Cascade klystron self-excited oscillator with delay

Experiments with a new type of resonance microwave self-excited system with complex dynamics, a cascade klystron self-excited oscillator with delayed feedback, are reported. The new self-excited oscillator features a low starting current and many oscillation bands; in addition, it can readily be switched into complex, including random, oscillation modes.     

Photon processes in a strongly magnetized plasma

The photon-scattering process γe ^± → γe ^± is considered in strongly magnetized matter at arbitrary values of temperature and an arbitrary chemical potential. Simple expressions for the absorption coefficients in a strongly magnetized plasma are obtained in two limiting cases, that of a rarefied chargesymmetric plasma and that of a degenerate plasma. Astrophysical applications of the results obtained here are discussed.     

Nonlinear theory of a plasma microwave oscillator using cable waves

The nonstationary problem of excitation of a plasma microwave oscillator of a finite length driven by a pulsed relativistic beam is analyzed. Both analytic and numerical techniques have been used in studying the oscillator dynamics at given beam parameters (configuration, electron energy, and current pulse), with different plasma configurations, and at various lengths of the system. Oscillator characteristics such as the output power, efficiency, and output spectrum have been determined at parameters close to real experimental values. Conditions of optimal oscillator operation have been determined. Zh. éksp. Teor. Fiz. 111, 1258–1273 (April 1997)     

Ionic transitions and oscillator strengths in Debye plasma - a case study

Stability and energy of the excited states of the ion in plasmas are investigated theoretically using the Debye model. The transition energies of and transitions are seen to follow completely opposite trends of variation with the plasma screening strength. The dependence of absorption oscillator strength values on the screening strength is also discussed. Received: 22 October 1997 / Accepted: 9 January 1998     

Cascade processes in inelastic light scattering in ZnSe nanowire structures

The resonance Raman scattering of light in MBE-grown structures with ZnSe nanowires (10–20 nm in diameter) with an Au film deposited on the substrate used as a catalyst was investigated. The thicknesses of the Au layers were 2, 10, and 100 Å. The photon energy of the He-Cd pump laser (λ = 441.6 nm) was in excess of the band gap of bulk ZnSe, and the measurements were conducted at room temperature. Under these conditions, the Raman spectra are defined by a cascade process in which the electron interacting with a longitudinal optical phonon transfers between real band states with a certain probability of radiative recombination at each step. The blue shift of the luminescence maximum associated with the quantum confinement of carriers in the nanowire has been observed. The average nanowire diameter derived from the magnitude of this shift agrees well with electron microscopy measurements.     

Riemann–Liouville and Weyl fractional oscillator processes

Two types of oscillator processes can be obtained as solutions to fractional Langevin equation based on Riemann–Liouville and Weyl fractional integro-differential operators. The relation between these fractional oscillator processes and the corresponding fractional Brownian motion is considered. Generalization of the Weyl fractional oscillator process to positive temperature can be carried out and its partition function can be calculated using the zeta function regularization method.     

Effect of plasma on efficiency enhancement in a high powerrelativistic backward wave oscillator

A linear theory of the excitation of electromagnetic waves in a plasma-filled backward-wave oscillator driven by an intense relativistic electron beam is presented. It is found that the spatial growth rate of backward-wave instability exhibits a resonant increase for a particular value of fill-plasma density. Results are compared to the results of an experiment by K. Minami et al. (1988) on a high-power backward-wave oscillator     

Nonstationary processes in an oscillator with delayed reflection from the load

Nonstationary processes in an oscillator with delayed reflection from a remote load are examined. The case of a large delay, when the number of coexisting stable modes can be large, is given primary consideration. Theoretical analysis of the stability of stationary states (eigenmodes) is carried out. The results of numerical modeling of transient processes during disintegration of unstable states, which show a good agreement with theoretical conclusions, are presented. The possibility of switching between stationary states under a short action of an external control signal is investigated.     

Linear theory of plasma filled backward wave oscillator

An analytical and numerical study of backward wave oscillator (BWO) in linear regime is presented to get an insight into the excitation of electromagnetic waves as a result of the interaction of the relativistic electron beam with a slow wave structure. The effect of background plasma on the BWO instability is also presented.     

Controlling the radiation frequency of a plasma relativistic microwave oscillator during a nanosecond pulse

It is shown experimentally and by numerical simulation that the radiation frequency of a 50-MW plasma relativistic microwave oscillator can be varied within 15% during a 60-ns-wide pulse by varying the plasma concentration. The plasma is generated by pre-ionization of a low-pressure gas. When the degree of ionization increases in a microwave field, the radiation frequency rises. Conversely, when plasma electrons are forced out by the electrostatic field of a high-current relativistic electron beam, the radiation frequency declines. By appropriately selecting the initial gas pressure and degree of gas ionization, one can control both trends and thereby the radiation frequency.     

Cascade processes of energy loss by emission of hard phonons

The method of cascade equations is used for studying the dynamics of the energy loss process (struggling) during passage of particles through a substance. Special attention is paid to multiphoton processes of emission of relativistic electrons in amorphous media and in oriented crystals. New analytic solutions to cascade equations are obtained and a method is developed for solving these equations, which makes it possible to express the results in terms of rapidly converging integrals. It is shown that the relatively simple Landau equation for the energy loss distribution function can be used for analyzing processes of energy loss commensurate with the initial energy of particles. The experimental data for 150-GeV electrons in oriented crystals are thoroughly analyzed.     

Studies in nonlinear stochastic processes. II. The duffing oscillator revisited

We have applied the approximation method of statistical linearization and various higher order corrections thereto to the study of a nonlinear oscillator perturbed by Gaussian, delta-correlated noise. We compute the second-order statistics of the response, i.e., the variances, autocorrelation functions, and spectral densities for various forms of the nonlinearity and compare our results with the few more exact calculations which are available in the literature. We show that a very simple modification of statistical linearization, based upon the use of the variance as obtained from the appropriate Fokker-Planck equation, yields results which are in better agreement with the exact literature results than either statistical linearization or first-order corrections thereto. This modified method of statistical linearization has the significant advantage of great computational simplicity as compared to other attempts of accurate calculations of second-order statistics of nonlinear stochastic equations now in the literature.This work was supported in part by the National Science Foundation under Grants MPS 72-04363 and CHE 75-20624.     

Variation in the radiation frequency of a plasma relativistic microwave oscillator within its nanosecond pulse

The radiation spectrum of a plasma relativistic microwave oscillator with a pulse power of 50 MW operating in the 10-GHz frequency range is studied experimentally. During a 60-ns-long microwave pulse, the radiation frequency may both remain constant and change by more than 1.5 GHz. The pressure of a gas that ionizes in the microwave field has a significant effect on the radiation frequency and thereby changes the concentration of a pregenerated plasma.