at two years of life or earlier in case of precocious death. Control groups were sham exposed. Few effects were observed on behaviour. With acute exposure, an avoidance reflex was shown at very high thermal level (22 W kg-1); GFAP was increased some days after exposure. Most importantly, with repeated exposures, survival time was 4-months shorter in the exposed group, with eleven animals exhibiting a large sub-cutaneous tumour, compared to two in the sham group. A residual X-ray exposure was also present in the beam (0.8 Gy), which is probably not a bias for the observed result. High power microwaves below thermal level in average, can increase cancer prevalence and decrease survival time in rats, without clear effects on behaviour. The parameters of this effect need to be further explored, and a more precise dosimetry to be performed.

The Magnetron Synchronization Band

The magnetron synchronization band is measured. For measurements, a microwave generator based on a magnetron of a household oven with a wide range of changes in pulsed and average microwave power was used. Synchronization in a specified band is shown to require an order of magnitude lower microwave power than follows from recent publications. A method for measuring the resonator parameters at a large coefficient of coupling with the line is presented.

Полоса синхронизации магнетрона

Frequency bandwidth of the injection locked magnetron by an external microwave signal was measured. It is shown that injection locking in a given band requires an order of magnitude less microwave power than follows from recent works. For measurements, a microwave generator based on a magnetron of a household oven with a wide range of changes in pulsed and average microwave power was used. A method for measuring the parameters of strongly coupled resonators is given.

Kinetic simulation of the transition from a pulse-modulation microwave discharge to a continuous plasma

The generation of a very strong peak current in the first period (PCFP) in a pulse-modulated microwave discharge has been discussed in previous studies. In this paper we focus on the transition process from a pulsed discharge to a fully continuous one driven by the pulsed microwave power source by means of a kinetic model. The computational results show that by increasing the duty cycle or voltage modulation rate (VMR), the discharge eventually becomes fully continuous and PCFP can no longer be observed. In the transition process, the distributions of the electric field, electron energy probability function (EEPF) and plasma density are discussed according to the simulation data, showing different discharge structures. The simulations indicate that many high-energy electrons with electron energy larger than 20 eV and low-energy electrons with electron energy less than 3 eV could be generated in a pulsed microwave discharge, together with a reversal electric field formed in the anode sheath when PCFP occurs. However, only medium-energy electrons could be observed in a fully continuous discharge. Therefore, by investigating the transition process the pulse-modulated microwave discharges can be further optimized for plasma applications at atmospheric pressure.

Effect of innovative microwave assisted freezing (MAF) on the quality attributes of apples and potatoes

This study considered the effect of low energy microwave assisted freezing (MAF) on freezing time and quality attributes (microstructure, texture, drip loss and colour) of apple and potato. MAF of apples and potatoes was performed by applying constant microwave (MW) power (167 W/kg) and pulsed MW power (500 and 667 W/kg with 10 s pulse width and 20 s pulse interval resulting in an average power of 167 and 222 W/kg) during the freezing process. The temperature profile was monitored during the freezing process, and the microstructure was examined using X-ray micro-tomography and cryo-SEM. Other quality parameters such as texture, drip loss and colour were evaluated with thawed samples. It appeared that the freezing time was not affected by the MAF process. It is the first time that a MAF process is used for freezing plant-based products and showed that the application of microwaves during freezing process caused less freeze damage than the control condition.

Research on pulse compression energy extraction technology based on X-band energy storage switching method.

A high power microwave source based on energy storage switching pulse compression technology can produce a high power microwave pulse with good repeatability and frequency stability for a long time and has a good development prospect. In order to improve the power gain, this paper studies the working characteristics of the energy extraction structure of the X-band energy storage switching pulse compression device. The theoretical analysis results show that the impedance mismatch exists in the traditional energy extraction structure after the pulse compression is transferred to the energy extraction stage and the energy extraction efficiency is not high, which results in the power gain limitation. Therefore, through theoretical calculation and simulation, an improved scheme based on output inductance diaphragm is proposed in this paper. The scheme has high power capacity and can achieve impedance matching without changing the resonant frequency of the energy storage cavity, so as to improve the power gain of the pulse compression device. The high power experimental results show that the power gain of the pulse compression device can be increased from 6.24 times to 7.22 times and the energy extraction efficiency can be increased by 17.5% by placing 17 mm slot spacing inductance diaphragm at 45 mm of the H-T arm of the waveguide, which verifies the feasibility of the improved scheme.

