Exact value of conjugate ion current in an electrolyte in the Gurevich-Kharkats diffusion-migration model

The exact solution of the problem of ion transport current in an electrolyte in the presence of a conjugate flow of solvent is obtained in the framework of the one-dimensional Gurevich-Kharkats diffusion-migration model; the conditions for the existence of the solution are analyzed.     

Phasing of three vircators simulated in terms of coupled van der Pol oscillators

Phase synchronization in a system of three virtual-cathode microwave oscillators (vircators) simulated by coupled van der Pol oscillators is studied. The phasing dynamics of the vircators is visualized with the phase portraits of the system in the triangular coordinates. Different phasing conditions are found.     

Recirculating Electron Accelerators with Noncircular Electron Orbits as Radiation Sources for Applications (a Review)

State-of-the-art compact recirculating electron accelerators operating at intermediate energies (tens of MeV) are reviewed. The acceleration schemes implemented in the rhodotron, ridgetron, fantron, and cylindertron machines are discussed. Major accelerator components such as the electron guns, accelerating cavities, and bending magnets are described. The parameters of currently operating recirculating accelerators are tabulated, and applications of these accelerators in different processes of irradiation are exemplified.     

Terahertz laser based on optically pumped graphene: Model and feasibility of realization

We consider a terahertz laser based on optically pumped graphene layer and bilayer as the active media and suggested waveguide structure. Using the developed model, we calculate the spectral dependences the dynamic conductivity of the optically pumped graphene layer and bilayer associated with the interband and intraband transitions, estimate the pumping optical power required for lasing, and demonstrate the feasibility of realization of such a laser. The article is published in the original.     

Particle-in-cell simulation of generation of an HF sequence of short current pulses in the vircator with counter-propagating beams

We performed a particle-in-cell (PIC) simulation of a vircator with counter electron beams in a cylindrical cavity with metal walls. Two pairs of counter-propagating superlimiting electron beams with different energy and current in each pair are injected along the cylinder axis. It is found that the electron charge in the cavity is formed as a sequence of pulses corresponding to slow accumulation and fast discharge. It is shown that the pulses are related to the characteristic dynamics of the squeezed beam state, the distributed virtual cathode. This regime can be used to generate anHF sequence of ultrawideband electromagnetic pulses.     

Anomalous characteristics of lasers with a large number of quantum wells

Semiconductor lasers with an active region containing six quantum wells are investigated experimentally. The temperature dependences of working characteristics (threshold current density, external differential quantum efficiency, and directional pattern) are analyzed. Anomalous behavior of the temperature dependence of the threshold current and external differential quantum efficiency, associated with a negative characteristic temperature and a decrease in the quantum efficiency of radiation upon a decrease in temperature, is detected. A narrowing of the directional patterns in the plane perpendicular to the p-n junction upon an increase in temperature is revealed.     

On Dynamics of Metastable Electrons in a Virtual Cathode

We propose a simple model for dynamics of the earlier detected metastable electrons oscillating near a virtual cathode. It was found that their behavior is similar to the dynamics of a reversed pendulum with a vibrating suspension, which was studied by P. L. Kapitsa. The number of metastable electrons is estimated using the method of large particles.     

Principle of charge-mass invariance of motion and possibility of steady-state solitary electrostatic waves in a nearly symmetric plasma

A quasi-neutral nearly symmetric plasma (i.e., a plasma in which particles with opposite charge polarity have identical charge-to-mass ratios but different masses) is considered. The possibility of the existence of steady-state solitary electrostatic waves in such a plasma is proved rigorously. This is associated with violation of the charge-mass invariance principle for a particle moving in a nearly symmetric plasma, which is in turn due to forces (1/n _±)?P _±/?x of a nonelectromagnetic origin.