scholarly journals Laser plasma generation and plasma interaction with ablative target

2007 ◽  
Vol 25 (1) ◽  
pp. 53-63 ◽  
Author(s):  
ISAK I. BEILIS
Keyword(s):  
Laser Radiation ◽  
Electron Emission ◽  
Laser Energy ◽  
Plasma Heating ◽  
Target Surface ◽  
Space Region ◽  
Large Contribution ◽  
Plasma Generation ◽  
Plasma Energy ◽  
Electrons And Ions

The model of plasma production by laser radiation onto a solid target was developed taking into account plasma heating by the emitted electrons and target heating by ion bombardment, as well as by the laser radiation. The near target plasma structure was analyzed. The space charge sheath was studied solving the Poisson equation and taking into account the volume charge of accelerated electrons and ions. The kinetics of atoms evaporated from the target and the back-flow of atoms and ions from the plasma towards the surface was analyzed. A system of equations, including equations for solid heat conduction, plasma generation and the plasma expansion was formulated. The calculation for Cu target, laser spot radius 100 μm, pulse duration 1 ms, 103, 10, 1ns and laser power density qL = 10−3–1 GW/cm2 was conducted. The ratio of net evaporation rate to the total evaporated mass flux was determined. It was shown that the plasma mainly generated in the electron emission beam relaxation region and there the plasma flow is subsonic. The electric field at the target surface is relatively large and therefore the ion current to the surface in the space region is large and comparable with the electron emission current. A large contribution of the plasma energy flux in the target heat regime was obtained, showing that the laser generated plasma significantly converts the absorbed laser energy to kinetic and potential energy of the plasma particles, which transport part of the energy through the electrostatic sheath to the solid surface.

scholarly journals Anomalous burning through of thin foils at high brightness laser radiation heating

1999 ◽  
Vol 17 (3) ◽  
pp. 557-563 ◽  
Author(s):  
A.V. KOUTSENKO ◽  
I.G. LEBO ◽  
A.A. MATZVEIKO ◽  
Yu.A. MIKHAILOV ◽  
V.B. ROZANOV ◽  
...  
Keyword(s):  
Laser Radiation ◽  
Flux Density ◽  
High Speed ◽  
Laser Energy ◽  
Theoretical Calculations ◽  
Target Surface ◽  
Thin Foil ◽  
Foil Thickness ◽  
Nanosecond Duration ◽  
Thin Foils

The results of the experiments at the installation “PICO,” with thin foils heating by laser radiation pulses of nanosecond duration are reported. The Al foils with thickness in the range from 3 μ up to 40 μ were used as targets. The flux density was varied from 1013 W/cm2 to 1014 W/cm2. The sharp dependence of the portion of laser energy that passed through the target on foil thickness was observed. This phenomena was accompanied by a relatively small decrease of the passed radiation pulse duration. The anomalously high speed burning through of thin foil was observed in these experiments and the conclusion on the possible mechanism of this phenomena has been done on the base of comparison of experimental data with theoretical calculations. The observed phenomena can be interpreted with a conjecture about the local burning through of a target, in the small areas of the target surface, with many more values of flux density than the average one following laser radiation self-focusing and formation of “hot spots.”

Fast and efficient plasma heating through superelastic laser energy conversion

1980 ◽  
Vol 51 (7) ◽  
pp. 3622-3628 ◽  
Author(s):  
R. M. Measures ◽  
P. L. Wizinowich ◽  
P. G. Cardinal
Keyword(s):  
Energy Conversion ◽  
Laser Energy ◽  
Plasma Heating

scholarly journals Formation of microcrystals under the influence of femtosecond laser radiation on carbon samples in liquid nitrogen

2019 ◽  
Vol 220 ◽  
pp. 02005
Author(s):  
Kirill Khorkov ◽  
Dmitry Kochuev ◽  
Anton Chernikov ◽  
Valery Prokoshev ◽  
Sergey Arakelian
Keyword(s):  
Experimental Study ◽  
Laser Radiation ◽  
Liquid Nitrogen ◽  
Subsurface Layer ◽  
Laser Action ◽  
Target Surface ◽  
Femtosecond Laser Radiation ◽  
Carbon Target ◽  
Direct Laser ◽  
Temperature And Pressure

In this paper, we present the results of an experimental study of the carbon microcrystals formation by direct laser action on the carbon target surface at temperature of liquid nitrogen. It is demonstrated that the formation of microcrystals occurs in the subsurface layer and is caused by the achievement of critical temperature and pressure.

Three-Dimensional Numerical Simulation and Experimental Study of Sheet Metal Bending by Laser Peen Forming

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Yongxiang Hu ◽  
Yefei Han ◽  
Zhenqiang Yao ◽  
Jun Hu
Keyword(s):  
Numerical Model ◽  
Sheet Metal ◽  
Laser Energy ◽  
Three Dimensional ◽  
Target Surface ◽  
Thick Sheet ◽  
Specimen Thickness ◽  
Forming Process ◽  
Form Complex ◽  
Peen Forming

