Determination of the cyclotron generation suppression band width in a plasma relativistic microwave generator

In a plasma-beam system in a finite magnetic field, along with Cherenkov resonance other resonances of beam and plasma waves occur. In a finite-length plasma waveguide, the concurrent wave excited by a beam at Cherenkov resonance is always partially reflected from the ends of the plasma waveguide. The reflected (counterrunning) wave provides feedback and leads to the occurrence of generation regime in such a system. Under the resonance condition for a normal Doppler effect the feedback is suppressed and the generation may cease. This effect can be used in experiments on creation of plasma microwave amplifiers in which microwave generation is harmful.     

Photonic generation of amplitude-and phase-modulated microwave signals with frequency and modulation bit-rate tunability

A photonic approach for the generation of an amplitude- and phase-modulated microwave signal with tun-able frequency and modulation bit-rate is proposed and demonstrated. Two coherent optical wavelengths are generated based on external modulation by biasing a Mach-Zehnder modulator (MZM) at the minimum transmission point to generate ±1-order optical sidebands while suppressing the optical carrier. The two sidebands are sent to a circulator and are then spectrally separated by a fiber Bragg grating notch filter. With one sideband being amplitude-modulated at another MZM and the other being phase-modulated at a phase modulator, a frequency-tunable amplitude-and phase-modulated microwave signal is generated by beating the two sidebands at a photodetector. The proposed technique is investigated theoretically and experimentally. As a result, a 20-GHz amplitude-modulated, 20-GHz phase-modulated, and 25-GHz amplitude-and phase-modulated microwave signals with tunable modulation bit-rate are experimentally generated.     

Generalized superposition of two squeezed states: generation and statistical properties

Superpositions of squeezed states were introduced by Sanders [Phys. Rev. A 39 (1998) 4284], Schleich et al. [Phys. Rev. A 38 (1988) 1177], Xin et al. [Phys. Rev. A 50 (1994) 2865], to investigate the occurrence of nonclassical properties of the quantized radiation field. In this report we present a generalized superposition state which interpolates between two arbitrary squeezed states. Nonclassical properties of this intermediate state as function of the interpolating parameters are studied, the previous results in the literature becoming a particularization of ours. An experimental proposal to generate this state is also presented.     

Radiation coupling with two‐dimensional electron systems in the low limit of the microwave band: magnetoresistance response

We report on a theoretical study of radiation‐induced resistance oscillations and zero‐resistance states in two‐dimensional electron systems when the irradiation frequency is very low. In this situation the photon energy is much smaller than the spacing between the Landau levels and therefore interlevel transitions are excluded. Experiments show that when these frequencies are used, resistance oscillations disappear and, instead, a strong suppression of magnetoresistance response is obtained. We apply the radiation‐driven electron orbit model concluding that the resistance suppression is a manifestation of an oscillation of very large wavelength. Under this regime we study the connection with larger frequencies and the dependence on radiation power and temperature. For high enough radiation intensity, we predict that a regime of zero‐resistance states can be reached at these low frequencies, too. The calculated results are in good agreement with experiments. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An electron in the field of phonons and magnons

The behaviour of a conduction electron in the presence of two Bose fields, namely, phonons and magnons in ferromagnetic semiconductors is studied. The effects of both electron-magnon and electron-phonon interactions on the energy renormalization are calculated.     

On the spectral and statistical properties of Rayleigh-Taylor mixing

Dynamics of turbulent mixing due to the Rayleigh-Taylor instability is considered. The mixing layer consists of a single horizontal array of large-scale structures. The characteristics of these structures are studied by the spectral and statistical methods. Mixing stimulation by long-wavelength noise is studied. It is demonstrated that, for typical homogeneous unscaled noise, self-similarity h∝t ² is retained. The threshold amplitude of random broadband noise is determined, below which this noise can be ignored. The mixing deceleration by the side boundaries is studied. The stimulation and deceleration effects sizably influence the mixing coefficient α₊, increasing and decreasing it, respectively.     

Power of microwave generation in an ultrarelativistic electron beam in the regime of virtual cathode formation in an externally applied magnetic field

A numerical study of the output power characteristics of microwave radiation from a relativistic electron beam (REB) with a virtual cathode in the presence of externally applied longitudinal magnetic field is performed. Typical dependences of the output microwave power of the relativistic vircator system on the external magnetic field strength are obtained, showing a number of local maxima. It is found that the characteristic behavior of the radiation power is determined by the conditions and mechanisms of virtual cathode formation in the presence of external longitudinal magnetic field and a self-magnetic REB field.     

Magnetic tunnel structures: Transport properties controlled by bias,magnetic field,and microwave and optical radiation

Different phenomena that give rise to a spin-polarized current in some systems with magnetic tunnel junctions are considered. In a manganite-based magnetic tunnel structure in CIP geometry, the effect of current-channel switching was observed, which causes bias-driven magnetoresistance, rf rectification, and the photoelectric effect. The second system under study, ferromagnetic/insulator/semiconductor, exhibits the features of the transport properties in CIP geometry that are also related to the current-channel switching effect. The described properties can be controlled by a bias, a magnetic field, and optical radiation. At last, the third system under consideration is a cooperative assembly of magnetic tunnel junctions. This system exhibits tunnel magnetoresistance and the magnetic-field-driven microwave detection effect.     

