Spectrum Of Microwave Radiation Research Articles

PIC Simulation of the High-Power Microwave Radiation in a Radial-Type Reflex Triode With a Converging Magnetized Electron Beam

A particle-in-cell simulation of a powerful reflex triode with a radially converging magnetized electron beam was carried out. The complex dynamics of the electron beam and the generation characteristics of the reflex triode were studied. It is shown that a virtual cathode and, for the first time, a disk-shaped squeezed state of the beam were formed in it. Radial profiles of the electron temperature and a number of electrons in the squeezed state were calculated. It was calculated that the peak microwave power reaches $P =300$ MW and the average power $ =115$ MW at a beam current of $I_{0} =5$ kA and cathode potential of $U_{c} = -100$ kV. The microwave radiation spectrum is noise-like in the range 0–15 GHz.

PIC-моделирование генерации CВЧ-излучения в отражательном триоде радиального типа с расходящимся замагниченным электронным пучком

This paper presents particle-in-cell simulation of the reflex triode with radially diverging magnetized electron beam. Dynamics of the electron beam and generation characteristics of the reflex triode are studied in the work. It is shown that two virtual cathodes are formed in it. It was calculated that the peak power of the microwave radiation reaches P=19 MW at the beam current I0=5 kA and potential of the cathode Uc=‒100 kV. There is a peak in the microwave radiation spectrum at the frequency ν = 5.2 GHz.

Effect of the Distance of Plasma–Beam Interaction on the Oscillation Regimes in a Plasma Relativistic Microwave Oscillator

We study the effect of the distance of plasma–beam interaction on the parameters of the output radiation of a plasma relativistic microwave generator (PRMO). In the experimental PRMO based on the Sinus 550-80 accelerator, the characteristics of the output microwave radiation (spectral width, spectral density of the amplitude of the radiation) vary during a single pulse of the relativistic electron beam (REB). We analyze and numerically simulate the experimental data; the geometric and physical parameters of the device used in the simulation are close to those in the experiments. We show that increase in the distance of the plasma–beam interaction (the length of the system) causes the duration of the effective microwave pulse generation to approach that of the REB despite the presence of ion background and the plasma density profile modification, i.e., no disruption or change in the generation regime occurs during the REB pulse, while the microwave radiation spectrum broadens.

Wideband antenna for detecting high-power microwave radiation pulses

The plasma relativistic generator (PRG) at the Sinus 550-80 accelerator has a number of unique properties, such as the single- and multiple-pulse (up to 50 pulses per second) generation modes, generation of microwave pulses with a duration of up to 80 ns and frequencies of 2 to 25GHz, and generation of monochromatic and wide-spectrum radiation. The carrier frequency and the spectrum width can be controlled by varying the experimental parameters, e.g., the plasma density. To investigate the PRG operation modes, appropriate devices for detection of the PRG microwave radiation are needed. In this work, numerical models of antennas with different geometrical parameters are developed using the Ansoft HFSS 13.0 CAD and an antenna with the optimum parameters is proposed for measuring microwave radiation spectra in the desired frequency range at a power level of 50 to 100MW.

Peculiarities of millimeter range autodynes

A functional diagram and an equivalent circuit diagram of an autodyne oscillator are presented in the paper. Features of the formation of autodyne and noise characteristics are discussed taking into account the nonlinearity of autodyne phase characteristics. Analytical expressions for the noise process are given for the case of simultaneous influence of the autodynes reflected self-radiation and self-noise on the autodyne. The positive influence of the use of an external high-Q resonator on the formation of low-frequency data signals is shown. It consists in the increase of the dynamic range, reduction of autodyne frequency deviation, narrowing of microwave radiation spectrum. The results of experimental research of conventional autodynes and those stabilized by an external high-Q resonator are presented in the paper.

Observations and modeling of the spatial distribution and microwave radiation spectrum of the active region NOAA 11734

Microwave observations of the solar active region NOAA 11734 were done on April 28–May 8, 2013 with SSRT and the RATAN-600 radio telescopes. As a result of observations, two-dimensional distributions of the Stokes parameters I and V were obtained according to data from the SSRT at a frequency of 5.7 GHz and a microwave radiation spectra in the range of 3–18 GHz according to data from the RATAN-600. It was found that sunspots of the active region have an anomalous polarization that corresponds to the O-mode of microwave emisson up to 16 GHz. In order to explain the radio emission characteristics, the structure of the magnetic field in the nonlinear force-free approximation is restored, and free-free and gyroresonance radio emission are simulated. Maps of the model distribution of the brightness temperatures of both circular polarizations of the radio emission that replicate the observed spatial structure of the polarization on all days of observations were constructed. Analysis of the observational data and radio emission modeling make it possible to explain the characteristics of the polarization distribution within the mechanism of the weak interaction of radio emission modes in the quasi-transverse magnetic field above sunspots (Zheleznyakov, 1997).

