Switching speed effect of phase shift keying in SLED for generating high power microwaves

SLAC energy doubler （SLED） type radio-frequency pulse compressors are widely used in large-scale particle accelerators for converting long-duration moderate-power input pulses into short-duration high-power output pulses. Phase shift keying （PSK） is one of the key components in SLED pulse compression systems. Performance of the PSK will influence the output characteristics of the SLED, such as the rise-time of the output pulse, maximal peak power gain, and energy efficiency. In this paper, a high power microwave source based on power combining and pulse compression of conventional klystrons is introduced. The effects of nonideal PSK with slow switching speed and PSK without power output during the switching process are investigated, and the experimental results with nonideal PSK agree well with the analytical results.

Review of high-power pulsed systems at the Institute of High Current Electronics

In this paper,we give a review of some most powerful pulsed systems developed at the Institute of High Current Electronics(HCEI),Siberian Branch,Russian Academy of Sciences,and describe latest achievements of the teams dealing with these installations.Besides the presented high-power systems,HCEI performs numerous investigations using much less powerful generators.For instance,last year much attention was paying to the research and development of the intense low-energy(<200 kV)high-current electron and ion beam and plasma sources,and their application in the technology[1-3].

Simulation and experimental study of high power microwave damage effect on AlGaAs/InGaAs pseudomorphic high electron mobility transistor

The high power microwave （HPM） damage effect on the AIGaAs/InGaAs pseudomorphic high electron mobility transistor （pHEMT） is studied by simulation and experiments. Simulated results suggest that the HPM damage to pHEMT is due to device burn-out caused by the emerging current path and strong electric field beneath the gate. Besides, the results demonstrate that the damage power threshold decreases but the energy threshold slightly increases with the increase of pulse-width, indicating that HPM with longer pulse-width requires lower power density but more energy to cause the damage to pHEMT. The empirical formulas are proposed to describe the pulse-width dependence. Then the experimental data validate the pulse-width dependence and verify that the proposed formula P = 55τ^-0.06 is capable of quickly and accurately estimating the HPM damage susceptibility of pHEMT. Finally the interior observation of damaged samples by scanning electron microscopy （SEM） illustrates that the failure mechanism of the HPM damage to pHEMT is indeed device bum-out and the location beneath the gate near the source side is most susceptible to bum-out, which is in accordance with the simulated results.

Damage effect and mechanism of the GaAs high electron mobility transistor induced by high power microwave

In this paper, we present the damage effect and mechanism of high power microwave （HPM） on AIGaAs/GaAs pseudomorphic high-electron-mobility transistor （pHEMT） of low-noise amplifier （LNA）. A detailed investigation is carried out by simulation and experiment study. A two-dimensional electro-thermal model of the typical GaAs pHEMT induced by HPM is established in this paper. The simulation result reveals that avalanche breakdown, intrinsic excitation, and thermal breakdown all contribute to damage process. Heat accumulation occurs during the positive half cycle and the cylinder under the gate near the source side is most susceptible to burn-out. Experiment is carried out by injecting high power microwave into GaAs pHEMT LNA samples. It is found that the damage to LNA is because of the burn-out at first stage pHEMT. The interiors of the damaged samples are observed by scanning electron microscopy （SEM） and energy dispersive spectrometer （EDS）. Experimental results accord well with the simulation of our model.

Study on the Generation of Ultra-Wideband (UWB) High Power Microwave

The experimental study of ultra-wideband (UWB) technology, its generation and on-line measurement are presented. An experimental repetitive UWB system is designed, manufactured, and tested. High-pressure spark gap switch and its components, as well as oil spark gap switch are studied experimentally on the system. Experimental results indicate that the system operates at a 200 pps repetitive rate with a stable performance. 100 MW peak power UWB pulses are obtained on the system. Fast-time response capacitive divider is designed and fabricated, allowing for an accurate measurement of the high power UWB signal. The main issues related to the design of the switch and the UWB signal online measurement are discussed.

