[en] The energy and time resolutions of a 3.2x3.2x1.0 cm³ BaF₂ scintillator coated with a thin layer of diphenylstilbene wavelength shifter have been measured in comparison to a pure BaF crystal of the same dimensions. The p-p' diphenylstilbene was shown to be an efficient shifter of the ultraviolet light with a slightly better energy resolution. The time resolution measured for Co gamma-rays was degraded from 190 to 360 ps. (orig.)

[en] We have carried out Monte-Carlo calculations of the light collection coefficient τ for different shapes of Zn Se-based scintillators Applying a theoretical model, it has been shown, that the light collection optimization can be reached in scintillators with a geometry where the chaotic light collection is realized. Experimentally it was supported that for detectors of rectangular and cylindrical types with rounded vertexes or edges, the light output increase of up to 20% has been observed, provided the regular light beam dynamics was changed to chaotic. This work has been carried out with support under CRDF Project UE2-2484-KK-02

[en] In May, 1996, we demonstrated the production over a petawatt of peak power in the Nova/Petawatt Laser Facility, generating 620 J in ∼ 430 fs. Results of the first focused irradiance tests, and recent deployment of a novel targeting system will be presented

[en] We report on a proof-of-principle experiment that demonstrates, for the first time, the feasibility of optically injecting electrons into laser-driven plasma waves, first proposed by [D. Umstadter, J.-K. Kim, and E. Dodd, Phys. Rev. Lett. 76, 2073 (1996)]. Using a Table-Top-Tera Watt laser system (I ∼ 5x1018 W/cm2, λ = 1 μm, τ = 400 fs), whose output beam is split by 1:4 ratio into a pump and injection beams, respectively, spatial (within 10 μm) and temporal (within 400 fs) overlap of the two beams were achieved by intersecting them orthogonally in an under-dense (∼ 4x1019 cm-3), supersonically produced He plasma jet. The interference of the two beams in the plasma, produces an intensity grid, directed along the bisector of the their propagation directions. This causes the plasma electrons to be trapped and periodically bunched in the intersection region, reaching modulation densities an order of magnitude higher than that of the cold relativistic plasma wave-breaking limit reported so far, and theoretically estimated. As being bunched in the intersection region, the electrons are stochastically heated to temperatures up to a few 100's of keV. This mechanism cooperates with other possible mechanisms to enhance the temperature, current, and emittance of the electron beam produced by the pump pulse alone. A 2-D PIC code simulation corroborates the reported experimental results. Discussed also, is development of a 100-TW-class Ti:Sapphire laser system for upcoming optical injection experiments in the resonant regime

[en] The role of trapped particles in the destabilization of two-dimensional (2D) current sheets is investigated for applications to theories of magnetospheric substorms. Considering a 2D 'Lembege and Pellat' equilibrium, the linearized gyrokinetic Vlasov-Maxwell equations are solved for electrostatic perturbations with periods close to the typical electron bounce period (τ_be). The particle bounce motion is approximated to its first Fourier component (ω_b=2π/τ_b) which allows the explicit time integration of Vlasov equation and the calculation of the nonlocal particle response. The dispersion equation of the electrostatic bounce modes is derived from the quasineutrality condition. It is shown that the bounce modes exist in a narrow domain of electron-to-ion temperature ratio (T_e/T_i varying from 0.2 to 1.4), with large growth rates (δ∼0.2ω), leading to current sheet destabilization over time scales of 1-2 min.

[en] In the interaction of a 30 fs, 40 TW Ti:sapphire Hercules laser focused to the intensity of 10¹⁹ W/cm² onto a supersonic He gas jet, we observed quasi-monoenergetic electron beams with energy up to 300 MeV and an angular divergence of 10 mrad. We found that the initial plasma density significantly affects the resultant electron beam. For plasma densities ranging between 2*10¹⁹ to 3.5*10¹⁹ cm^-3, quasi-monoenergetic electrons with energies from 80 to 160 MeV and a total charge of about 0.5 nC were produced. Lower plasma densities around 1.5*10¹⁹ cm^-3 produced quasi-monoenergetic electron beams with higher energy, up to (320 ± 50) MeV, but with a decrease of the total charge to about 5 pC. Characterization of the electron beam in terms of the electron's maximum energy, beam divergence and pointing stability is presented. The performed 2-dimensional PIC (particle-in-cell) simulations show the evolution of the laser pulse in the plasma, electron injection, and the specifics of electron acceleration. (authors)

[en] Emulsifiers on the base of tallol and ethanolamines derived acids have been researched in the paper. Electrical stability of emulsions drilling muds has been investigated. It is proved that synthesized emulsifiers according to emulsion stability can be divided into two groups. The first group is emulsifiers with high initial electrical stability but low emulsion stability under long-term storing, and the second group is emulsifiers with low electrical stability but with high emulsion stability. Emulsions flow characteristics have been researched. It is established that emulsifier on the base of ethanolamine provides better emulsion characteristics for drilling muds emulsions

[en] An ablatively driven capillary discharge plasma waveguide has been used to demonstrate guiding of 30 fs, 35 TW laser pulses over distances up to 3 cm with incident intensity in excess of 4x10¹⁸ W/cm². The plasma density range over which good guiding was observed was 1-3x10¹⁸ cm^-3. The quality of the laser spot at the exit mode was observed to be similar to that at the entrance and the transmitted energy was ∼25% at input powers of 35 TW. The transmitted laser spectrum typically showed blueshifting due to ionization of carbon and hydrogen atoms in the capillary plasma by the high intensity laser pulse. The low plasma density regime in which these capillaries operate makes these devices attractive for use in single stage electron accelerators to multi-GeV energies driven by petawatt class laser systems.

[en] It is shown that a formal link relates two-dimensional nonstationary hydrodynamic solutions to the three-dimensional solutions of the magnetostatic equilibrium. This method is used for obtaining new exact analytical solutions of the magnetostatic equilibrium (flux rope type) from known hydrodynamics solutions (point vortex type)

[en] Reduced surface area targets were studied using an ultra-high intensity femtosecond laser in order to determine the effect of electron sheath field confinement on electron dynamics. X-ray emission due to energetic electrons was imaged using a $K_{\mathrm{\alpha <!--\; ??\; -->}}$ imaging crystal. Electrons were observed to travel along the surface of wire targets, and were slowed mainly by the induced fields. Targets with reduced surface areas were correlated with increased hot electron densities and proton energies. Hybrid Vlasov–Fokker–Planck simulations demonstrated increased electric sheath field strength in reduced surface area targets. (paper)