N.G. Borisenko

Regular 3-D networks with clusters for controlled energy transport studies in laser plasma near critical density

Abstract Fabrication methods for low-density fine-structure (cell size < 1 μm) 3-D networks of cellulose triacetate (TAC) are developed. Target densities ranged 4-20 mg/cm3, similar polymer structures were produced both with no load and with high-Z cluster dopant with concentration up to 30%. Foams of varying density down to 0.25 plasma critical density at the third harmonic of iodine laser wavelength are supplied for laser shots. Closed-cell and 3-D network structures are considered and monitored as the means of thermal and radiation control in plasma. In comparative foam-and-foil laser irradiation experiments on PALS (Czech, Prague) laser facility the presently developed TAC targets were used along with earlier reported TMPTA (trimethylol propane triacrilate) and agar foams. Radiation transport and hydrodynamic wave velocities proved to be similar in TAC and TMPTA volume structures both having the form of regular 3-D networks, but differed a lot when TAC was compared to agar foams. Radiation transport during laser pulse in TAC doped with Cu-clusters was faster then in TAC with no dopant, whereas plasma from TAC doped with Cu-clusters cooled down quicker then with no clusters. High-Z cluster dopant is effective tool to control energy transport in underdense plasma.

Plastic Aerogel Targets and Optical Transparency of Undercritical Microheterogeneous Plasma

Abstract The specifications on different low-density structures and high-Z admixtures are compared for target designs used to achieve smoother energy flux from different drivers. The experimentally realized aerogels are studied. Various characterization methods are used taking into account their heterogeneity. The physical processes in such materials under the powerful laser irradiation are discussed, in particular transparency dynamics, plasma homogenization, smoothing capability. The further applications of low-density cellulose triacetate (TAC) in the physical experiments are: possible targets for ns- and for ps-lasers, for EUV sources, EOS targets with low-density layer for pressure increase.

X-RAY TOMOGRAPHY OF GROWING SILICA GEL WITH A DENSITY GRADIENT

Abstract Density gradient laser targets with decreasing density or increasing stepwise density layers were reported in experimental and theoretical papers on astrophysics modeling, equation-of-state (EOS), and shock-wave dynamics studies. The research with targets of smooth density gradient is due. The experiments with gel-catalyst concentration diffusion are discussed for density gradient foam formation. We used multi-image X-ray tomography for measurement of the silica gel layer density gradient in the process of its growth. Gel with a density gradient growing from a flat boundary between a gel-forming solution and a catalyst solution has been investigated through a set of three-dimensional frames of an X-ray computer microtomograph. Laser targets require high (>1 g·cm-3/cm) density gradients of the spatial profile for EOS experiments. The first targets from silica aerogel with a density gradient are demonstrated. Yet these targets perform less density gradient (<0.1 g·cm-3/cm) than is required for pressure multiplication in EOS targets.

Regular Foams, Loaded Foams and Capsule Suspension in the Foam for Hohlraums in ICF

Abstract Many target designs for laser- and ion-driven ICF include foam parts for direct and indirect targets to be investigated in continuing plasma experiments. The freestanding soft foams are described here for comparative plasma experiments. They are pure foam, foam loaded with fine metal dopants or with nanoscale metal seeds. The foams produced and studied have similar fine and regular structure, densities around critical for the third harmonics of Nd-laser and are appropriate for use inside hohlraums. A technique was developed to fill cylinders with such low-density foams and to suspend symmetrically hollow capsules inside.

Laser Targets of Beryllium Deuteride

Abstract Laser targets made of beryllium deuteride BeD2, nanocrystalline beryllium and of low-density beryllium are reported. Spherical laser targets are strong enough and are capable of storing DT-mixture for a long time, compared to that of SiO2 shells.

Aerogel foil plasma: Forward scattering, back scattering, and transmission of laser radiation

Experimental results obtained with “Kanal-2” facility under the study of powerful laser pulse interaction with the low density microstructure media are presented and discussed in this paper. Forward scattering, back scattering, and transmission of laser radiation by aerogel foil plasma have been investigated. The temporal, spectral, and energy characteristics of both the radiation scattering in the direction of heating radiation beam and the back scattering radiation were studied; the directional diagrams of forward and back scattering radiation were obtained for ω 0 and 2ω 0 frequencies. Analysis of intensity redistribution on the heating beam cross-section after passing through a polymer microstructure target was carried out.

Laser-radiation volume absorber and x-ray converter based on low-density beryllium

In the past few years much attention has been paid to studying the laser interaction with low-density polymer sub- critical media formed as the external target layers, which provided more symmetric heating and compression of the target internal shell. Beryllium foam is discussed, as a new type of a low-density media typical of high stability at low specific weight. Moreover, there is a feasibility to produce the beryllium doped by heavy element with its controlled distribution over the deposited layer. The developed technique allows one to use nano-crystal beryllium and low- density beryllium doped by heavy element with its controlled distribution over the deposited layer. The developed technique allows one to use nano-crystal beryllium and low- density beryllium for laser targets.

FABRICATION OF EFFECTIVE LOW-DENSITY CONVERTER OF INTENSIVE LASER RADIATION TO X-RAY AND NOVEL MEASUREMENT METHOD OF LAYER DENSITY FROM HEAVY METAL NANOPARTICLES

Предложен метод измерения плотности слоёв из наночастиц тяжёлых элементов с использованием компьютерного рентгеновского микротомографа, заключающийся в том, что параллельно с нанесением слоя на подложку слой из наночастиц осаждается на стоящий рядом тонкий графитовый стержень — «свидетель». Средний диаметр частиц около 100 нм. При одинаковых режимах работы томографа на эталонных слоях металла измеряется коэффициент пропускания для данного металла. Из полученных коэффициентов пропускания рентгеновских изображений «шапочки» на графитовом стержне определяется эффективная толщина tэф, которая делится на реальную толщину tx и умножается на плотность металла . Эта процедура позволяет определить плотность слоя f = tэф/tx. Наши рентгеновские измерения позволили впервые установить, что плотность слоя наночастиц висмута толщиной около 100 мкм уменьшается по высоте (снизу) от 130 до 80 мг/см. На конференции в Германии нашими студентами была представлена компьютерная программа для обработки рентгеновских изображений «свидетелей» и расчёта плотности слоёв малоплотных металлов. Мишени из малоплотного висмута были использованы в экспериментах на Nd-лазере в Центре атомных исследований в Бомбее, Индия.

Microheterogeneous plasma from polymer aerogel and foam at powerful laser interaction

New results obtained in experiments on laser irradiation (I = 5×1013 W/cm2, λ = 1.054 micrometer) of low-density (10 mg/cm3) fibrous materials (agar and triacetate cellulose) are presented and discussed. The effect of low-density material microstructure of irradiated samples on physical processes in high-temperature plasma was investigated using a variety of plasma diagnostic methods.

From microheterogeneous targets to microheterogeneous plasma—A way to long‐evolution plasma in laser shot

Microheterogeneous targets for plasma investigation are discussed. Microheterogeneity is obtained in the form of metal clusters dispersed inside solid material or foam as well as in the form of metallized aerogel. Microheterogeneous plasma is shown to be initiated by such targets and its behavior is analyzed. The only way to observe the long‐evolution plasma in a short laser experiment is to conserve a certain stage of plasma evolution in the target structure. Target structuring provides: 1) phase separated multi‐ion mixtures in highly non‐ideal plasmas, 2) extended corona (without any prepulse), 3) obscure stability through microinstabilities in the non‐linear growth regime. For ICF applications, underdence microheterogeneous plasma is equalizing the laser irradiation energy over the target‐in‐flight surface.