Radiophysics and Quantum Electronics最新文献

The problem of establishing the relationship between the surface currents and the radiation field of a perfectly conducting half-plane excited by slots of various shapes (constant width, linearly or exponentially expanding, etc.) perpendicular to the edge of the half-plane is solved. The relationships are obtained which allow one to calculate the currents induced on the surface of a half-plane affecting the radiation-field creation. The relationship of the surface currents on the half-plane with radiation patterns (RP) of the corresponding slot antennas (SA) is established. The curves of the surface currents and RP for SA of constant width are calculated on the basis of the obtained formulas. The patterns of variation in the current dependences on the geometric dimensions of the slot and their effect on the corresponding RP were established. It has been shown that experimentally measured RP for similar experimental SA confirm the identified regularities for the corresponding design currents and RP, and make it possible to establish the applicability range for the obtained mathematical models. The SA studies were carried out in the frequency range 8–12 GHz (the average frequency is 10 GHz). The validity of the obtained models in this frequency range is shown.

We present a modification of the method for synthesizing the surface of waveguide transducers, which are developed at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), in combination with solving of a system of scalar integral equations for the surface electric current. Since the synthesis procedure operates on the components of the electromagnetic field on the surface, which are unambiguously related to the current, the specified equations are integrated into it seamlessly. The equations are derived from the original vector integral equation of iterative physical optics, which is a method for analysis of electromagnetic fields in oversized systems, for a waveguide with a smooth wall deformation. The method is used in the calculation of high-power microwave devices (gyrotrons) and for the synthesis of waveguide emitters that convert the high-frequency operating mode into a quasi-Gaussian field distribution at the output by using a smooth shallow deformation of the waveguide. The possibility of significantly accelerating the synthesis while maintaining the high efficiency of the obtained profile is shown using the example of an emitter operated at a frequency of 184 GHz with the TE_28.13 mode.

We consider effects leading to the generation of quasi-stationary fields and radiation of electro-magnetic waves during the propagation of an optically excited discharge pulse in extended targets. The results of numerical simulation are presented for the interaction of an ultrashort laser pulse of relativistic intensity with an extended dense target and for the transformation of this pulse into a powerful discharge current pulse. It is shown that, under certain conditions, such a pulse can be used to generate strong electromagnetic fields with specified spatiotemporal properties. Particular attention is paid to the influence of parameters of the discharge pulse on the properties of the induced electromagnetic fields. Analysis of the discharge-pulse profile as a function of the target thickness is provided and the dynamics of the evolution of the discharge-pulse profile on a time scale of about ∼ 10 ps, when the distance traveled by the pulse along an extended target is of the order of 3 mm, is studied.

We present the results of calculating and studying experimentally a gyrotron working at the third harmonic of the cyclotron frequency. It used an electron-optical system that generated an electron beam with a particle energy of 280 keV and a current of up to 50 A. Coupled cavities with mode transformation were used as a selective element. The pulsed output power of the gyrotron radiation reached 0.8 MW at a frequency of 80 GHz with an efficiency of about 14%. The generation power was limited by a microwave breakdown in the first section of the cavity.

The compact laboratory setup “Solar Wind” (IAP RAS) forms an arch-shaped structure of the coronal-loop type, in which the plasma pressure varies from zero to values of the order of or above the magnetic pressure. The arc discharge at each footpoint of the magnetic tube creates a plasma characterized by a significantly higher ion temperature along the magnetic field line than across it. In the stationary state (when the ion pressure remains below the threshold for rupture of the system at the loop apex), the plasma is found to be stratified either as a cylindrical layer along the outer wall of the tube or, possibly, as two belts along the upper and lower vaults of the arch. The paper discusses the excitation of a torsional Alfvén oscillation in the loop under firehose-instability conditions. In the case of rapid growth (with an increment on the order of the ion cyclotron frequency), the unstable Alfvén oscillation substantially redistributes particles between the central axis and the tube wall, manifesting itself as the observed cylindrical layer.

We present the results of modeling of propagation of HF radio waves on the Cyprus—Nizhny Novgorod path during recording of traveling ionospheric disturbances (TIDs) manifested on the distance–frequency characteristic as z-structures. The ray paths of waves propagating in a smoothly inhomogeneous magnetized ionospheric plasma were calculated for the conditions of experiments conducted in the summer of 2023. The model disturbance of the ionospheric electron density profile during the passage of a TID was specified as a periodic structure with a certain number of periods, which was simulated by a harmonic function exponentially limited in altitude. The model parameters were selected by the best match between the modeling results (calculated distance–frequency characteristics (DFCs)) and the experimentally recorded DFCs of oblique ionospheric sounding.

We study the possibility of using the mode of stimulated backscattering on a weakly relativistic electron beam with a variable energy to implement a frequency modulator in the subterahertz frequency range. It is shown that of the two mechanisms of saturation of the scattered-wave amplitude growth, which are pumping depletion and nonlinear effects in the electron bunching, the second mechanism is dominant for at the reasonably practical parameters of the pump and the electron beam. It is demonstrated that when using a 100 kW/300 GHz gyrotron as a pump wave source, it is possible to generate a signal tunable in the range from 200 to 205 GHz, with a power exceeding 10 kW. Such a modulator may be of interest for various applications, including hyperfine positronium splitting spectroscopy.

We study the radiation from a small particle bunch with a time-dependent charge, moving in a nondispersive medium. Approximate expressions for the field components, valid in the radiation zone, are obtained for arbitrary time-dependent charge and velocity of the bunch. The energy characteristics of radiation from a time-dependent charge moving at constant velocity are compared with those of radiation from a constant charge undergoing acceleration.

We present a new version of the gyrotron with an axis-encircling beam. In the new gyrotron, unlike the conventional large orbit gyrotron (LOG), non-adiabatic effects are not used to form an axis-encircling helical electron beam. Thus, a conventional magnet with a quasi-dipole field distribution can be employed here. The main feature of the proposed type of gyrotron is the breaking of the azimuthal symmetry of the electron–optical system. This modification can significantly reduce the cost and sizes of the gyrotron setup due to the use of compact magnet systems with a significantly smaller passage hole diameter. The output radiation power of the “compact” gyrotron is sufficient for spectroscopic applications of gyrotrons. Examples of a compact gyrotron with radiation frequencies of 395 and 593 GHz are given.

We present a new design of a multi-beam toroidal cavity containing spiral inductive inserts made of a metamaterial in the region of interaction with the electron beam. It is shown that such a cavity, which operates at the fundamental mode E010, ensures a uniform electric field in a region with a diameter exceeding the wavelength, which is sufficient to accommodate 37 electron beams. In this case, the characteristic impedance per beam is significantly higher than that of the traditional cavity operating at a higher mode. Based on the considered design, the interaction region of a super-powerful multi-beam klystron has been designed, including a cavity tuned to the second harmonic. According to the 1.5-dimensional calculation, the power of the output radiation reaches 39 MW with an efficiency of 64.5% at a current of 19.8 A per beam and an accelerating voltage of 85 kV.