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The current-voltage characteristic of a thin organic layer located between conductive electrodes is analytically modeled. To this end, a theoretical model is developed which considers not only the interaction of an injected carrier with its mirror charge “reflected” in the nearest electrode, but also the effect of multiple reflections and the injection current from the opposite electrode. The current-voltage characteristics at various temperatures and barrier heights are compared to the model previously developed by Arkhipov et al. The limits of applicability of this model are determined. At low temperatures and voltages, the effect of multiple reflections becomes significant, which cause an increase in the current. These results should be considered when testing individual thin layers constituting multilayer organic light-emitting diodes.

A relatively simple analytical model taking into account energy disorder and space charge effects is proposed for calculating the current-voltage characteristics for the monopolar regime of charge transfer in thin layers of disordered organic materials. The dependence of the minimal energy barrier height for injection, for which the space charge effects can be disregarded, is determined as a function of the layer thickness and the Gaussian energy distribution width.

Using the mathematical model of electron beam transformation in a narrow tube developed by the authors and the KlypWin program suite, conditions for the maximal efficiency of decimeter-wave klystrons having from three to six amplification stages are simulated. Simulation is based on a real electron-optical system and real parameters of the cavities. It is shown that the maximal efficiency (across the load) is 83% for a four-cavity klystron, 86% for a five-cavity klystron, 88% for a six-cavity klystron, and 90% for a seven-cavity one. The electronic efficiency of the simulated seven-cavity klystron equals 94%, which implies the achievement of a global extremum.

The dependence of the maximal efficiency on the amplification factor is studied for double-cavity klystrons simulated based on real electron-optical systems and real electrodynamic parameters of cavities. Simulation uses a mathematical model of electron beam transformation in a narrow tube and a KlypWin software suite. It is shown that the maximal efficiency of such klystrons, 46–47%, is achieved at an amplification factor of 16–18 dB.

The problem of transformation of an electron beam in a long narrow conducting tube is considered. General wave solutions for the propagation of an arbitrary (including aperiodic) modulation of a homogeneous beam are obtained in the case of weak modulation. The solution corresponding to harmonic modulation is compared to the solutions obtained earlier and described in the literature. The problem of beam transformation corresponding to the bunching regime in high-power klystrons is also considered (including overtaking). A discrete analytic solution to the problem is obtained in the “frozen beam approximation.” This solution is tested for the problem of spilling of a monovelocity bunch and for the problem of the efficiency of a two-cavity klystron with infinitely narrow gaps. In both cases, physically correct results are obtained.

This article, based on the paper “Problems of Modern Nuclear Physics and Training of Nuclear Power Plant Personnel,” which was heard at a meeting of the RAS Presidium, discusses major research guidelines in fundamental physics using large accelerators. The author gives a list of problems and phenomena, the essence of which cannot be described within the conventional Standard Model. In order to understand them, in the author’s opinion, we need a new level of accelerator energies and greater measurement accuracy.

The diffraction radiation at the frequency that is close to the natural resonance of the medium is considered for a fast charged particle that passes in the vicinity of a dielectric wedge. The dependence of the angular distribution of the diffraction radiation on the angle between the wedge faces and on the energy of the ultrarelativistic particle is analyzed.

The effect of an external field on the transition radiation from an ultrarelativistic particle is considered at grazing emission angles. The angular and frequency distribution of transition radiation is found. It is shown that the external field substantially increases the angular asymmetry of transition radiation at grazing emission angles.

Diffraction radiation of a charged ultrarelativistic particle passing near the edge of a target of finite width and thickness is considered. A solution is derived for the frequencies higher than that of plasma. It is shown that the spectral density of the radiated energy for high-energy particles ranges to higher-than-plasma frequencies. An estimation of the total radiation loss is made.

We present a time-resolved infrared (IR) pump and extreme-ultraviolet (XUV) probe diffraction experiment to investigate ultrafast structural dynamics in colloidal crystals with picosecond resolution. The experiment was performed at the FLASH facility at DESY with a fundamental wavelength of 8 nm. In our experiment, the temporal changes of Bragg peaks were analyzed and their frequency components were calculated using Fourier analysis. Periodic modulations in the colloidal crystal were localized at a frequency of about 4-5 GHz. Based on the Lamb theory, theoretical calculations of vibrations of the isotropic elastic polystyrene spheres of 400 nm in size reveal a 5.07 GHz eigenfrequency of the ground (breathing) mode., 12 pages, 3 figures

The asymmetry of parametric x rays emitted by polarized electrons is considered on the basis of quantum theory. The asymmetry value is calculated for emission both in the Bragg direction and in directions different from the Bragg direction by an angle of order γ−1. The asymmetry is computed for the longitudinal and for the transverse polarization of the electrons.

A new type of bent crystal-assisted radiation is analyzed as an interference process of synchrotron and undulator radiation. As the bending radius grows ( R → ∞) the corresponding formulas are transformed into the ones for channeling radiation in a straight crystal. Dipole and synchrotron-like radiation are investigated.

