High-power Microwave Radiation Research Articles

Interaction of microwave radiation with an erosion plasma jet

The interaction of high-power pulsed microwave radiation with a plasma jet formed by a discharge in an ablative capillary is studied. A significant influence of microwave radiation on the plasma jet flow is found. Depending on the intensity of the initial perturbation of the jet, different scenarios of its evolution downstream are possible: attenuation or amplification accompanied with the development of turbulence up to the disruption of the flow if a certain threshold of the energy action is exceeded. A significant influence of the plasma jet and its state on the spatial position of the microwave energy release zone is found.

Ultra-low temperature MAS-DNP

Since the infancy of NMR spectroscopy, sensitivity and resolution have been the limiting factors of the technique. Regular essential developments on this front have led to the widely applicable, versatile, and powerful spectroscopy that we know today. However, the Holy Grail of ultimate sensitivity and resolution is not yet reached, and technical improvements are still ongoing. Hence, high-field dynamic nuclear polarization (DNP) making use of high-frequency, high-power microwave irradiation of electron spins has become very promising in combination with magic angle sample spinning (MAS) solid-state NMR experiments. This is because it leads to a transfer of the much larger polarization of these electron spins under suitable irradiation to surrounding nuclei, greatly increasing NMR sensitivity. Currently, this boom in MAS-DNP is mainly performed at minimum sample temperatures of about 100K, using cold nitrogen gas to pneumatically spin and cool the sample. This Perspective deals with the desire to improve further the sensitivity and resolution by providing “ultra”-low temperatures for MAS-DNP, using cryogenic helium gas. Different designs on how this technological challenge has been overcome are described. It is shown that stable and fast spinning can be attained for sample temperatures down to 30K using a large cryostat developed in our laboratory. Using this cryostat to cool a closed-loop of helium gas brings the additional advantage of sample spinning frequencies that can greatly surpass those achievable with nitrogen gas, due to the differing fluidic properties of these two gases. It is shown that using ultra-low temperatures for MAS-DNP results in substantial experimental sensitivity enhancements and according time-savings. Access to this temperature range is demonstrated to be both viable and highly pertinent.

Minimizing the impact of ground reflection on high power microwave E-field measurement

This paper presents a new measuring method of minimizing the impact of ground reflection on the microwave electronic field measurement using double antenna array. The character of ground reflection is studied using the electromagnetic geometric optics theory and the electromagnetic wave propagation formula in layered media. Then a theoretical formula for computing the oscillating period of ground scattering pattern is derived. The impact of ground reflection on the transversal field and vertical field is simulated using the FDTD method, and the effect of minimizing the ground reflection with double antenna array is also validated by simulation, it shows that the impact of ground reflection is decreased from 4 dB to less than 0.6 dB, which improves the accuracy of the high power microwave radiation field measurement.

Brain Glycogen Decreases During Intense Exercise Without Hypoglycemia: The Possible Involvement of Serotonin.

Brain glycogen stored in astrocytes, a source of lactate as a neuronal energy source, decreases during prolonged exercise with hypoglycemia. However, brain glycogen dynamics during exercise without hypoglycemia remain unknown. Since intense exercise increases brain noradrenaline and serotonin as known inducers for brain glycogenolysis, we hypothesized that brain glycogen decreases with intense exercise not accompanied by hypoglycemia. To test this hypothesis, we employed a well-established acute intense exercise model of swimming in rats. Rats swam for fourteen 20s bouts with a weight equal to 8% of their body mass and were sacrificed using high-power (10kW) microwave irradiation to inactivate brain enzymes for accurate detection of brain glycogen and monoamines. Intense exercise did not alter blood glucose, but did increase blood lactate levels. Immediately after exercise, brain glycogen decreased and brain lactate increased in the hippocampus, cerebellum, cortex, and brainstem. Simultaneously, serotonin turnover in the hippocampus and brainstem mutually increased and were associated with decreased brain glycogen. Intense swimming exercise that does not induce hypoglycemia decreases brain glycogen associated with increased brain lactate, implying an importance of glycogen in brain energetics during intense exercise even without hypoglycemia. Activated serotonergic regulation is a possible underlying mechanism for intense exercise-induced glycogenolysis at least in the hippocampus and brainstem.

