A.I. Gromov

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.

Nonequilibrium laser-produced plasma of volume-structured media and ICF applications

This paper is devoted to the investigation of powerful laser pulse interaction with regularly and statistically volume-structured media with near critical average density and properties of laser-produced plasma of such a media. The results of the latest experiments on laser pulse interaction with plane foam targets performed on Nd-laser facilities ABC in the ENEA-EURATOM Association (Frascati, Italy) and MISHEN in the Troitsk Institute of Innovation Thermonuclear Investigations (TRINITI, Troitsk Russia), and J-laser ISKRA-4 in the Russian Federal Nuclear Center, All-Russian Scientific Research Institute of Experimental Physics (RFNC-VNIIEF, Sarov, Russia) are presented and analyzed. High efficiency of the internal volume absorption of laser radiation in the foams of supercritical density was observed, and the dynamics of absorbing region formation and velocity of energy transfer process versus the parameters of porous matter are found. Some inertial confinement fusion (ICF) applications based on nonequilibrium properties of laser-produced plasma of a foam and regularly structured media such as the powerful neutron source with yield of 10 9 -10 11 DT-neutrons per 1 J of laser energy, laser-produced X-ray generation in high temperature supercritical plasma, and the compact ICF target absorbers providing effective smoothing and ablation are proposed.

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.

Thermal Smoothing by Laser-Produced Plasma of Porous Matter

Efficient energy transfer and smoothing effect in laser-irradiated polystyrene foam targets have been observed in preliminary experiments on the PALS iodine laser facility. A theory of laser light absorption region formation and ablation pressure generation in laser-produced plasma of porous matter has been developed and applied for discussion of the results obtained. In particular, two stages of homogenization of the porous matter, important for comprehension of the anomalously high absorption of laser radiation in supercritical foam matter, have been identified: the first, a considerably fast stage of partial homogenization, followed by a much slower second stage, leading to a uniform medium.

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.

Novel Technologies in Microfusion

The developed method of foaming for spherical shells made from metastable hydrides such as BeD2 or ND3BD3 is discussed. The importance of low‐density state of meta‐stable hydrides due to the higher energy transfer rates is discussed. The properties of fuel — materials with high content of hydrogen isotopes, which have substantial importance for large fusion target fabrication technology and neutron generation in strong e.m. fields are analyzed. New laser targets and their characteristics are demonstrated.

Intensive (up to 1015 W/cm2) Laser Light Absorption and Energy Transfer in Subcritical Media with or Without High‐Z Dopants

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/cc, 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. Experiments with underdense foam targets with and without clusters irradiated on the PALS laser facility are analyzed preliminary, showing strong influence of target structure on process of laser light absorption. Heat and radiation transport in such targets are considered.