The main effort of the ICF target fabrication group is support of the experiments performed on the ''ISKRA-4'' and ''ISKRA-5'' laser systems. The main types of targets used in these experiments are direct drive, inverted corona, and indirect drive. A direct drive target is a glass spherical container coated with a metal or polymeric film and filled with a D-T mixture and some diagnostic gas.(1,2) The inverted corona target is a spherical shell with holes for introducing laser radiation. The inside surface of the shell is coated with a compound containing heavy hydrogen isotopes.(3,4) The indirect drive target is assembled from a spherical shell with holes for introducing laser radiation and a direct drive target placed in the shell center. The inside surface of the shell is coated with high-Z material(5) (Fig. 1).For production of direct drive targets, manufacturing techniques have been developed for both hollow glass and polystyrene microspheres. Hollow glass microspheres are fabricated by free-fall of liquid glass drops or dry gel in a 4 meter vertical kiln.(6) These methods allow us to manufacture glass microspheres with diameters from 50 mu m to 1 mm, wall thicknesses from 0.5 to 10 mu m, and aspect ratios (radius/wall) from 20 to 500. The microspheres have a thickness inhomogeneity less than 5% and non-sphericity less than 1%. Polystyrene microspheres are fabricated from polystyrene particles with a blowing agent in a similar vertical kiln. Polystyrene microspheres are fabricated with diameter up to 800 mu m and wall thicknesses from 1 to 10 mu m.

Fuel-containing layers in targets used in laser fusion experiments at the Iskra-4 and Iskra-5 facilities, have been investigated. The layers are formed from the condensed deuterium or deuterium-tritium mixture, as well as of metal hydrides and polyethylene containing deuterium and tritium.

Methods for control of the shell diameter, wall thickness and wall nonuniformity and also methods for selection of shells in fluid have been developed and investigated. The methods allow us to separate shells according to the diameter with 0.25 μ;m accuracy, to the wall nonuniformity with 5–7% accuracy, to make measurements of the diameter with 0.35 μ;m accuracy and wall thickness with 3–10%. These methods allowed us to develop the automated process cycle of control and selection of shells for laser fusion targets. A model automated line has been developed and joint operation of units has been investigated. The calculated automated line throughput during the shell analysis is 50–300 shells per hour, the control and selection accuracy for the diameter, thickness, and wall nonuniformity is 1%, 3–10% and 1–3%, respectively. Thus the foundations have been laid for an automated, high-quality target production technology for power stations based on laser fusion.

In selection of shells for laser fusion targets, measurement of the wall nonuniformity with an accuracy better then 100 Å is needed. With this aim, the possibility of using multiplebeam interferometry for shell inspection has been investigated. Technical approaches have been found which have made possible the advantages of multiple-beam interferometry. For one of methods, bases on the multiple-beam interference used to process oscillograms, the sensitivity of 20 Å has been obtained in the wall nonuniformity measurements.

An investigation was made of fuel films in targets used in experiments on laser thermonuclear fusion in Iskra-4 and Iskra-5 systems. These films were formed from condensed deuterium and a deuterium—tritium mixture, and also from metal hydrides and polyethylene containing deuterium and tritium.

A study was made of the use of multibeam interferometry methods in monitoring the parameters of laser fusion targets and their capabilities were estimated. Elimination of the influence of diffraction made it possible to reduce the error in the determination of the fringe shift by oscillographic recording to ΔN = ±1/300 of a fringe. This error made it possible to detect variations of the wall thickness of a shell target (microbubble) to within Δd = ±2nm, which in the case of a wall of thickness d∼1μ corresponded to Δd/d = ±0.2%. In measurements of the gas pressure in a shell target the error in the determination of the fringe shift amounting to 1/300 of a fringe gave rise to a gas pressure error of Δp = ±0.1 atm for shells ∼ 150 μ in diameter.

A nondestructive interferometric method was used to determine the gas pressure in laser fusion targets. The method was tested experimentally and the results were compared with those obtained by mass-spectrometric and ionization methods. The target lifetime was measured. The error in the interferometric determination of the gas pressure in shell targets ∼140 μ in diameter was ± 3 atm.