Self-induced gaseous plasma as high power microwave opening switch medium

Self-induced gaseous plasma is evaluated as active opening switch medium for pulsed high power microwave radiation. The self-induced plasma switch is investigated for N2 and Ar environments under pressure conditions ranging from 25 to 700 Torr. A multi-pass TE111 resonator is used to significantly reduce the delay time inherently associated with plasma generation. The plasma forms under the pulsed excitation of a 4 MW magnetron inside the central dielectric tube of the resonator, which isolates the inner atmospheric gas from the outer vacuum environment. The path from the power source to the load is designed such that the pulse passes through the plasma twice with a 35 ns delay between these two passes. In the first pass, initial plasma density is generated, while the second affects the transition to a highly reflective state with as much as 30 dB attenuation. Experimental data revealed that virtually zero delay time may be achieved for N2 at 25 Torr. A two-dimensional fluid model was developed to study the plasma formation times for comparison with experimental data. The delay time predicted from this model agrees well with the experimental values in the lower pressure regime (error < 25%), however, due to filamentary plasma formation at higher pressures, simulated delay times may be underestimated by as much as 50%.

Electro-thermal coupled modeling of PIN diode limiter used in high-power microwave effects simulation

A major failure mode of positive-intrinsic-negative (PIN) diode limiter is the diode junction thermal burnout due to the high-power microwave (HPM) irradiation. Based on the time domain circuit approach, an electro-thermal coupled model including junction transient self-heating effects is presented via analogous between thermal dynamic and electronic circuit topology. Moreover, the proposed model takes into account feedback updating of physical parameters as device junction temperature varying. The diode junction thermal behavior is simulated and verified by the device manufacture measurements. The PIN limiter circuit numerical results of the microwave pulse width dependence on power level under HPM interference validate the well-known semi-empirical Wunsch–Bell relationship. And the turning point value of microwave pulse width obtained in simulations is very close to that specified in Wunsch–Bell formula.

Study of High-Power Ka-Band Rectangular Double-Grating Sheet Beam BWO

It is attractive to use sheet beam vacuum devices to generate high frequency, high-power microwave radiation. In this paper, we present the numerical and experimental studies of a high-power Ka-band sheet electron beam backward wave oscillator (BWO), in which the double-grating rectangular waveguide is used as the slow wave structure (SWS) for its thermal and mechanical robustness. The fundamental mode of this kind of SWS is an antisymmetric mode which has an antisymmetric longitudinal field distribution and will nonsynchronously interact with the electron beam on two sides of the electron channel along the vertical direction. We put forward a method to overcome this trouble in this paper. To drive this BWO, a high-power sheet beam is used with a cross section of 30 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\times\,$ </tex-math></inline-formula> 1 mm. A thin graphite cathode is used for its superiority in producing a high current, high-quality electron beam. For an experimental electron beam of 141 kV and 1668 A, the output power of over 46.8 MW at 31.68 GHz is obtained, which corresponds to a beam–wave interaction efficiency of 19.9%. Compared with the conventional hollow beam BWO and the single-grating rectangular waveguide sheet beam BWO, the double-grating sheet beam BWOs efficiency is higher, which indicates that the double-grating sheet beam device is promising for producing millimeter wave radiation with high power and high efficiency.

Neuronal‐activity‐dependent hippocampal glycolysis mediated by dopamine (1127.3)

Brain glycolysis (GLY) in the hippocampus (Hipp) plays a critical role in maintaining cognitive functions through energy supply and neuromodulation, mainly via noradrenergic (NA) and serotonergic (5-HT) regulation. However, it is still uncertain whether the occurrence of Hipp GLY depends on neuronal activity. Since running exercise elicits speed-dependent neuronal activation corresponding with energy demand, particularly in the Hipp, we elucidated this issue using a treadmill running model for rats. Rats ran on a treadmill at different speeds (slow: 10 m/min, moderate: 20 m/min, and high: 30 m/min), and were sacrificed using high-power microwave irradiation to detect glycogen, lactate, and monoamine levels in the brain (Hipp, cortex, cerebellum, brainstem etc.) after 30 min of running. Glycogen in the brain, except the hypothalamus, decreased in a speed-dependent manner, which was associated with speed-dependent increased and brain lactate levels. In the Hipp, decreased glycogen and increased lactate were associated with running-speed-dependent activated dopamine (DA), but not NA and 5-HT (Fig. 1A-E). Furthermore, antagonism of DA D2 receptors (not D1) prevented Hipp glycogen decrease during slow running (Fig. 1F). Here we provide the first evidence for neuronal-activity-dependent GLY mediated by DA D2 receptors in the Hipp, suggesting a possible role of DA in exercise-enhanced cognitive functions. $graphic_526FA3B5-3587-4B59-A802-1407F58DE9CB$ Grant Funding Source: This work was supported by JSPS