Changes in Rat Testicular Germ Cell Apoptosis after High Power Microwave Radiation

Aim:To study the effect of high power microwave (HPM) radiation on the testicular germ cell apoptosis. Methods: One hundred and twenty-five Spraque-Dawley rats were randomly divided into two groups, the control group and the experimental group and the latter was further divided into four subgroups: 10 mW/cm2 5 min, 10 mW/cm210 min, 20 mw/cm2 5 min and 20 mW/cm210 min. The experimental groups were radiated with S wave band of 10 mW/ cm2,20 mW/cm2 high power microwave for 5 or 10 min. Testicular samples were taken at 6 h, 24 h, 48 h, 72 h and 5 d after radiation. The testicular germ cell apoptosis was detected by in situ terminal deoxynucleotityl transferase mediated dUTP nick end labeling (TUNEL). Results: The number of apoptotic cells of the 6 h, 24 h and 48 h experimental groups after 10 and 20 mW/cm2 radiation for 5 min was significantly larger than that of the controls (P< 0.01), especially after 10 mW/cm2 radiation. The number of the 6 h group reached the peak (161.27±+5.90)/5 convoluted tubules. The changes in the other experimental groups had no significant difference compared with the controls (P>0.05). Conclusion: HPM increases the germ cell apoptosis of rat testis, which is related to the time of radiation and sample acquisition. In the condition of the present test, 5 minutes of HPM radiation may significantly enhance testicular germ cell apoptosis and damage, which in turn may influence the reproductive function of the rats.

20-Hydroxyecdysone Improves Neuronal Differentiation of Adult Hippocampal Neural Stem Cells in High Power Microwave Radiation-Exposed Rats

Objective The hippocampus is thought to be a vulnerable target of microwave exposure.The aim of the present study was to investigate whether 20-hydroxyecdysone(20E)acted as a fate regulator of adult rat hippocampal neural stem cells(NSCs).Furthermore,we investigated if 20E attenuated high power microwave(HMP)radiation-induced learning and memory deficits.Methods Sixty male Sprague-Dawley rats were randomly divided into three groups:normal controls,radiation treated,and radiation+20E treated.Rats in the radiation and radiation+20E treatment groups were exposed to HPM radiation from a microwave emission system.The learning and memory abilities of the rats were assessed using the Morris water maze test.Primary adult rat hippocampal NSCs were isolated in vitro and cultured to evaluate their proliferation and differentiation.In addition,hematoxylin&eosin staining,western blotting,and immunofluorescence were used to detect changes in the rat brain and the proliferation and differentiation of the adult rat hippocampal NSCs after HPM radiation exposure.Results The results showed that 20E induced neuronal differentiation of adult hippocampal NSCs from HPM radiation-exposed rats via the Wnt3a/β-catenin signaling pathway in vitro.Furthermore,20E facilitated neurogenesis in the subgranular zone of the rat brain following HPM radiation exposure.Administration of 20E attenuated learning and memory deficits in HPM radiation-exposed rats and frizzled-related protein(FRZB)reduced the 20E-induced nuclear translocation ofβ-catenin,while FRZB treatment also reversed 20E-induced neuronal differentiation of NSCs in vitro.Conclusion These results suggested that 20E was a fate regulator of adult rat hippocampal NSCs,where it played a role in attenuating HPM radiation-induced learning and memory deficits.

C band microwave damage characteristics of pseudomorphic high electron mobility transistor

The damage effect characteristics of GaAs pseudomorphic high electron mobility transistor(pHEMT)under the irradiation of C band high-power microwave(HPM)is investigated in this paper.Based on the theoretical analysis,the thermoelectric coupling model is established,and the key damage parameters of the device under typical pulse conditions are predicted,including the damage location,damage power,etc.By the injection effect test and device microanatomy analysis through using scanning electron microscope(SEM)and energy dispersive spectrometer(EDS),it is concluded that the gate metal in the first stage of the device is the vulnerable to HPM damage,especially the side below the gate near the source.The damage power in the injection test is about 40 dBm and in good agreement with the simulation result.This work has a certain reference value for microwave damage assessment of pHEMT.

Temperature dependence of latch-up effects in CMOS inverter induced by high power microwave

The temperature dependence of the latch-up effects in a CMOS inverter based on 0.5 μm technology caused by high power microwave （HPM） is studied. The malfunction and power supply current characteristics are revealed and adopted as the latch-up criteria. The thermal effect is shown and analyzed in detail. CMOS in- verters operating at high ambient temperature are confirmed to be more susceptible to HPM, which is verified by experimental results from previous literature. Besides the dependence of the latch-up triggering power P on the ambient temperature T follows the power-law equation P = ATβ. Meanwhile, the ever reported latch-up delay time characteristic is interpreted to be affected by the temperature distribution. In addition, it is found that the power threshold increases with the decrease in pulse width but the degree of change with a certain pulse width is constant at different ambient temperatures. Also, the energy absorbed to cause latch-up at a certain temperature is basically sustained at a constant value.

