Microwave Beam Research Articles

Analysis of the Current Loading of an Accelerating Field Beam From a Lue-200 Accelerator

The current loading of an accelerated electron beam in the accelerating fields of a LUE-200 linear accelerator of the IREN facility at the Joint Institute of Nuclear Research (Dubna) is discussed. The LUE-200 accelerator consists of two accelerating sections operating on a traveling wave at a frequency of 2856 MHz with the microwave power compression systems of the SLED type. The limits of the accelerated beam current values are determined for various pulse durations of the beam current and microwave power levels fed into the accelerating sections. The calculation results are compared with the measured data.

Microwave Beam Bifurcation in an Inhomogeneous Plasma: Modeling by Ray Methods

Modification of the beam tracing method for numerical simulations is proposed that allows one to use it in the zones of the microwave beam bifurcation, which is accompanied by the linear mode transformation. The theoretical basis for this modification is the switching over to the hybrid spatial-spectral representation of two beams, within which both the beam axes coincide and, therefore, the paraxial approximation is still valid. The initial parameters of the beam split off from the “parent” beam are determined, and the equations are derived connecting the beam amplitudes in the bifurcation zone with each other.

Comparison of Terahertz, Microwave, and Laser Power Beaming Under Clear and Adverse Weather Conditions

Wireless transmission of power from point to point has been developed in two predominate electromagnetic frequency ranges: near-infrared and microwave. In this paper, the prospect of wireless power beaming in the terahertz frequency range is explored with emphasis on the role of adverse weather. Link distance, power transmission, and safety performance of near-infrared, microwave, and terahertz power beaming are compared under clear and adverse weather conditions. While infrared power beaming provides the longest link distances of the three under clear weather conditions, terahertz power beaming can provide better performance under adverse weather conditions.

Beam loading effects and microwave instability in the booster ring of a high intensity heavy-ion accelerator facility

Transient beam loading effects and microwave instability are very important in ion synchrotrons. A simulation code longitudinal particle tracking code (LPTC) based on multiparticle tracking is developed to simulate the beam loading effects and the longitudinal beam instabilities in the booster ring (BRing) of the High Intensity heavy-ion Accelerator Facility (HIAF). A process of beam capture, acceleration, debunching, and the second capture is simulated with a reference ion beam of ${^{78}\mathrm{Kr}}^{19+}$. The simulation results show that the beam loading effects have major contribution to the beam behavior during the debunching stage and the second capture stage. A feed-forward system is suggested to compensate the beam loading effects, and the main parameters of the feed-forward system are given. The microwave instability of coasting ${^{78}\mathrm{Kr}}^{19+}$ beams is observed from the simulation results. The threshold of the microwave instability is also given. The development of self-bunching and methods to suppress the microwave instability in the BRing are discussed.

Experimental Investigation of the Streamer Zone of Long‐Spark Positive Leader Using High‐Speed Photography and Microwave Probing

AbstractThe streamer zone of positive leader during the breakthrough phase of long sparks was experimentally investigated with two methods. One of the methods is the analysis of streamer‐zone images obtained with a high‐speed framing camera with image enhancement. This method allowed us to estimate the spatial distribution of streamer density and low‐frequency conductivity in the streamer zone. The other method is the microwave probing, which we applied for the first time to long sparks. The attenuation of microwave beam in the streamer zone in our experiments is proportional to the total number of free electrons inside the microwave beam. Experimental data on the microwave attenuation combined with the streamer density found using the first method allowed us to estimate the total number of free electrons in one streamer. The following parameters were obtained. The streamer density in the center of the streamer zone is (0.6–1) · 105 m−3, and the total number of streamers in the streamer zone is 4 · 105–106. The average total number of free electrons in one streamer is about 3 · 1010. Low‐frequency conductivity on the axis of streamer zone was estimated to be typically 2 · 10−5 S/m, which is similar to that estimated for corona sheath in lightning. Both methods are based on the assumption of constancy of electric field and similarity of all streamers inside the streamer zone. The overall results of this study are generally consistent with this assumption.

Optical emission spectroscopy of non-equilibrium microwave plasma torch sustained by focused radiation of gyrotron at 24 GHz

The excitation and gas temperature of a non-equilibrium argon plasma torch sustained by a focused 24 GHz microwave beam in the external atmosphere of air was measured by optical emission spectroscopy. The excitation temperature of argon atoms was found about 5000 K, while the vibrational and rotational temperatures of ambient nitrogen molecules were respectively estimated at 3000 K and 2000 K. The effective mixing of the external gas atmosphere into the plasma torch is experimentally demonstrated. The vibrational and rotational temperatures of nitrogen molecules slightly increased with the distance from the nozzle exit. Experimental results demonstrate that microwave discharge at atmospheric pressure may be relevant for the decomposition of highly stable molecules, e.g. carbon dioxide, in non-equilibrium conditions.