Effect of high power microwave radiation on liver injury and serum cytokine in rats

Objective To investigate the effect of high power microwave(HPM)radiation on morphology of liver cells and serum cytokines in rats.Methods Adult male Wistar rats were exposed to 100mW/cm2 intensity microwave radiation as experimental group,and rats without radiation were designed as normal controls.The blood samples were obtained from the hearts to determine the levels of aspartate transaminase(AST),alanine aminotransferase(ALT),interleukin(IL)-6,IL-10and IL-18on 1d,7dand 14dafter HPM radiation.Finally the rats were sacrificed and the right leaf tissues of liver were obtained immediately under ice bath,and the hepatic tissue changes were observed under routine light microscope.Results There were inflammatory cell infiltration,scattered,and patched cell degradation,and necrosis in rat hepatic lobule on1dand 7dafter HPM radiation;the situation was improved on 14dafter radiation,but there were still cell degradation and dotted necrosis.Serum levels of AST and ALT in the experimental group were significantly higher than those in the control group on 1dand 7dafter HPM radiation(P0.05,P0.01),but not on 14dafter radiation(P0.05).Serum levels of cytokines IL-6and IL-18in the experimental group were significantly higher than those in the control group on 1dand 7d after HPM radiation(P0.01),and the changes recovered somewhat on 14dafter radiation.Level of IL-10was decreasedafter radiation compared with the control group,with significant difference found on 1 dafter radiation(P 0.05).Conclusion HPM radiation can cause damage to liver structure and function,which might be associated with the changes of serum IL-6,IL-10and IL-18levels.

Characterization of High Power Microwave Radiation by an Axially Extracted Vircator

Characterization results of high-power microwave radiation, from an axial vircator driven by pulsed electron beam accelerator AMBICA-600 are reported in this paper. We present a study on variation in pulsed microwave power output and dominant frequency by discretely varying anode-cathode (A-C) gap. While keeping the cathode diameter fixed at 40 mm, for the A-C gap distance in the range 5-9 mm, dominant frequencies have been measured to be lying in the range 4.7-9.8 GHz. The trend of a subsequent increase in the dominant frequency at lower A-C gap distances (and vice versa) revealed that center frequency is mainly governed by the longitudinal size of the potential well. The highest microwave power of ~ 14 MW for ~ 75-ns pulse duration was obtained at A-C gap of 7 mm having the dominant frequency in C-band at ~ 6.9 GHz. The beam-to-microwave power conversion efficiency of ~ 1.2% has been demonstrated in our experiments. On the basis of power distribution pattern obtained by the gas breakdown technique, the dominant mode of emission is believed to be transverse magnetic mode. Relative analysis of frequency spectrums obtained for various A-C gap distances evidenced experimental recognition of optimum A-C spacing as a generation of narrowband distinct frequency peak of large magnitude with minimal mode hopping.

Design and experiment of a cross-shaped mode converter for high-power microwave applications

A compact mode converter, which is capable of converting a TM01 mode into a circularly polarized TE11 mode, was developed and experimentally studied with high-power microwaves. The converter, consisting of two turnstile junctions, is very short along the wave propagation direction, and therefore is suitable for designing compact and axially aligned high-power microwave radiation systems. In this paper, the principle of a converter working at 1.75 GHz is demonstrated, as well as the experimental results. The experimental and simulation results are in good agreement. At the center frequency, the conversion efficiency is more than 95%, the measured axial ratio is about 0.4 dB, and the power-handing capacity is excess of 1.9 GW.

Low-Voltage Cyclotron Resonance Maser

The gyrotron, which is the most powerful cyclotron resonance maser (CRM), is an extremely effective device to generate high-power microwave radiation. It is used in microwave heating of thermonuclear plasma, radar, and other industrial applications. However, the gyrotron has one basic problem. It requires relativistic (very high energy) electrons. These require very high voltages to produce, and, in turn, relativistic electrons produce intense and dangerous X-rays in the collector region. In this paper, we discuss an alternate method of operation that does not require high voltages. We have also constructed a low-voltage CRM that operates at 2.2 kV and produces 8 GHz at a magnetic field of 0.3 T. In principle, the device should operate at even lower voltages.

