Препринты / Preprints

Cosmic gamma-radiation in the energy range

1-3000 GeVbelongs to the high-energypart of electromagnetic radiation spectrum and is connected with the processes of generation and acceleration in the Universe (pulsars, microquasars, active galactic nuclei, blazars, and so on) and also with the processes of very-high-energycosmic-rayparticle interaction with the matter of the Universe. Cosmic high-energygamma-radiationcan appear as a result of annihilation or decay of Weak Interacting Massive Particles (WIMPs) being dark matter components according to some theoretical models. From the other side, annihilation or decay of WIMPs can lead to the generation of high-energy electrons and positrons, which are supposed to be also detected by the gamma-telescope.

The GAMMA-400 project presents main scientific directions and problems of the project, the state of solving these problems at present, the requirements to the scientific equipment (gamma-ray telescopes), the description of the GAMMA-400 gamma-ray telescope, the requirements to the space complex (spacecraft and ground stations), to scientific data processing, to the analysis and application of scientific results in the science and practice; the schedule of the project realization; the scientific and industrial organizations, participating in the project and their responsibilities.

It is proposed to begin space measurements in 2017.

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Experimental results obtained with «Kanal-2» facility under the study of powerful laser pulse interaction with the polymer low density microstructured media are presented and discussed in the report. The polymer low density microstructure media are considered as promising materials for ICF.

In the experiments the laser radiation parameters were as follows: pulse duration, 2,5 ns; radiation wavelength 1,06 ?m, spectral radiation width, 17 to 42 ?; output laser energy, 30 to 100 J; power flux density of heating radiation on the target, 1013-1014 W/cm2.

The polymer aerogel of triacetate cellulose (TAC) with the density changing within the range of 2-10 mg/cm3 with the thickness 100-500 ?m was used as the target. The interaction with the targets of both the critical and under critical density was investigated.

The temporal, spectral, and energy characteristics of both the radiation scattering in the direction of heating radiation beam and the backscattering radiation were studied; the directional diagrams of forward and backscattering radiation were obtained. Analysis of intensity redistribution on the beam cross-section after passing through a polymer microstructure target was carried out.

The energy balance measurements have shown that the energy transmitted through the target is comparable with that of the incident radiation. The radiation scattered into the aperture of a focusing lens does not exceed 1%. The value of the energy passed through the TAC target depends on the aerogel density, its thickness, and may achieve 70% even when the density proves higher than the critical one. It is found that the spectrum of transmitted radiation is considerably broadened up to 200 ?. The second harmonic generation and other nonlinear effects were also experimentally registered under TAC targets irradiation.

Laser radiation transmission through aerogel is considered as nonlinear transparency of a plasma layer arising from the laser radiation interaction with the low-density target. The observed broadening of the radiation line is connected with the stimulated scattering processes, such as SBS and SRS.

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* Text of the report has been presented at the «4th International Conference on the Frontiers of Plasma Physics and Technology» (Kathmandu, Nepal, 5-10 April 2009).

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The recent experimental results of laser radiation interaction with different targets and their qualitative description are reported. The spectral distribution and the directional diagrams of backscattering radiation on the fundamental and second harmonic frequencies are investigated. The plasma images in visible and near infrared spectral range, in particular, on 2?0, 3/2?0, 5/2?0 and ?0 harmonic frequencies, are registered by means four-frequency polarized microscope. Also the plasma images in the intrinsic X-ray radiation are obtained.

These investigations were carried out with powerful laser installation «Kanal-2», which consists of a neodymium glass laser with controllable function of mutual coherence and an interaction chamber with a complex of diagnostic devices, and allowed to register the parameters of laser radiation and plasma with temporal, spectral and spatial resolution.

An analysis of the experimental data shown, that the reflected energy

makes <_ 1% from the incident radiation energy for all types of the used targets; the plasma electron temperature is ~ 0.5-1.2 keV. Under graphed spatial diagrams of scattered radiation on the frequencies ?o and 2?o it was concluded, that the scattering radiation on the frequency ?o concentrates practically in the heating radiation aperture of the laser beam, the scattering radiation on frequency 2?o spreads more diffusely in space. Intricate structure of plasma radiation spectra on the fundamental frequency and the harmonic frequencies indicate the plasma oscillation excitation in the area of electron density ne<nc, that points out the existence of different types of nonlinear processes under laser-matter interaction.
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* Text of the report has been presented at the «4th International Conference on the Frontiers of Plasma Physics and Technology» (Kathmandu, Nepal, 5-10 April 2009).


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In [1-3] the authors showed that a multimode laser radiation can be effectively transformed into the second harmonic with the help of nonlinear crystals. However, the question of the efficiency of harmonic generation in respect to the number of laser transverse modes at the fundamental frequency remained unanswered. The present report is devoted just to this problem.

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