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Porous materials have many applications for laser–matter interaction experiments related to inertial confinement fusion. Obtaining new knowledge about the properties of the laser-produced plasma of porous media is a challenging task. In this work, we report, for the first time to the best of our knowledge, the time-dependent measurement of the reflected light of a terawatt laser pulse from the laser-produced plasma of low-Z foam material of overcritical density. The experiments have been performed with the ABC laser, with targets constituted by foam of overcritical density and by solid media of the same chemical composition. We implemented in the MULTI-FM code a model for the light reflection to reproduce and interpret the experimental results. Using the simulations together with the experimental results, we indicate a criterion for estimating the homogenization time of the laser-produced plasma, whose measurement is challenging with direct diagnostic techniques and still not achieved.
The generalized theory of terawatt laser pulse interaction with a low-dense porous substance of light chemical elements including laser light absorption and energy transfer in a wide region of parameter variation is developed on the base of the model of laser-supported hydrothermal wave in a partially homogenized plasma. Laser light absorption, hydrodynamic motion, and electron thermal conductivity are implemented in the hydrodynamic code, according to the degree of laser-driven homogenization of the laser-produced plasma. The results of numerical simulations obtained by using the hydrodynamic code are presented. The features of laser-supported hydrothermal wave in both possible cases of a porous substance with a density smaller and larger than critical plasma density are discussed along with the comparison with the experiments. The results are addressed to the development of design of laser thermonuclear target as well as and powerful neutron and X-ray sources.
The dynamics of fast laser-induced vacuum discharge, with a rather
small value of amplitude of current (≤ 10 kA), as well as the voltage
and energy of the capacitor bank (≤ 20 kV and 20 J, respectively), have
been investigated. It has been experimentally demonstrated that the
initiations conditions determined by the energy and duration of the laser
radiation, fundamentally determine the dynamics of the discharge. Two
types of space and time separated plasma instabilities are revealed. It
was found that the first of instabilities occurs at the initial stage of
the discharge and is caused by a pinch structure, which takes place in
front of a cathode jet extending in vacuum. The second type of
instabilities arises at the top or recession of the current and is
accompanied by the generation of hard (energy ≥100 keV) bremsstrahlung
X-ray radiation from the anode area. The excess energy of the hard
components of radiation over the potential of the current source is
associated with the effects of plasma-erosive breaking.
An investigation of a monochromatic point X-ray
source of photon energy ∼5 keV was carried out. The
source was set up using a laser produced Al plasma as a
cathode and a point-tip Ti anode. Optimum parameters of
the diode were determined from experimental measurements
of X-ray intensity dependence on laser pulse energy, applied
accelerating voltage, and distance between target (cathode)
and anode, using Nd:glass laser pulses (FWHM 30 ns) of
2 mJ to 4 J energy. Electron temperature characterization
of the target plasma was also performed from the XUV emission
spectrum (5–80 Å). Parameters of X radiation
in Ti K-shells are (1) spectral brightness of
(2) spatial size ∼300 microns, and (3) X-ray pulse
duration less than 20 ns.
Experimental study of the radiation scattered at the laser
heating of low-density foam targets and transmitted through
the targets is presented. The scattered and transmitted
radiations were investigated using spectrometers and streak
cameras providing spatial, angular, spectral and temporal
resolutions that enabled us to study the dynamics of the
process of burning-through of the thick foam targets, the
velocities of the plasma critical density motion as well
as mass velocity of the plasma.
Results of experimental and computational investigations devoted to energy transfer mechanisms and X-ray conversion efficiency in laser-produced plasma are presented and discussed. The layers of different thicknesses and diameters deposited on the plane mylar substrate were irradiated by the focused beam of Nd:glass laser. Spectrally, temporally, and spatially resolved measurements of soft X-ray emission have been carried out at power densities of 1013-1014 W/cm2. The conditions of “re-emission” zone formation have been established. Radiative heat conductivity is shown to be the important energy transfer mechanism in the experimental conditions under investigation.
The present review is of the experimental investigations on laser-plasma interaction being carried out in past years at IAE. Experiments were conducted on the “Mishen” facility. The laser system of Mishen consists of two channels with output beam parameters as follows: the main beam—output energy 100–200 J (λ = 1.054 μm) in 3-ns pulse, divergence ∼2 × 10-4 rad, contrast ratio ∼106, power density at the target surface ∼1013–1014 W/cm2; the diagnostic beam–output energy 10–20 J (λ = 1.054 μm) and 5–10 J (λ = 0.53 μm) in 0.3-ns pulse, divergence ∼10-4 rad, power density 1013 - 1014 W/cm2. Our aim in this experiment is to study the different aspects of the ICF processes in flat geometry. The main issues of our studies are hydrodynamic aspects, including acceleration efficiency, high-velocity impact in cascade targets, hydrostability, and X-ray physicsconversion efficiency, heat transfer, and X-ray-driven targets.
X-ray emission from planar targets irradiated by 1.054-μm laser pulses was observed with temporal, spatial, and spectral resolution. The main purpose of these measurements was the investigation of energy transfer in multilayer targets and X-ray conversion efficiency. A mass ablation rate was determined from temporal analysis of multicharged ion line emission and a key role of corona X-ray emission in accelerated material preheating was established.
A program is under way to develop methods and instrumentation based on charge-coupled device (CCD) sensors for hot plasma diagnostics. We have developed a new X-ray spectrometer in which a freestanding X-ray transmission grating is coupled to a CCD linear array detector with electronic digitized readout replacing film and its wet processing. This instrument measures time-integrated pulsed X-ray spectra with moderate spectral resolution (δλ ≤ 0.6 nm) over a broad spectral range (0.3–2 keV) with high sensitivity, linearity, and large dynamic range. The performance of the device was tested using laser plasma as the X-ray source.
Scattered emission from the laser plasma created in shell target heating experiments using the Delfin-1 laser has been studied. It is shown that the ω0 spherical harmonics can be used to determine both the plasma temperature in the nc/4 region and also the plasma flow through this region.
We have developed a new soft x-ray spectrometer covering the photon energy range 50–500 eV. It employs a free-standing transmission grating coupled to a microchannelplate detector. The performance of the device was tested by using radiation from a synchrotron with a continuous spectrum. The detector shows a rather flat response over most of the useful spectral range, with an abrupt decrease in the sensitivity at the short-wavelength end. Its simplicity of operation makes the device attractive for such applications as the study of soft x-ray emission from laser-produced plasmas.
This paper presents the results of laser-produced plasma investigations at an intensity of 1014W/cm2. Shadowgraphy, interferometry and second harmonic emission measurements were done to evaluate the main hydrodynamic parameters of the plasma.
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