The effect of strong microwave electric field radiation on: (1) vegetable seed germination and seedling growth rate

The effect of high power microwave (HPM) irradiation on seed germination and seedlings was evaluated. Vegetable seeds were subjected to HPM irradiation. The main focus was on the thermal heating elimination during seeds irradiation. For that reason short high frequency microwave pulses were used. The study object was seeds of different harvest years (2000, 2003 and 2008) of radish (Raphanus sativus L.) variety ‘Babtų žara’, tomato (Lycopersicon esculentum Mill.) variety ‘Viltis’, carrot (Daucus sativus Rohl.) variety ‘Vaiguva’ and tomato (Lycopersicon esculentum Mill.) variety ‘Red Cherry’ (seeds harvested in 1980). In the first experiment, all seeds were exposed to microwaves at 9.3 GHz frequency for 10 min. In the second experiment, carrots ‘Vaiguva’ seeds (11 years-old) were exposed to microwaves at 9.3 GHz frequency for 5 and 20 min and exposed to 2.6 and 5.7 GHz microwaves for 10 min. To establish microwave effect on seedling growth rate, tomato, carrot and radish seeds harvested in 2008 were exposed to microwaves at 9.3 GHz frequency for 10 min. It was established that 11 year-old radish seeds exposed to 9.3 GHz microwaves had higher germination as compared with non-irradiated seeds. HPM increased radish germination energy by 6% in seeds harvested in 2003. HPM exposure significantly increased the germination energy and germination of 8 year-old carrot seeds. The highest carrot seed germination was established at 9.3 GHz microwave frequency under 5 min exposure. Seed exposure to HPM (9.3 GHz) had a significant positive effect on dry weight of tomato seedling shoots and on tomato and radish seedling height, but it had negative influence on carrot seedling height. Seed irradiation with HPM (9.3 GHz) had a significant positive effect on the amount of chlorophyll a, chlorophyll b, chlorophylls a + b and carotenoids in tomato seedlings’ fresh mass, but the opposite effect was determined in carrot seedlings’ fresh mass.

Generation of multi-charged high current ion beams using the SMIS 37 gas-dynamic electron cyclotron resonance (ECR) ion source

A gas-dynamic ECR ion source (GaDIS) is distinguished by its ability to produce high current and high brightness beams of moderately charged ions. Contrary to a classical ECR ion source where the plasma confinement is determined by the slow electron scattering into an empty loss-cone, the higher density and lower electron temperature in a GaDIS plasma lead to an isotropic electron distribution with the confinement time determined by the prompt gas-dynamic flow losses. As a result, much higher ion fluxes are available; however a decrease in the confinement time of the GaDIS plasma lowers the ion charge state. The gas-dynamic ECR ion source concept has been successfully realized in the SMIS 37 experimental facility operated at the Institute of Applied Physics, Russia. The use of high-power (∼100kW) microwave (37.5GHz) radiation provides a dense plasma (∼1013cm−3) with a relatively low electron temperature (∼50–100eV) and allows for the generation of high current (∼1A/cm2) beams of multi-charged ions. In this work we report on the present status of the SMIS 37 ion source and discuss the advanced numerical modeling of ion beam extraction using the particle-in-cell code WARP.

Study of superradiance based on a low-voltage backward wave oscillator

According to the small size requirement for wide-band high-power microwave radiation, a superradiance backward wave oscillator (BWO) is proposed to generate such high-power microwave radiation with a low voltage (∼20 kV) pulse power supply and low guiding magnet field (∼0.1 T). In order to get a high-efficiency C-band superradiance BWO with a low beam voltage and a low guiding magnet field, the mechanism of superradiance in a BWO is explored in particle-in-cell simulation. With the oversized structure, the simulation shows that a microwave power of 405 kW with a frequency of 5.6 GHz and a spectrum width of 500 MHz can be obtained with a voltage of 23 kV and magnetic field of 0.1 T.