Identification of deuterium and tritium isotopes in water by microwave radioscopy

For the first time, the microwave radiation spectra were recorded for light water H2O, heavy water D2O, and D2O containing a small amount of T2O. The spectra were analyzed by a special program on a PC. The measurement results showed that not only can the proposed method distinguish between the substances by composition or concentration, but also it can determine the presence of heavy and superheavy hydrogen isotopes in normal water.

Calculation of magnetic fluid parameters from the temperature dependence of the microwave reflection spectrum

We analyze the possibility of determining three parameters of a magnetic fluid (permittivity, volume fraction of the solid phase, and diameter of magnetic fluid particles) simultaneously from the temperature dependence of the reflection spectrum of microwave radiation. The reflected signal is detected using a microwave interferometer in a magnetic field, and the microwave interferometer is loaded with a layer of a magnetic fluid. Analysis of the spectral dependence of the reflection coefficient and its temperature dependence makes it possible to get information on the properties of the magnetic fluid under investigation, to refine the value of the permittivity of the magnetic fluid, and to obtain the effective permittivity of nanosize magnetic particles.

Microwave radiation in the upper atmosphere of the earth during strong geomagnetic disturbances

The influence of N2 and O2 molecules on spontaneous microwave radiation spectrum was studied over the decimeter range. This radiation appears in the D and E upper earth atmosphere layers during strong magnetic storms. It was shown to be caused by radiation transitions between medium-perturbed orbitally degenerate Rydberg atom and molecule states A** that occur without changes in the principal quantum number, δn = 0. The available experimental data were used to calculate the dependences of orbitally degenerate state populations on the density of medium and electron flux and temperature. Effective radiation bands were constructed for transitions between highly excited quasi-molecule levels A**N2 and A**O2. The emission spectrum was shown to be inhomogeneous and contain three frequency regions in which a noticeable decrease in the intensity of radiation occurred. The physical reason for the formation of these regions was a shift of the emission spectra of quasi-molecules containing unexcited N2 and O2 molecules. The frequency profiles of radiation intensity within these frequency regions were calculated as depending on the storm level. Radiation profiles were shown to noticeably change as the storm level increased, they strongly increased close to the right region edge corresponding to high transition frequencies. Nonmonotonic behavior of this profile in the middle of the lower region was observed; this was related to emission spectrum inhomogeneity. A sharp increase in radiation intensity as the magnetic storm level increased occurred in the region of frequencies situated close to the right edge of the upper region (50–100 GHz), which was most interesting for biophysical studies of the action of microwave radiation on living organisms during strong geomagnetic disturbances.

Ion Noise in the Plasma-Assisted Slow-Wave Oscillator

The theory describing the effect of ion oscillations on the spectrum of outgoing microwave radiation in plasma-assisted slow-wave oscillators (pasotrons) is developed. It is shown that the most important are the variations of ion density in the potential well formed by electron beam in the space between the plasma gun and an aperture installed at the entrance to the interaction space. These fluctuations cause temporal variations in the Budker parameter that is responsible for the ion focusing of the beam. After the focal plane, the beam electrons radially diverge and are intercepted by the wall of a slow-wave structure. In the presence of oscillations in ion density, the beam interception also becomes time dependent, which affects the spectrum of microwave radiation. The results obtained allow one to interpret experimental data and can also be used for minimizing the ion sidebands in the spectrum of pasotron radiation.

Fractional ac Josephson effect in unconventional superconductors

For certain orientations of Josephson junctions between two px-wave or two d-wave superconductors, the subgap Andreev bound states produce a 4π-periodic relation between the Josephson current I and the phase difference φ: I∝sin(φ/2). Consequently, the ac Josephson current has the fractional frequency eV/ℏ, where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (and not the square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring the frequency spectrum of microwave radiation from the junction.

Fractional ac Josephson effect in p- and d-wave superconductors

For certain orientations of Josephson junctions between two p x -wave or two d-wave superconductors, the subgap Andreev bound states produce a $4\pi$ -periodic relation between the Josephson current I and the phase difference $\phi$ : $I\propto\sin(\phi/2)$ . Consequently, the ac Josephson current has the fractional frequency $eV/\hbar$ , where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring frequency spectrum of microwave radiation from the junction. We also study junctions between singlet s-wave and triplet p x -wave, as well as between chiral $p_x\pm ip_y$ -wave superconductors.

Cyclotron lines in the spectra of solar flares and solar active regions

It was shown by Zheleznyakov and Zlotnik (1980a, b) that in complex configurations of solar magnetic fields (in hot loops above the active centres, in neutral current sheets in the preflare phase, in hot X-ray kernels in the initial flare phase) a system of cyclotron lines in the spectrum of microwave radiation is likely to be formed. Such a line was obtained by Willson (1985) in the VLA observations at harmonics of the electron gyrofrequency. This communication interprets these observations on the basis of an active region model in which thermal cyclotron radiation is produced by hot plasma filling the magnetic tube in the corona above a group of spots. In this model the frequency of the recorded 1658 MHz line corresponds to the third harmonic of electron gyrofrequency, which yields the magnetic field (196 ± 4) G along the magnetic tube axis. The linewidth Δf/f ∼ 0.1 is determined by the 10% inhomogeneity of the magnetic field over the cross-section of the tube; the line profile indicates the kinetic temperature distribution of electrons over the tube cross-section with the maximum value 4 × 106 K. Analysis shows that study of cyclotron lines can serve as an efficient tool for diagnostics of magnetic fields and plasma in the solar active regions and flares.