Discharge Modes Observed in Plasmas Sustained in Focused Microwave Beams

Plasma discharges are sustained in the focus of a continuous, high-power microwave beam. The experimental design minimizes interactions between the chamber walls and both the microwave beam and the resulting discharges so as to approximate free-space conditions. Discharges were generated by a multikilowatt, 4.7-GHz CW microwave beam at pressures ranging from 100 to 200 mtorr. The CW source enabled the evolution of the plasma-beam system to be observed over time scales ranging from seconds to hours. A variety of discharge behaviors are observed depending on the conditions (power, pressure, and gas composition) within the chamber. The observed discharges can be classified into three discharge modes: unstable, stable, and quasi-stable. Here, we present observations and a preliminary analysis of the various discharge modes observed in the experiment.

Treatment of cancer by radiotherapy and nanoparticles coupled with Methotrexate drug

Introduction: Cancer patients will receive Radiation therapy (RT) as part of their treatment as monotherapy or as part of a combination treatment. RT uses high-energy radiation such as photons and strong ions. Nanoparticles (NPs) are used for magnetic hyperthermia which increases the efficacy of RT and generates heat to kill cancer cells by destroying their DNA. Materials and Methods: NPs were prepared through the co-precipitation method and characterized using TEM, SEM, and X-ray diffractometer. 56 male mice were housed under the same environmental conditions. The animals injected into the right flank with 0.25mL from 106cells/mL Ehrlich tumor suspension. When tumors reach between 5-10mm in diameter, mice will be randomly divided into eight groups as follow,1stgroup: used as negative control group injected with 25μL phosphate buffer saline without treatment,2ndgroup:injected with Fe3O4-NPs,3rdgroup: injected with Fe2O3-NPs,4thgroup: injected with Methotrexate drug (MXT),5thgroup: injected with MXT, Fe3O4 and Fe2O3-NPs,6thgroup: as 5thgroup with microwave hyperthermia,7thgroup:as 5thgroup then treated with high energy photons and 8thgroup: as 5thgroup and exposed to electron beam therapy. Tumor volume and weight were measured after 15days.Tumor apoptosis was studied using histopathology and the tumor's side effects on biological systems were investigated. Results: The results indicate that the magnetic hyperthermia application is suitable for cancer treatment with microwave and linear accelerator treatment coupled with drugs. A significant decrease in tumor size, tumor necrosis and fibrosis were observed. Conclusion: It was found that Fe3O4 and Fe2O3-NPs coupled with MXT and exposed to electron beam therapy and microwave irradiation is the best method for cancer treatment.

Collective Thomson Scattering Diagnostic for Wendelstein 7-X at 175 GHz

The Collective Thomson Scattering (CTS) diagnostic measures the scattering spectrum of incident radiation off collective fluctuations in plasmas. In Wendelstein 7-X (W7-X) the diagnostic uses a 140 GHz heating gyrotron as a source of the probing radiation. At this frequency, the CTS spectra are heavily affected by the electron cyclotron emission, and the microwave beam propagation is restricted at typical W7-X plasma parameters. The diagnostic was successfully commissioned in the last experimental campaign and demonstrated ion temperature measurements. However, the signal-to-noise ratio was too low for measuring other quantities such as the fast-ion velocity distribution function or the fuel ion ratio. Currently, the W7-X CTS diagnostic is undergoing an upgrade to a frequency of 175 GHz. This will increase the sensitivity of the diagnostic, since the noise due to electron cyclotron emission will be reduced, and it will relax the constraints on microwave beam propagation in W7-X. Here we present the salient features of the upgraded CTS system and discuss its prospects for both thermal-ion and fast-ion measurements.

Fullwave Doppler reflectometry simulations for density turbulence spectra in ASDEX Upgrade using GENE and IPF-FD3D

Doppler reflectometry is an important microwave diagnostic for turbulent fusion plasmas. A microwave beam is scattered off density fluctuations, with wavenumbers according to incident frequency and relative direction. This way, a density fluctuation spectrum is measured. However, the correspondence between fluctuation power and scattered microwave power is strongly nonlinear. Studying these processes numerically therefore requires fullwave simulations (IPF-FD3D), with density fluctuations supplied by a separate plasma turbulence code (GENE). Earlier such attempts suffered from the low number of data points in the ‘interesting’ part of the spectrum, where a power law had to be fitted to 4 or 5 points. This has been overcome with recent simulations, which now show a much better agreement with experimental data.

