Engineering topics

Bychenkov, V Yu

Publications and source records attributed to Bychenkov, V Yu.

11 records

DOE OSTI2016

Target optimisation for the yield of X-rays of desired hardness under femtosecond pulse irradiation

Different regimes of electron acceleration from solid foils and low-density targets are investigated using three-dimensional numerical simulations. The size of the plasma corona is shown to be the main parameter characterising the temperature and number of hot electrons, which determine the yield of X-ray radiation and its hardness. Also studied is the generation of X-ray radiation by laseraccelerated electrons, which bombard the converter target located behind the laser target. (extreme laser radiation: physics and fundamental applications)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

Laser vacuum acceleration of a relativistic electron bunch

With regard to the problem of laser acceleration of a relativistic electron bunch we present a scheme of its vacuum acceleration directly by a relativistic intensity laser pulse. The energy of the electron bunch injected into the laser pulse leading edge increases during its coaxial movement to a thin, pulse-reflecting target. The laser-accelerated electrons continue to move free forward, passing through the target. The study of this acceleration scheme in the three-dimensional geometry is verified in a numerical simulation by the particle-in-cell method, which showed that the energy of a part of the electrons can increase significantly compared to the initial one. Restrictions are discussed, which impose limiting values of energy and total charge of accelerated electrons. (superstrong light fields)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Effect of a short weak prepulse on laser-triggered front-surface heavy-ion acceleration

A suppression of light-ion acceleration (from surface water contaminants) was observed when a moderate-intensity subpicosecond laser pulse was focused on a thick metal target. Simultaneously, an effective generation of high-energy multicharge ions of the target material (Fe) was experimentally observed. A numerical simulation based on the Boltzmann-Vlasov-Poisson model revealed that this is due to the very specific regime of cleaning contaminants from the target surface by the short weak prepulse preceding the main pulse by more than 10 ns and having an intensity below the surface breakdown threshold. Because this prepulse causes the contaminant layer to boil explosively, a low-density gap forms above the target surface. These conditions are consequently favorable for boosting the energy of heavy ions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Laser-driven relativistic electron beam interaction with solid dielectric

The multi-frames shadowgraphy, interferometry and polarimetry diagnostics with sub-ps time resolution were used for an investigation of ionization wave dynamics inside a glass target induced by laser-driven relativistic electron beam. Experiments were done using the 50 TW Leopard laser at the UNR. For a laser flux of {approx}2 Multiplication-Sign 10{sup 18}W/cm{sup 2} a hemispherical ionization wave propagates at c/3. The maximum of the electron density inside the glass target is {approx}2 Multiplication-Sign 10{sup 19}cm{sup -3}. Magnetic and electric fields are less than {approx}15 kG and {approx}1 MV/cm, respectively. The electron temperature has a maximum of {approx}0.5 eV. 2D interference phase shift shows the 'fountain effect' of electron beam. The very low ionization inside glass target {approx}0.1% suggests a fast recombination at the sub-ps time scale. 2D PIC-simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Generation of a quasi-monoergetic proton beam from laser-irradiated sub-micron droplets

Proton bursts with a narrow spectrum at an energy of (2.8 {+-} 0.3 MeV) are accelerated from sub-micron water spray droplets irradiated by high-intensity ({approx}5 Multiplication-Sign 10{sup 19} W/cm{sup 2}), high-contrast ({approx}10{sup 10}), ultra-short (40 fs) laser pulses. The acceleration is preferentially in the laser propagation direction. The explosion dynamics is governed by a residual ps-scale laser pulse pedestal which 'mildly' preheats the droplet and changes its density profile before the arrival of the high intensity laser pulse peak. As a result, the energetic electrons extracted from the modified target by the high-intensity part of the laser pulse establish an anisotropic electrostatic field which results in anisotropic Coulomb explosion and proton acceleration predominantly in the forward direction. Hydrodynamic simulations of the target pre-expansion and 3D particle-in-cell simulations of the measured energy and anisotropy of the proton emission have confirmed the proposed acceleration scenario.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Femtosecond laser-plasma interaction with prepulse-generated liquid metal micro-jets

Ultra-short laser pulse interaction with a micro-structured surface of a melted metal is a promising source of hard X-ray radiation. Micro-structuring is achieved by a weak prepulse which produces narrow high density micro-jets. Interaction of the main laser pulse with such jets is shown to be a 100 times more efficient X-ray source than ordinary metal targets. This paper presents the results of optical and x-ray studies of laser-plasma interaction physics under such conditions supported by numerical simulations of fast electron generation.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2012

Ionization-assisted relativistic electron generation with monoenergetic features from laser thin foil interaction

The concept of ionization-induced injection into the laser pulse to produce quasi-monoenergetic bunches of electrons from ultra-thin solid dense targets is analyzed. When the laser pulse propagates through semi-transparent foil the electrons from inner atom shells remain bound during the rise time of the laser pulse and are ionized by the laser intensity near its maximum amplitude, which satisfies the best injection condition for subsequent acceleration. It was found that a bunch of quasimonoenergetic electrons from inner atom shells moves co-directionally with laser pulse and acquire energy {approx}m{sub e}c{sup 2}a{sup 2}/2.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

High-energy protons from submicron-sized targets

Improving of intensity contrast ratio of intense short laser pulses is making it possible to use submicron-sized targets, both spherical and plane, in the interest of proton acceleration for different applications. The way of improving of the ion beam quality is utilization of targets with two ion species - heavy ions (majority) and light ions, e.g. protons, (minority). Two different approaches, analytical theory and particle-in-cell simulations (PIC) are presented for studying the characteristics of laser-triggered ions due to the Coulomb-like mechanism of particle acceleration from submicron-sized targets. The comparative analysis of explosions of heterogeneous (layered) and homogeneously mixed targets for production of best quality ion bunches has been performed. We also found the regime of anisotropic proton acceleration from spherical targets with light and heavy ions relevant to the experiments with submicron-diameter droplets from water spray target irradiated by an ultrashort intense laser pulse.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

Femtosecond laser-plasma interaction with prepulse-generated liquid metal microjets

Ultrashort laser pulse interaction with a microstructured surface of a melted metal is a promising source of hard x-ray radiation. Microstructuring is achieved by a weak prepulse that produces narrow high-density microjets. As an x-ray source, the interaction of the main laser pulse with such jets is shown to be nearly two orders of magnitude more efficient than the interaction with ordinary metal targets. This paper presents the results of optical and x-ray studies of laser-plasma interaction physics under such conditions supported by numerical simulations of microjet formation and fast-electron generation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

New solutions in the theory of self-focusing with saturating nonlinearity

On the basis of an approximate analytic solution of a Cauchy problem for a nonlinear Schroedinger (NLS) equation describing steady-state light beams in a medium with saturating nonlinearity by the method of renormgroup (RG) symmetries, a classification of self-focusing solutions is given depending on two control parameters: the relative contributions of diffraction and nonlinearity and the saturation strength of the nonlinearity. The existence of tube-type self-focusing solutions is proved for an entering beam with Gaussian radial distribution of intensity. Numerical simulation is carried out that allows one to verify the theory developed and to determine its applicability limits.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

Fountain effect of laser-driven relativistic electrons inside a solid dielectric

Ultrafast interferometry with sub-ps resolution has been applied for the direct measurement of an electron density induced by a laser-driven relativistic electron beam inside a solid dielectric. The topology of the interference phase shift shows the signature of the ''fountain effect,'' a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields. The very low ionization, {approx}0.1%, observed after the heating pulse suggests a fast recombination at the sub-ps time scale.

36 MATERIALS SCIENCE↗