Laser peen forming (LPF) is a purely mechanical forming method achieved through the use of laser energy to form complex shapes or to modify curvatures. It is flexible and independent of tool inaccuracies that result from wear and deflection. Its nonthermal process makes it possible to form without material degradation or even improve them by inducing compressive stress over the target surface. In the present study, a fully three-dimensional numerical model is developed to simulate the forming process of laser peen forming. The simulation procedure is composed of several steps mainly including the shock pressure prediction, the modal analysis, and the forming process calculation. System critical damping is introduced to prevent unnecessary long post-shock residual oscillations and to greatly decrease the solution time for simulation. The bending profiles and angles with different thicknesses are experimentally measured at different scanning lines and scanning velocities to understand the process and validate the numerical model. The calculated bending profiles and angles agree well with the trend of the measured results. But it is found that simulations with the Johnson–Cook model are more consistent, matching the experimental results for the thick sheet metal with a convex bending, while the elastic-perfectly-plastic model produces a better agreement even though with underestimated values for the thinner sheet metal with a concave bending. The reason for this phenomenon is discussed, combining the effects of strain rate and feature size. Both the simulation and the experiments show that a continuous decrease in bending angle from concave to convex is observed with increasing specimen thickness in general. Large bending distortion is easier to induce by generating a concave curvature with LPF, and the angle of bending distortion depends on the number of laser shocks.

scholarly journals Efficiency of electron beam extraction to the atmosphere in an accelerator based on ion-electron emission

2021 ◽  
Vol 2064 (1) ◽  
pp. 012116
Author(s):  
S Yu Doroshkevich ◽  
M S Vorobyov ◽  
M S Torba ◽  
N N Koval ◽  
S A Sulakshin ◽  
...  
Keyword(s):  
Electron Beam ◽  
Electron Emission ◽  
Ambient Atmosphere ◽  
Beam Extraction ◽  
Periodic Mode ◽  
Extraction Coefficient ◽  
Plasma Generation ◽  
Average Value ◽  
Generation Mode ◽  
Discharge Parameters

Abstract The use of a modern element base makes it possible to create power supplies with a transition from a direct mode of generation of an auxiliary discharge to a pulse-periodic mode with a pulse repetition rate at the level of several tens of kHz. This allows for a more flexible adjustment of the discharge parameters, keeping the average value of its current, but changing its amplitude with a corresponding change in the pulse duty cycle. In this work, using an electron accelerator based on ion-electron emission, generating a wide-aperture electron beam, we research the effect of auxiliary discharge generation mode (direct and pulse-periodic) on the efficiency of electron beam extraction into the ambient atmosphere. It is shown that, in a direct mode of electron beam generation at an accelerating voltage of 150 kV, the beam extraction coefficient does not exceed 0.25. The possibility of increasing the extraction coefficient to K = 0.55 at the same accelerating voltage of 150 kV was demonstrated without making changes to the design of the accelerator, but switching to a pulsed-periodic mode of emission plasma generation.

scholarly journals Influence of the Distance between Focusing Lens and Target Surface on the Characteristics of Laser-excited Lead Plasma

2021 ◽  
pp. 4694-4701
Author(s):  
Qusay Adnan Abbas
Keyword(s):  
Electron Temperature ◽  
Pulse Laser ◽  
Electron Number Density ◽  
Laser Energy ◽  
Pulse Length ◽  
Target Surface ◽  
Spectral Lines ◽  
Stark Broadening ◽  
Number Density ◽  
Electron Number

      The present work investigated the effect of distance from target surface on the parameters of lead plasma excited by 1064nm Q-switched Nd:YAG laser. The excitation was conducted in air, at atmospheric pressure, with pulse length of 5 ns, and at different pulse laser energies. Electron temperature was calculated by Boltzmann plot method based on the PbI emission spectral lines (369.03 nm, 416.98 nm, 523.48, and 561.94 nm). The PbI lines were recorded at different distances from the target surface at laser pulse energies of 260 and 280 mJ. The emission intensity of plasma increased with increasing the lens-to-target distance. The results also detected an increase in electron temperature with increasing the distance between the focal lens and the surface of the target in all laser energies under study. In addition, the electron number density was determined by using the Stark broadening method. The data illustrated that the electron number density was increased with increasing the distance from target surface, reaching the maximum at a distance of 11 cm for all pulse laser energy levels under study.

COHERENT ANTI-STOKES RAMAN SCATTERING AND FLUORESCENT STUDY OF IGNITION AND COMBUSTION OF H2/O2 MIXTURES UPON PHOTODISSOCIATION OF O2 MOLECULES

2020 ◽  
Author(s):  
K. A. Vereshchagin ◽  
◽  
S. Yu. Volkov ◽  
V. D. Kobtsev ◽  
S. A. Kostritsa ◽  
...  
Keyword(s):  
Laser Radiation ◽  
Low Temperature ◽  
Raman Scattering ◽  
Combustion Chamber ◽  
Laser Energy ◽  
Diagnostic Techniques ◽  
Oh Radicals ◽  
Ignition And Combustion ◽  
193 Nm ◽  
Anti Stokes

The low-temperature ignition of H2/O2 mixture promoted by resonant laser radiation leading to the photodissociation of O2 molecules was studied experimentally. The experimental test bench involving the model combustion chamber, coherent anti-Stokes Raman scattering (CARS) and fluorescent diagnostic techniques was created for the experimental investigation of mixture ignition and combustion at conditions typical for gas turbine engines. For the production of chemically active oxygen atoms which initiate ignition in the H2/O2 mixture, the pulsed excimer ArF-laser emitting at a wavelength of 193 nm was employed. Complementary experiments on measuring the temperature and recording the emission of OH and OH* radicals indicate that it is possible to ignite the H2/O2 mixture with ф = 1-3 and P0 = 1-3 atm at a rather low temperature of ~ 700 K under the action of focused laser radiation (A = 193 nm) with the energy in the laser pulse of E = 30-150 mJ. The induction time varies in the range of 8-50 s depending on the laser energy and mixture parameters. Two-dimensional (2D) numerical simulation of ignition and combustion processes in the model combustion chamber was performed. A good agreement of calculation results with experimental data was obtained.

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