Effect of Low Power Microwave Radiation on Microorganisms and other Life Forms

Microwaves are a part of electromagnetic spectrum with multiple applications. Thermal effects resulting from high-power microwave radiation are well established, but considerable controversy surrounds the possible microwave specific athermal effects. Reports suggesting its presence or absence keep accumulating in literature. Exact mechanism through which low-power microwave radiation exerts its effect on different life forms including microorganisms yet remains to be elucidated. For this effective experimental strategies needs to be devised, where thermal and athermal effects can be studied separately. Identifying suitable biological model(s) for such studies is also required. This review focuses on the effects of low-power mi- crowave radiation on different life forms, particularly microorganisms. Effects of low-power microwave on growth and enzyme activity of microbes are described. Factors affecting the interaction of microwaves with living systems, such as microwave power, frequency, exposure duration, continuous vs. pulsed treatment, etc. has also been covered. The possibility of using mi- crowaves for mutagenesis (strain improvement) has also been indicated.

小型超宽谱高功率微波辐射系统

A compact ultra wide spectrum high power microwave radiation system made up of 100 kV nanosecond pulse generator, subnanosecond gas switch and TEM horn antenna is designed. The output voltage waveform of the pulse generator is a pulse with a rising time of 280 ps, a decaying time of 180 ps and a peak amplitude of 100 kV. The system can work at 100 Hz repetition rate and the peak radiating field on boresight is about 10 kV/m at the distance of 7.5 m. The -3 dB bandwidth of the radiated field is from 230 MHz to 810 MHz and -20 dB bandwidth is from 100 MHz to 1.3 GHz. The system with small volume of 80 cm50 cm26 cm and the weight of 45 kg is expected to find many applications in areas of high power microwave.

Study of Basic Effects of HPM Pulses in Digital CMOS Integrated Circuit Inputs

The potential of high-power microwave radiation to couple into and generate malfunction in microelectronic systems has become a serious concern; however, the underlying electronic mechanisms are not well understood. We present results of experiments on the response of a typical CMOS integrated circuit to pulsed microwave excitation. Our results show that electrostatic discharge protection devices detect the pulse envelope of the microwave carrier via its nonlinear conductance. The device characteristics are analyzed using device physics to describe the quasi-static and non-quasi-static behavior of the protection circuits and define the regime of operation in terms of excitation frequency. The results of experiments and analysis lead to the development of an improved effects model based on Berkeley Short-channel IGFET Model using a body resistor network. Good agreement between experiments and transient and harmonic-balance simulations is demonstrated. The results show that a deterministic method of evaluating electromagnetic effects using physical, scalable device parameters is feasible.

Simulation and solving the descriptive equations on the voltage breakdown in ultra-quick circuit breakers

This paper presents descriptive equations on the voltage breakdown in ultra-quick circuit breakers (UQCB). In this paper, main breakdown characteristics of UQCB\'s are presented. Gaseous breakdown in the sub-nanosecond regime is of interest for fast pulsed power switching, short pulse electromagnetics, and for plasma limiters to protect devices from high power microwave radiation. In order to study pulsed gas breakdown initiation dynamics, a sub-nanosecond voltage pulse is simulated by Electro-Magnetic Transient Program (EMTP). Keywords: Ultra Quick circuit breakers, Voltage breakdown, Gaseous breakdown, Transient recovery voltage.

Generation of high charge state metal ion beams by electron cyclotron resonance heating of vacuum arc plasma in cusp trap

A method for generating high charge state heavy metal ion beams based on high power microwave heating of vacuum arc plasma confined in a magnetic trap under electron cyclotron resonance conditions has been developed. A feature of the work described here is the use of a cusp magnetic field with inherent "minimum-B" structure as the confinement geometry, as opposed to a simple mirror device as we have reported on previously. The cusp configuration has been successfully used for microwave heating of gas discharge plasma and extraction from the plasma of highly charged, high current, gaseous ion beams. Now we use the trap for heavy metal ion beam generation. Two different approaches were used for injecting the vacuum arc metal plasma into the trap--axial injection from a miniature arc source located on-axis near the microwave window, and radial injection from sources mounted radially at the midplane of the trap. Here, we describe preliminary results of heating vacuum arc plasma in a cusp magnetic trap by pulsed (400 μs) high power (up to 100 kW) microwave radiation at 37.5 GHz for the generation of highly charged heavy metal ion beams.