Low-power-threshold parametric decay instabilities of powerful microwave beams in toroidal fusion devices

We discuss the experimental conditions responsible for a drastic decrease in the power threshold of parametric decay instabilities under auxiliary electron cyclotron resonance heating (ECRH) in toroidal magnetic fusion devices when the upper hybrid (UH) resonance for the pump wave is absent. We show that for a finite-width pump in the presence of a nonmonotonic (hollow) density profile occurring due to plasma equilibrium in the magnetic islands or anomalous particle fluxes from the ECR layer, 3D localization of one or both daughter waves is possible. This localization leads to the full suppression of daughter wave energy losses from the decay layer and a substantial increase in the nonlinear pumping efficiency. This decreases the power threshold of nonlinear excitation, which can be easily overcome in current ECRH experiments utilizing 1 MW microwave beams. Different scenarios of extraordinary and ordinary wave decays are investigated. The secondary decays of primary daughter waves and pump wave depletion are considered as the most effective mechanisms leading to the transition of primary instability to the saturation regime. The proposed theoretical model was shown to be able to describe the anomalous phenomena discovered in ECRH experiments in different toroidal fusion devices all over the world.

Reflective Focusing Based on Few-Layer Gradient Metasurface Element Array

This study proposes a three-layer focusing gradient metasurface for wavefront processing. The structure works in the frequency range of 15 to 25 GHz, and has a central frequency of 19.6 GHz. The metasurface unit is organized in a square and has high-impedance elements that reflect the full range of phase shifts. When the microwave beam is incident on this metasurface, the high-impedance elements modulate the beam according to the gradient arrangement, to realize the focusing effect of the lens, and the efficiency reaches 82%. The simulation results are consistent with the theoretical results.

Synthesis of Nitrogen Oxides in a Subthreshold Microwave Discharge in Air and in Air Mixtures with Methane

A subthreshold discharge excited by a microwave beam in air at pressures close to atmospheric is studied as a plasmachemical method of nitrogen oxide (NOx) production. It is shown that at the energy expenditure level (2–4) kW h/m3, it is possible to produce a nitrogen oxide concentration in pure air that exceeds the concentration in the initial gas by several orders of magnitude. At the same time, it is shown that it is possible to stop nitrogen oxide production almost completely by adding an admixture of methane (CH4) to the irradiated air, which makes the so-called self-non-self-sustained (SNSS) discharge much more promising for cleaning the gaseous exhausts from urban landfills from harmful admixtures (hydrogen sulfide, mercaptans, etc.).

Attitude control of space solar power satellite with large range of relative motion among subsystems

The transmitting antenna needs to be oriented to the Earth, while the PV cell array of the SSPS-OMEGA system rotates in a large range inside the concentrator for the orientation to the Sun, so that there is a large range of unfixed relative movement among the subsystems. For the study of dynamic characteristics and attitude control problem of the space solar power satellite, the multi-body dynamics model of the system is built, and the gravity gradient torque equation applied on the PV cell array is derived in the process of relative motion. A simple attitude control system and the corresponding electric thrusters configuration scheme are designed. The simulation results show that the attitude of 2-GW SSPS-OMEGA in roll and yaw direction is well controlled. However, due to the large range rotation of the PV cell array, the attitude in the pitch direction is controlled to converge to the microwave beam pointing accuracy of mechanical adjustment in longer time with the residual gravity gradient torque. In the long period, the attitude deviation angle in the pitch direction would stabilize periodically within ±0.018 degree. This provides a reference for further study of beam-control of the transmitting antenna.

Evaluation of Microwave Diathermy Effect on Equine Flexor Tendons: A Preliminary Study

Artificially induced tendinitis animal models are crucial to guarantee the significance and applicability of the study output. Herein, we propose that increasing tendon temperature could be a good model that is capable to mimic the clinically introduced tendinitis cases. Microwave radiofrequency radiation is one of the techniques used clinically to increase the heat of tissue situated superficial in the body. The aim of this study is to investigate the thermal effect of the microwave beam on the flexor tendons at the metacarpal/metatarsal region of donkey’s cadaver. Twelve hindlimb and twelve forelimb were obtained from six cadaveric donkeys were exposed to different microwave setting 30W/30min, 30W/15min, 25W/30 min, 25W/15min, 20W/30min and 20W/15min. The temperatures were recorded after each microwave session using a sensitive thermometer. Our results revealed a highly significant effect on temperature output between different watt setting and time at all the anatomical sites. Using of 30W/30min setting resulted in significantly higher temperature which estimated by 53.5±0.6, 47.5±0.6 and 45.5±0.6 Co at the following areas skin/superficial digital flexor tendon (SDFT), SDFT/ deep digital flexor tendon (DDFT) and DDFT/ Check ligament (CKL) respectively. Furthermore, we have demonstrated that increasing the exposure time is more effective in increasing the local temperature than increasing power exposure. In conclusion, the microwave diathermy can provide temperature gradient on flexor tendons that mimic that occurring during over exercise.