Cyclotron Lines in the Spectra of Solar Flares and Solar Active Regions

AbstractIt was shown by Zheleznyakov and Zlotnik (1980a, b) that in complex configurations of solar magnetic fields (in hot loops above the active centres, in neutral current sheets in the preflare phase, in hot X-ray kernels in the initial flare phase) a system of cyclotron lines in the spectrum of microwave radiation is likely to be formed. Such a line was obtained by Willson (1985) in the VLA observations at harmonics of the electron gyrofrequency. This communication interprets these observations on the basis of an active region model in which thermal cyclotron radiation is produced by hot plasma filling the magnetic tube in the corona above a group of spots. In this model the frequency of the recorded 1658 MHz line corresponds to the third harmonic of electron gyrofrequency, which yields the magnetic field (196 + 4) G along the magnetic tube axis. The linewidth Af/f ∼ 0.1 is determined by the 10% inhomogeneity of the magnetic field over the cross-section of the tube; the line profile indicates the kinetic temperature distribution of electrons over the tube cross-section with the maximum value 4 x 106 K. Analysis shows that study of cyclotron lines can serve as an efficient tool for diagnostics of magnetic fields and plasma in the solar active regions and flares.

Microwave Radiation Peculiarities of Vegetative Covers

The theoretical and experimental microwave radiation spectra of vegetation-covered soil are presented. The experiments were performed both under laboratory conditions and from aircraft in the wavelength range from 0.8 to 30 cm.

Effect of coherent synchrotron oscillations on the spectrum of microwave radiation of electrons in storage ring

The paper studies the characteristics of the microwave radiation of relativistic electrons in a storage ring given coherent synchrotron oscillations of the particles in the beam. Within the frame work of the collective phase motion model constructed, it is shown that the band of the generated harmonics is broadened considerably and the power of the coherent losses exceeds the analogous characteristics of the radiation of a beam of particles moving independently.

Intense microwave generation by the negative-mass instability

This paper examines the negative-mass stability properties of an E layer for transverse electric (TE) and transverse magnetic (TM) waveguide modes in a conducting cylinder. The analysis is carried out for a relativistic non-neutral E layer aligned parallel to a uniform axial magnetic field B0êz, within the context of the assumptions that the electron motion is ultrarelativistic (γ0≫1) and that (ν/γ0)1/3≪1, where ν is Budker’s parameter and γ0mc2 is the electron energy. One of the most important features of the analysis is that the axial energy spread can have a large influence on the stability behavior for both the TE and TM waveguide modes. By an appropriate choice of system parameters, it is shown that the spectrum of microwave radiation generated by the negative-mass instability can be very narrowband.

The electromagnetic radiation near the ion plasma frequency emitted by a turbulently heated plasma

Abstract The microwave radiation spectrum from a turbulently heated plasma is measured in detail. Characteristic frequencies of the ion-acoustic instability and the electron-ion two-stream instability are observed.

OBSERVATION OF THE SPECTRUM OF MICROWAVE RADIATION SCATTERED FROM A NONEQUILIBRIUM LIQUID

Measurements of the spectrum of microwave radiation scattered from a nonequilibrium liquid (CCl4 at 71°C) are presented. It is shown that the mean drift velocities of the refractive index inhomogeneities responsible for the scattering can be measured. The experimental results are consistent with the theory of wave propagation in a turbulent medium.

The spectrum of microwave radiation from InSb

The frequency spectrum of the microwave radiation emitted from InSb in the presence of applied electric and magnetic fields at 77°K was observed using a spectrum analyzer. In the frequency region from 7 to 26 Gc/s the spectrum showed oscillatory behavior with a period of 2.2 Gc/s, with the average value decreasing with increasing frequency. Such a structure could be due to a series of harmonics of a fundamental mode with frequency of 2.2 Gc/s. The frequencies of the peaks did not shift on changing the magnetic field and current. The spectrum near the frequency of 2.2 Gc/s was measured in detail in a coaxial-type cavity. The intensity of the radiation in this frequency region was much higher than that in the higher frequency region. The spectrum did not show clearly the expected peak at 2.2 Gc/s, but showed a further oscillatory behavior with a period of about 150 Mc/s. The physical mechanism which gives such a structure to the spectrum is not yet understood. It was also observed that the threshold conditions for the observation of radiation depended on the sample geometry, the thresholds being lower for thin samples, with the magnetic field perpendicular to both the current and the thin direction.