Features of Fundamental- and Subharmonics ECR Heating in a Magnetic Trap

We compare the efficiency of microwave heating of electrons in a dense plasma at the fundamental harmonics ( = eH/(mc)) and at the subharmonics ( = eH/(2mc)) of the electron gyrofrequency. In particular, recent experimental results showing a higher efficiency of microwave heating at the frequency equal to one half of the electron gyrofrequency are analyzed. Equations describing the nonlinear subharmonic electron cyclotron resonance (ECR) heating are derived for an arbitrary geometry of the microwave field. If the microwave field has the vacuum polarization, then the microwave power absorbed by electrons at the fundamental harmonic of the electron gyrofrequency in rarefied plasmas exceeds by many orders of magnitude the corresponding power absorbed by electrons in the case of nonlinear heating at one half of the electron gyrofrequency. However, it is shown that this difference in a dense plasma does not exceed one order of magnitude, which is explained by the effect of depression of the resonance component of the microwave field. In this case, the efficiency of the formation of high-energy electron population can be influenced not only by the energy-deposition rate but mainly by the stability condition of an electron in the magnetic trap. It is shown that a twofold decrease in the magnetic field, necessary to satisfy the ECR condition at one half of the electron gyrofrequency, leads to a dramatic shortening of the hot-electron lifetime in a magnetic trap and, in turn, to a dramatic decrease in the energy-deposition efficiency. We discuss the dependence of the electron heating on the effect of quasi-static enhancement of the microwave field near a target located in a magnetic trap for the generation of X-ray emission.     

Nature of the N b absorption band in LiF crystals

It was found by the methods of optical spectroscopy and X-ray diffraction analysis that the N _b absorption band in LiF crystals is related to the reoriented F ₄ center when all the F centers lie in the (110) plane. These defects are decomposed into F ₂ centers at annealing.     

Simulation of Gamma-Ray Generation in Interaction of High-Current Ultrarelativistic Particle Beams with Plasma

Optics and Spectroscopy - Formation of hard photons in the process of interaction of high-current ultrarelativistic particle beams with extended plasma targets is analyzed. Dependence of conversion...     

Synthesis and photophysical properties of conformationally fixed tricarbocyanines with phosphonate groups

A method for the synthesis of a series of symmetric and asymmetric conformationally fixed tricarbocyanines was developed based on benzоindolenine containing ethyl phosphonate and diethyl phosphonate groups in the linker at the quaternary nitrogen atom of the indolenine fragment. The polymethine chain meso position was modified by nucleophilic substitution of chlorine with O- and N-nucleophiles. Their absorption and fluorescence spectra were recorded, the possibility of further use of phosphonate-substituted tricarbocyanines as biomarkers was demonstrated. The dark cytotoxicity of synthesized compounds was studied, the possibility of their accumulation in HCT116, MCF7 cancer cells was shown.     

Near QED regime of laser interaction with overdense plasmas

Interaction of laser plulses with intensities up to 10²⁵?W/cm² with overdense plasma targets is investigated via three-dimensional particle-in-cell simulations. At these intensities, radiation of electrons in the laser field becomes important. Electrons transfer a significant fraction of their energy to γ-photons and obtain strong feedbacks due to radiation reaction (RR) force. The RR effect on the distribution of laser energies among three main species: electrons, ions and photons is studied. The RR and electron-positron pair creation are implemented by a QED model. As the laser intensity inreases, the ratio of laser energy coupled to electrons drops while the one for γ-photons reaches up to 35%. Two distinctive plasma density regimes of the high-density carbon target and low-density solid hydrogen target are identified from the laser energy partitions and angular distributions of photons. The power-laws of absorption efficiency versus laser intensity and the transition of photon divergence are revealed. These show enhanced generation of γ-photon beams with improved collimation in the relativistically transparent regime. A new effect of transverse trapping of electrons inside the laser field caused by the RR force is observed: electrons can be unexpectedly confined by the intense laser field when the RR force is comparable to the Lorentz force. Finally, the RR effect and different regions of photon emission in laser-foil interactions are clarified.     

Optimal control with a quadratic criterion in distributed gas-transport systems

On the basis of the method of generalized Lagrange multipliers we obtain optimality conditions in the problem of tracking a given variation in regime of a distributed pipeline gas transport system with an integral quadratic quality criterion. We propose a method and an algorithm for finding optimal controlling actions. We present the results of computation of optimal controls in a homogeneous pipeline. Translated fromDinamicheskie Sistemy, Vol. 11, 1992.