Effects of microwave pulse-width damage on a bipolar transistor

This paper presents a theoretical study of the pulse-width effects on the damage process of a typical bipolar transistor caused by high power microwaves（HPMs） through the injection approach.The dependences of the microwave damage power,P,and the absorbed energy,E,required to cause the device failure on the pulse width τ are obtained in the nanosecond region by utilizing the curve fitting method.A comparison of the microwave pulse damage data and the existing dc pulse damage data for the same transistor is carried out.By means of a two-dimensional simulator,ISE-TCAD,the internal damage processes of the device caused by microwave voltage signals and dc pulse voltage signals are analyzed comparatively.The simulation results suggest that the temperature-rising positions of the device induced by the microwaves in the negative and positive half periods are different,while only one hot spot exists under the injection of dc pulses.The results demonstrate that the microwave damage power threshold and the absorbed energy must exceed the dc pulse power threshold and the absorbed energy,respectively.The dc pulse damage data may be useful as a lower bound for microwave pulse damage data.

PIC-MCC Simulation for HPM Multipactor Discharge on Dielectric Surface in Vacuum

In order to understand the physical mechanism of multipactor discharge on dielectric window surface under high power microwave （HPM） excitation in vacuum, an electron movement simulation model based on the particle-in-cell （PIC） Monte Carlo （MC） is built in this paper. The influences of microwave electromagnetic field and electrostatic field from dielectric surface charging are simultaneously considered in this model. During the simulation, the emission velocity and angle distribution of secondary electrons from the dielectric surface are taken into account. The movement trajectories of electron clusters under complex field excitation are obtained. The influences of emergence angle and microwave electromagnetic parameters on the electron movement are analyzed. It is found that the emergence angle of electrons from the surface has significant effect on its movement, and both the impact energy and return time of electrons oscillate periodically with the phase of microwave field. The number of secondary electrons and induced electrostatic field from multipactoring are also investigated. The results reveal that both values oscillate periodically at twice the microwave frequency, which is due to the electron impact energy oscillating with microwave period. A schematic diagram is proposed to explain the periodical oscillation phenomena.

Plasma Limiter Based on Surface Wave Plasma Excited by Microwave

A novel plasma limiter, in which the plasma is excited by surface wave, is presented. The breakdown time of some gases filled in the limiter were calculated as a function of gas pres- sure, ionization degree and density of seed electrons under low pressure （0.01 -1 Torr） and high pressure （10 -1000 Torr） cases. The results show that the limiter filled with Xe with a pressure of 0.9 Torr, seed electron density of 10^16 m^-3, and ionization degree of 10^-4, has a breakdown time of approximate 19.6 ns.

The pulsed microwave damage trend of a bipolar transistor as a function of pulse parameters

In the present paper we conduct a theoretical study of the thermal accumulation effect of a typical bipolar transistor caused by high power pulsed microwaves（HPMs）,and investigate the thermal accumulation effect as a function of pulse repetition frequency（PRF） and duty cycle.A study of the damage mechanism of the device is carried out from the variation analysis of the distribution of the electric field and the current density.The result shows that the accumulation temperature increases with PRF increasing and the threshold for the transistor is about 2 kHz.The response of the peak temperature induced by the injected single pulses indicates that the falling time is much longer than the rising time.Adopting the fitting method,the relationship between the peak temperature and the time during the rising edge and that between the peak temperature and the time during the falling edge are obtained.Moreover,the accumulation temperature decreases with duty cycle increasing for a certain mean power.

Characteristics of Coaxial Vircator in Three Specific Configurations

As a novel vircator device, the coaxial vircator can attain much higher efficiency than the common virtual cathode oscillator. In this paper, coaxial vircators in three specific configurations are studied to describe the efficiency and frequency characteristics and their dependence on geometric parameters. The PIC (Particle in Cell) simulation results show that a power efficiency over 11% can be obtained from the coaxial vircator with a finite inner anode conductor, and a narrow-band output can be achieved. A direct-coupled coaxial vircator has a slightly lower efficiency of about 8%, but in this configuration the efficiency is not strongly dependent on the geometry parameters. The introduction of a reflecting cavity can effectively improve the efficiency under certain parameters. Meanwhile, the research results also indicate that improper cavity parameters will countervail some inherent advantages of the configuration with a finite inner conductor, leading to lower efficiency than that of the direct-coupled one. Meanwhile, an experiment was also carried out to testify the simulation results, and a power efficiency over 3% was obtained from the direct-coupled coaxial vircator.

Magnetically insulated transmission line oscillator oscillated in a modified HEM_(11) mode

This paper puts forward a novel magnetically insulated transmission line oscillator （MILO） for the first time which takes a modified HEM11 mode as its main interaction mode. The excitation of the oscillation mode is made possible by carefully adjusting the arrangements of each resonant cavity in a two-dimensional （2-D） slow wave structure. The high frequency characteristics are analyzed and a PIC simulation is carried out; the detailed results are discussed to get a better understanding of this new MILO. Employing an electron beam of about 441 kV and 39.7 kA, it finds that the modified HEM11 mode MILO generates a high power microwave output of about 1.47 GW at 1.45 GHz. The power conversion efficiency is about 8.4% and the generated microwave is in a TEll-like circularly polarized mode; its polarization direction is decided by the rotation direction of the SWS.