Локальные измерения флуктуаций радиальной скорости плазмы в токамаке ФТ-2 с помощью экваториального усиленного рассеяния

The possibility of local measurements of the level of the radial plasma velocity fluctuations by the equatorial enhanced scattering of a narrow microwave beam in the upper hybrid resonance in the core plasma of a tokamak is demonstrated. The limitations of the proposed method are clarified at the periphery of the plasma, where the amplitude of density fluctuations grows and small-angle scattering of microwaves on them along the path to the upper hybrid resonance and back becomes significant.

Second Harmonic 527-GHz Gyrotron for DNP-NMR: Design and Experimental Results.

We report the design and experimental demonstration of a frequency tunable terahertz gyrotron at 527 GHz built for an 800 MHz Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance (DNP-NMR) spectrometer. The gyrotron is designed at the second harmonic (ω = 2ω c) of the electron cyclotron frequency. It produces up to 9.3 W continuous microwave (CW) power at 527.2 GHz frequency using a diode type electron gun operating at V = 16.65 kV, Ib = 110 mA in a TE11,2,1 mode, corresponding to an efficiency of ~0.5%. The gyrotron is tunable within ~ 0.4 GHz by combining voltage and magnetic field tuning. The gyrotron has an internal mode converter that produces a Gaussian-like beam that couples to the HE11 mode of an internal 12 mm i.d. corrugated waveguide periscope assembly leading up to the output window. An external corrugated waveguide transmission line system is built including a corrugated taper from 12 mm to 16 mm i.d. waveguide followed by 3 m of the 16 mm i.d. waveguide The microwave beam profile is measured using a pyroelectric camera showing ~ 84% HE11 mode content.

Far-Infrared Investigation of the Benzene-Water Complex: The Identification of Large-Amplitude Motion and Tunneling Pathways.

The far-infrared spectrum of the weakly OH···π hydrogen-bonded benzene-water complex has been studied in neon and argon matrices, below 30 K. The in-plane water libration has been observed in both neon and argon for H2O and D2O complexed with C6H6 and C6D6 but not for the corresponding complexes involving HDO. Both H2O and D2O can tunnel between the two possible hydrogen bonds. This is not possible for HDO. The reported far-infrared observations have implications for the interpretation of the previously obtained molecular beam microwave spectrum of the benzene-water complex.

The Interaction of a High-Power Sub-Nanosecond Microwave Pulse With Plasma

We present the results of experiments, analytical modeling, and numerical particle-in-cell (PIC) simulations for the propagation of a high-power, sub-nanosecond microwave pulse through a plasma-filled cylindrical waveguide in a parameter regime not studied before. Depending on the experimental conditions, the non-linear interaction of the high-power microwave (HPM) pulse with the plasma results in self-channeling through it or causes the formation of a wakefield. To study this phenomenon, two backward wave oscillators (BWOs), operating in the super-radiant mode at frequencies of 9.6 and 28.6 GHz, were designed and tested. These BWOs were driven by an electron beam (~280 keV, ~1.5 kA, ~5 ns) generated in a magnetically insulated foil-less diode, from which it propagates through a slow wave structure guided by an external axial magnetic field. Microwave pulses of ~0.4-ns width, up to ~500-MW peak power at 9.6 GHz, and up to ~1.2 GW at 28.6 GHz were obtained. These powerful subnanosecond timescale microwave beam pulses were injected into the neutral gas, plasma, or their mixture in various configurations.

Metasurface-based ultra-lightweight high-gain off-axis flat parabolic reflectarray for microwave beam collimation/focusing

Ultra-lightweight deployable antennas with high-gain are pivotal communication components for small satellites, which are intrinsically constrained in size, weight, and power. In this work, we design and demonstrate metasurface-based ultra-lightweight flat off-axis reflectarrays for microwave beam collimation and focusing, similar to a parabolic dish-antenna. Our ultra-thin reflectarrays employ resonators of variable sizes to cover the full 2π phase range, and are arranged on the metasurface to realize a two-dimensional parabolic focusing phase distribution. We demonstrate a 30° off-axis focusing reflector that exhibits a measured gain of 27.5 dB at the central operating frequency of 11.8 GHz and a 3 dB directionality <pm 1.6°. Furthermore, we carry out full-wave simulations of the reflectarray, showing high gain of the beam focusing/collimation functionality, in good agreement with measurements. The demonstrated reflectarrays will enable low-cost, lightweight, and high-gain deployable transceivers for small-satellite platforms.