Dielectric properties of pyridine N-oxide aqueous solution under the static electric field and microwave field

Molecular dynamics simulations of the pyridine N-oxide aqueous solution have been performed in the canonical ensemble macroscopic canonical ensemble (NVT) both in the absence and presence of an external electromagnetic field. It extracts the radial distribution function for each concentration solution, dielectric constant and other information on dielectric properties. Analysing the microscopic dielectric information of the aqueous solution under the static electric field (0–3×10⁹ V/m) and microwave frequencies (2.45G, 0–3×10⁹ V/m), and comparing the dielectric information between the different concentrations and different field strengths, we can get the dielectric properties of two kinds of polar aqueous solution under microwave irradiation. Thus, this project can provide the data of the sample to other correlation studies.     

On the mechanism of occurrence of chaotic dynamics in a vacuum microwave generator with a virtual cathode

The nonlinear dynamics of an electron beam with a virtual cathode in a transit-current vircator system is numerically studied. The existence of complex modes, including chaotic ones, is shown. The physical processes in the electron beam are examined. It is found that the chaotic dynamics in an electron beam with a virtual cathode is due to the nonlinear interaction between the structures organized in it. “College,” State Education and Scientific Center of the State University, Saratov, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 9, pp. 1137–1146, September, 1998.     

Single-atom coherent field electron emitters for practical application to electron microscopy: Buildup controllability, self-repairing function and demountable characteristic

We have fabricated single-atom field emission (FE) tips by annealing Rh-deposited W tips at 900 K, and the FE characteristics were investigated. Due to the formation of the nanotips, the electron beams were confined in a semi-cone angle of 3°, an indication quite different from the conventional FE beams. In repairing-function test where the FE nanotips were intentionally destroyed beforehand, they recovered the peculiar FE characteristics by means of feasible low temperature annealing. Finally, we found that the present nanotips equipped the capability of recovering the unique FE properties even after an exposure to the air. These characteristics are significantly relevant to the practical applications to electron-optics instruments.     

用全带Monte Carlo方法模拟纤锌矿相GaN和ZnO材料的电子输运特性

报告了用全带MonteCarlo方法模拟纤锌矿相GaN和ZnO材料电子输运特性的结果.模拟所用的能带结构数据是用经验赝势法算得的.通过模拟得到了两种材料的平均漂移速度和平均能量与电场强度关系曲线,求得了电子迁移率.并且将两种材料的结果以及文献报道的GaAs的模拟结果进行了比较 关键词： 蒙特卡罗模拟 GaN ZnO 输运特性 能带结构     

On some singularities in the dielectric properties of an electron gas in a uniform magnetic field

The effects of a magnetic field on the self-shielding of an electron gas against small electrostatic perturbations V are studied by use of Bloch wave functions and by the random phase approximation. V is taken to be periodic along the field lines. It is demonstrated that in the weak field limit, $\text{μ}{}_0\text{B}\text{eV}\text{→ 0}$, magnetic effects become negligible. For μ₀B ? eV such effects may be important only under limited physical conditions. Singularities discussed by Glasser and Kaplan [1] are replaced by peaks of finite amplitude and width, appearing with the frequency of neck orbit oscillations. Peak profiles and the Lindhard singularity are investigated for the case V ≠ 0.     

Phenomenon of generalized synchronization in klystron chaos generators with delayed feedback: Experiment and numerical simulation

The system of unidirectionally coupled klystron chaos generators with delayed feedback has been experimentally and theoretically investigated. A new technique for diagnostics of generalized chaotic synchronization is proposed, which is based on the spectral analysis of a signal from a response klystron generator. Comparison of the obtained experimental and theoretical results is performed.     

On the transition radiation and bremsstrahlung from a relativistic electron with a nonequilibrium field

The problem of the transition radiation from an electron with a nonequilibrium self-field appearing in view of the sharp scattering of the electron has been considered. It has been shown that the state of the electron with the nonequilibrium field is manifested in the suppression of transition radiation and in the oscillatory dependence of its characteristics on the distance from a plate on which radiation occurs to the scattering point. The problem of the measurement of the characteristics of bremsstrahlung under the conditions when macroscopic transverse distances are responsible for the scattering process has been considered. It has been shown that the results of the measurement in this case significantly depend on the size of the detector and on its position with respect to the scattering point.     

On the invariance properties of the Klein-Gordon equation with external electromagnetic field

Abstarct Here we attempt to find the nature of the external electromagnetic field such that the KG equation with external electromagnetic field is invariant. Lie’s extended group method is applied to obtain the class of external electromagnetic field which admits the invariance of the KG equation. Though, the field potential only explicitly appears in the equation, the constraints for the invariance are only on the electromagnetic field. since deceased.     

On the mechanism of hydrogen atom and electron addition to phosphorus: An electron spin resonance study

A partir des spectres d'absorption du méthane naturel (1,1 pour cent de ¹³CH₄) enregistrés sur un spectromètre à grilles avec un parcours de 10 m, une pression de 10 torr et une résolution de 0,060 cm^-1, nous avons pu mesurer, avec une précision de pointé allant jusqu'à 0,004 cm^-1, 130 raies rotationnelles (correspondant à 150 transitions) de la bande ν₄ de la variété isotopique ¹³CH₄. Ces données ont permis de déterminer pour la première fois un jeu de treize constantes contribuant de façon significative à l'énergie jusqu'au quatrième ordre dans l'état vibrationnel v ₄=1. Pour les 150 transitions introduites dans le calcul, l'écart quadratique moyen est 0,020 cm^-1 et le plus grand écart n'excède pas 0,057 cm^-1. Les nombres d'ondes calculés sont donnés pour 233 transitions de la bande ν₄ de ¹³CH₄ allant de P 12 à R 13.