Implementation of High Power Microwave Pulse Compressor

High-frequency power amplifiers can be equipped with complementary pulse-compressor systems to fulfill the advanced cavity power requirements. Microwave pulse compression is a power extraction method based on pulsewidth reduction and electronic triggering. The cavity is fed by pulsed-RF source, the resonance is evolved at $t\geq t_{0}$ , $t_{0}=\textrm {cavity}$ filling time. Established standing waves or resonance condition is brokendown by triggered plasma switch programmed with adjustable delay and pulsewidth. This causes the stored energy to be transmitted as shorter output RF-pulse. The implementation of a microwave pulse compression system requires careful measurements and structural modifications to be able to tune design parameters for optimal setup. In the scope of this paper, the experimental results are obtained for different waveguide lengths and various load configurations (to exploit new opportunities). All connections, iris configuration, and precise adjustment of plasma triggering have been set up cautiously. The cavity gain is increased up to 23 dB with trigatron driving improvements. High power requirements and demands are investigated for many applications, particularly for biomedical science projects.

Reprint of: Sterilization of small vial using electron cyclotron resonance plasma

The sterilization of a small vial using electron cyclotron resonance (ECR) plasma was investigated. The ECR plasma was generated throughout the inside of the small vial, which was sealed with nonwoven fabric, by using magnetic configuration in which the ECR point was located inside the small vial. Moreover, it was demonstrated that the temperature of the small vial was finely controlled by the pulse width and pulse frequency of the pulsed microwave power. A biological indicator (BI), Geobacillus Stearothermophilus, containing 1 × 105 spores present inside the small vial was successfully inactivated in a total treatment time of about 14 min while maintaining treatment temperature of less than 65 °C.

Experimental Study of Multipoint Ignition in Methane–Air Mixtures by Pulsed Microwave Power

Microwave plasma offers a promising method to achieve faster combustion in internal combustion engine. In this paper, microwave multipoint ignition was confirmed via the high-speed imaging technique. The experiment was conducted with microwave resonant ignition system and optical system. A 2-ms, 3000-W, 2.45-GHz pulsed microwave power was used as energy source to produce initial flame kernel in combustion chamber. High-speed imaging was used to record the ignition characteristics via high-speed camera. Ignition experiments were conducted at high pressure of 2 bars of stoichiometric methane–air mixtures. It can be observed in the image and the pressure curves that multiple flame kernels are generated simultaneously. Faster combustion speed is achieved by pulsed microwave power ignition than traditional spark plug ignition in constant volume chamber.

Global model for high power microwave pulse breakdown in air and SF6

The breakdown in air and SF6 caused by a high power microwave pulse is investigated using a global model, respectively, in which the rate coefficients such as an ionization rate derived from the Boltzmann equation solver BOLSIG+ are adopted. The breakdown prediction from the global model agrees very well with experimental data. The relation curves among the effective breakdown threshold, pressure, and total duration of pulse with either different frequencies or different duration of pulse are nearly the same, but change with the background gas species. At atmospheric pressure, the breakdown threshold of SF6 for a long microwave pulse is about three times larger than that of air. However, the ratio decreases, when the gas pressure or the total duration of pulse is decreased.

Sterilization of small vial using electron cyclotron resonance plasma

The sterilization of a small vial using electron cyclotron resonance (ECR) plasma was investigated. The ECR plasma was generated throughout the inside of the small vial, which was sealed with nonwoven fabric, by using magnetic configuration in which the ECR point was located inside the small vial. Moreover, it was demonstrated that the temperature of the small vial was finely controlled by the pulse width and pulse frequency of the pulsed microwave power. A biological indicator (BI), Geobacillus Stearothermophilus, containing 1 × 105 spores present inside the small vial was successfully inactivated in a total treatment time of about 14 min while maintaining treatment temperature of less than 65 °C.