Expressions for the intensity of specific radiation accompanying the deflection of high-energy particles by a bent crystal are presented. It is shown that when R ∞ (R is the bending radius) the corresponding formulas are transformed into those for channeling radiation in an unbent (straight) crystal. Dipole, synchrotron-like radiation, and polarization effects are analysed. Numerical calculations of the radiation and polarization in the bent planes using a realistic potential are made for beams with different parameters. Es werden Ausdrucke fur die Intensitat von Strahlungen angegeben, die die Ablenkung von hochenergetischen Teilchen durch einen gebogenen Kristall begleiten. Fur R ∞ (R ist der Biegeradius) gehen die entsprechenden Formeln in diejenigen fur Kanalstrahlung in einem nichtgebogenen Kristall uber. Es werden Dipol- und Synchrotron-artige Strahlung sowie Polarisationseffekte untersucht. Numerische Rechnungen zu Strahlung und Polarisation unter Verwendung eines realistischen Potentials fur die gebogenen Gitterebenen werden fur Strahlen mit unterschiedlichen Parametern durchgefuhrt.

The kinetic equations are derived which describe the energy loss for fast charged particles with account for their correlated motion in the field of atomic planes and multiple scattering. The numerical calculations for relativistic proton beams demonstrate that for large beam incident angles θ0 > θL (where θL is the Lindhard angle) the energy loss distributions coincide with the Landau theory with good accuracy. At small incidence angles θ0 < θL of a narrow positively charged particle beam the distribution maximum is shifted to anomalously small energy losses. The problem of particle selection according to the small energy loss criterion is considered. A comparison between the theory and experiment is made. Die kinetischen Gleichungen, die den Energieverlust fur schnelle geladene Teilchen beschreiben, werden unter Berucksichtigung ihrer Korrelationsbewegung im Feld der Atomebenen und Vielfachstreuung abgeleitet. Die numerischen Berechnungen fur relativistische Protonenstrahlen zeigen, das fur grose Einfallswinkel θ0 > θL (wobei θL der Lindhard-Winkel ist) die Energieverlustverteilung mit guter Genauigkeit mit der Landau-Theorie ubereinstimmt. Bei geringen Einfallswinkeln θ0 < θL eines schmalen positiv geladenen Teilchenstrahls ist das Verteilungsmaximum zu anomal geringen Energieverlusten verschoben. Das Problem der Teilchenselektion wird entsprechend dem Kriterium fur geringen Energieverlust behandelt. Ein Vergleich zwischen Theorie und Experiment wird durchgefuhrt.

The determination of magnitudes of basic parameters of the high energy elastic scattering amplitude are examined at small momentum transfers with taking account of the Coulomb-hadron interference effects., 6 pages, LaTeX, 4 figures (files.ps), Talk at the International Workshop "Spin and Symmetry" (Prague, Chech., 13-19 July 2000)

There are suggestions to extract the pp total cross section, σT(pp), at polarized colliders by measuring the analyzing power, AN(t), or so called the factor of merit, M(t)=AN2(t)dσ/dt. This talk is devoted to a detailed study of these new concepts.There are suggestions to extract the pp total cross section, σT(pp), at polarized colliders by measuring the analyzing power, AN(t), or so called the factor of merit, M(t)=AN2(t)dσ/dt. This talk is devoted to a detailed study of these new concepts.

This paper presents kinetic equations for radiative energy losses and for the selfpolarization of a high energy beam taking into account multiple scattering in a bent plane potential. The numerical calculations have been carried out for TeV energy lepton beams.

An analysis is made of the current status of investigations of ? radiation emitted by channeled relativistic charged particles in single crystals. It is shown that the spectral and angular distributions of radiation emitted by channeled particles differ significantly from the corresponding distributions in the case of familiar coherent bremsstrahlung in crystals and they appear as a result of radiative transitions of a particle between different levels (bands) of the transverse motion. It is shown that by increasing the energy of the incident particle, it should be possible to obtain an emitted frequency in the x-ray and ? ranges as a result of the Doppler effect. Possible methods of amplifying ? radiation in a crystal are discussed. An analysis is made of stimulated radiation and the lasing threshold value of the particle current density is given.

The theory of coherent elastic scattering of fast positively charged particles in a single crystal is presented. The interaction of fast positively charged particles with the crystallographic atomic row is investigated in detail when the incident-particle momentum is parallel to the crystallographic axis. The differential and total scattering crossections are obtained. The dependence of the total scattering crosssection on the length of the atomic string is examined.

In this work the behavior of the characteristics of the volume charge induced by a ..gamma..-ray pulse in a thick plane-parallel plate, under the normal incidence of a beam of monoenergetic quanta ranging from 10 keV to 1 MeV, is examined. The theoretical results obtained are compared with experimental data obtained for a layer of polymethyl methacrylate 1.8 mm thick with the use of the spectrum of x-ray bremmstrahlung, produced by 1 MeV electrons passing through an iron target with a specific thickness of 0.796 g/cm/sup 2/. The density distribution of the volume charge was obtained taking into account in detail the angular characteristics of the photo- and Compton electrons. A simple procedure was used to take into account the effect of multiple scattering of the electrons; unlike well-known computational methods it enabled clear physical interpretation and did not require large amounts of computer time in carrying out the calculations.