Mode control in a high gain relativistic klystron amplifier with3 GW output power

Higher mode excitation is very serious in the relativistic klystron amplifier, especially for the high gain relativistic amplifier working at tens of kilo-amperes. The mechanism of higher mode excitation is explored in the FIC simulation and it is shown that insufficient separation of adjacent cavities is the main cause of higher mode excitation. So RF lossy material mounted on the drift tube wall is adopted to suppress higher mode excitation. A high gain S-band relativistic klystron amplifier is designed for the beam current of 13 kA and the voltage of 1 MV. PIC simulation shows that the output power is 3.2 GW when the input power is only 2.8 kW.

Modes decomposition in particle-in-cell software CEMPIC

The numerical method of modes analysis and decomposition of the output signal in 3D electromagnetic particle-in-cell simulation is presented. By the method, multiple modes can be resolved at one time using a set of diagnostic data, the amplitudes and the phases of the specified modes can all be given separately. Based on the method, the output signals of one X-band tri-bend mode converter used for one high power microwave device, with ionization process in the device due to the strong normal electric field, are analyzed and decomposed.

HEM_(11) mode magnetically insulated transmission line oscillator:Simulation and experiment

A novel magnetically insulated transmission line oscillator （MILO） in which a modified HEM11 mode is taken as its main interaction mode （HEM11 mode MILO） is simulated and experimented in this paper. The excitation of the oscillation mode is made possible by carefully adjusting the arrangement of each resonant cavity in a two-dimensional slow wave structure. The special feature of such a device is that in the slow-wave-structure region, the interaction mode is HEM11 mode which is a TM-like one that could interact with electron beams effectively; and in the coaxial output region, the microwave mode is TE11 mode which has a favourable field density pattern to be directly radiated. Employing an electron beam of about 441 kV and 39.7 kA, the HEM11 mode MILO generates a high power microwave output of about 1.47 GW at 1.45 GHz in particle-in-cell simulation. The power conversion efficiency is about 8.4 % and the generated microwave is in a TEll-like circular polarization mode. In a preliminary experiment investigation, high power microwave is detected from the device with a frequency of 1.46 GHz, an output energy of 43 J 47 J, and a pulse duration of 44 ns-49 ns when the input voltage is 430 kV450 kV, and the diode current is 37 kA-39 kA.

A compact dual-band radiation system

Complex magnetically insulated transmission line oscillator(MILO),as an important development direction,can enhance the power efficiency and generate dual-band high power microwaves(HPMs).A complex MILO and a preliminary dual-band radiation system have been proposed in our previous studies.However,the axial length of the dual-band radiation system is too long to meet the compact requirements.In this paper,a compact dual-band radiation system is presented and investigated numerically.The compact dual-band radiation system comprises a dual-band cross-shaped mode converter and a dual-band coaxial conical horn antenna.It can convert two coaxial TEM mode microwaves(1.717 GHz and 4.167 GHz)generated by the complex MILO into the coaxial TE11 mode microwaves,and then radiate them into the air.At 1.717 GHz,the gain of the antenna is 17.9 dB,and the total return loss and diffraction loss are 1.50%and 0,respectively.At 4.167 GHz,the gain is 19.4 dB,and the total return loss and diffraction loss are 1.17%and 0.78%,respectively.The power handling capacity of the antenna is 5.1 GW at 1.717 GHz and 2.0 GW at 4.167 GHz.Comparing with the original structure,the length of the dual-band radiation system is reduced by 45.2%.

Experimental investigation of a compact relativistic magnetron with axial TE_(11) mode radiation

As one of the relativistic electron tubes having compact configuration and high efficient output, the relativistic magnetron with direct axial radiation is very attractive in pulsed power and high power microwave fields for industrial and military applications. In this paper, the experimental investigation of a relativistic magnetron with axial TE11 mode radiation is reported. Under a total length of - 0.3 m, volume of - 0.014 m3, working at an applied voltage of 508 kV and a magnetic field of - 0.31 T, the relativistic magnetron radiates a microwave of 540 MW with the TE11 mode at 2.35 GHz in the axial direction. The power conversion efficiency is 15.0%. After a lot of shots, the detected amplitudes of microwaves are nearly the same. The fluctuations of wave amplitudes are less than 0.3 dB.