VIRCATOR - ANALYTICAL AND NUMERICAL ANALYSIS AND OPTIMIZATION OF A VACUUM MICROWAVE HIGH POWER DEVICE

Vircator is a vacuum microwave device characterised by a pulse working signal and high power. It is classified as a High-Power Microwave (HPM) device and often is a component of Electromagnetic Pulse (EMP) weapons and microwave power transmissions. The direct source of a microwave signal is an oscillation of the so-called virtual cathode. The goal of the presented research was to apply analytical analysis and numerical prototyping methods as a methodology for optimization of the electrical and mechanical design taking into account transformation of electrons' energy into a microwave signal. One of the key drawbacks of viractors as a microwave source is a low energy efficiency transformation, which is typically of a single percentage.

Generation of powerful microwave pulses by channel power summation of two X-band phase-locked relativistic backward wave oscillators

We demonstrate both theoretically and experimentally the possibility of the generation of powerful microwave pulses by channel power summation of two X-band phase-locked relativistic backward wave oscillators (RBWOs). A modulated electron beam induced by an external signal can lead the microwave field with an arbitrary initial phase to the same equilibrium phase, which is determined by the initial phase of the external signal. A high-current dual-beam accelerator was built to drive the two RBWOs. An external signal was divided into two channels with an adjusted relative phase and injected into the two RBWOs through two TE10-TEM mode converters. The generated microwaves were combined with a power combiner consisting of two TM01-TE11 serpentine mode converters with a common output. In the experiments, as the input power for each channel was 150 kW, the two RBWOs output 3.1 GW and 3.7 GW, respectively, the jitter of the relative phase of two output microwaves was about 20°, and the summation power from the power combiner is 6.2 GW, corresponding to a combination efficiency of 91%.

Extremely High Peak Power Obtained at 29 GHZ Microwave Pulse Generation

The paper presents research results on enhancing the peak power of microwave pulses with sub- and nanosecond length using a backward-wave oscillator (BWO) operating at 29 GHz frequency and possessing a reproducible phase structure. Experiments are conducted in two modes on a high-current electron accelerator with the required electron beam power. In the first (superradiation) mode, which utilizes the elongated slow-wave structure, the BWO peak power is 3 GW at 180 ns pulse duration (full width at halfmaximum, FWHM). In the second (quasi-stationary) mode, the BWO peak power reaches 600 MW at ~2 ns pulse duration (FWHM). The phase spread from pulse to pulse can vary from units to several tens of percent in a nanosecond pulse mode. The experiments do not show any influence of microwave breakdown on the BWO power generation and radiation pulse duration.

Study of microwave damage effect on HEMT low noise amplifier under different drain voltage bias

The microwave damage effect on high electron mobility transistor (HEMT) low noise amplifier (LNA) under different drain voltage bias is studied using TCAD simulation and experiments. Simulation and experimental results suggest that the damage power thresholds and damage locations of single stage LNA under different drain voltage bias are almost the same. Nevertheless, the output power under zero drain bias is about 5.6dB higher than it under normal (3V) drain bias with the injection of large power microwave pulses. In Addition, the output power relative to it under normal drain bias decreases linearly with the increase of drain bias, following the function of PdB=−1.85Vds+5.7. For multi-stage LNA, the observation using optical microscope reveals that the first and second stage HEMT of LNA under zero drain bias are both damaged while only first stage HEMT of LNA under normal bias is damaged with the injection of same large power microwave pulses, which is consistent with simulated output characteristics results.

Subthreshold self-sustained discharge initiated by a microwave beam in a large volume of high-pressure gas

The presented results are based on the experimental studies of generating a long plasma column in gas (or gas mixtures) at atmospheric pressure both in free space and in a closed chamber. The microwave generator GYROTRON was used as an energy source. Its parameters were as follows: the microwave pulse power was in the range of 200 ≤ P ≤ 600 kW, the wavelength was λ ≈ 0.4 cm, and the pulse duration was in the range of 0.5 ≤ τi ≤ 20 ms. Under strong subthreshold conditions, a plasma column with a length of up to L ≤ 50 cm was created using a microwave beam that was formed using a quasi-optical mirror system. The discharge initiation system had an original design. Based on the discharge structure, expansion dynamics and typical discharge plasma parameters, this discharge can be attributed to the type of microwave discharges that are known as self/non-self-sustained discharges. The discharge properties and advantages of using this discharge as a basis of a plasma-chemical reactor are discussed.