Physics of Nuclear Induced Plasmasand Nuclear Pumped Lasers

Investigations in the field of physics of nuclear-induced plasmas and nuclear pumped lasers (NPL) were started in the IPPE in 1981. They are aimed at the development of laser systems with pumping from pulse nuclear reactors. At the reactor power pulse, neutrons penetrate into the laser-active medium containing U-235 of heterogeneous or homogeneous form and induce its fission. As a result of fission fragments stopping in the medium a nuclear-induced plasma generates there with the parameters required for the laser to operate.

The promising aspects of these systems are determined by the unique properties of a pumping source: high capacity, and the possibility of pumping considerable volumes of laser-active media due to a high penetrability of neutrons. These properties enable us to hope for creating superpower laser units of long-term operation which could find a wide application in power engineering, technology, and space communication.

Experimental, calculational, and theoretical investigations performed in the IPPE in this field study nuclear-induced plasma kinetics, search for effective laser media, develop and substantiate concepts of reactor pumped laser systems, and create a demonstrational specimen of a laser system with pumping from a pulse reactor.

In order to study plasma kinetics up-to-date methods of experimental physics are used: nanosecond time-of-flight technique, method of delayed coincidencies in the nanosecond and microsecond range, single-photon spectroscopy, etc.

The experimental basis comprises various sources of nuclear reaction products, nuclear particles, photon and electron detectors, monochromators for ultra-violet, visible and infra-red ranges, high-vacuum and gas equipment, and modern electronic equipment. In the course of investigations, some very important data was obtained. They concern such processes and characteristics of nuclear-excited plasma as primary ionization of various media by fission fragments, electron distribution function in the condensed media, elementary processes of excitation and relaxation of plasma components, and a track structure of the nuclear-induced plasma.

Along with the development of kinetic models and calculational and theoretical investigations of generation parameters of various media, the methods of subthreshold medium diagnostics with the help of californium-252 spontaneous fission fragments were developed and widely applied. These methods make it possible to judge the potential of application of the material under study as an active medium for a nuclear pumped laser before conducting complicated and expensive experiments using pulse reactors.

A concept of a laser system with pumping from a pulse reactor was formulated in 1987 in the IPPE. This system was called an optical quantum nuclear pumped amplifier (OKUYAN). Consideration was given to making use of the system like this in the laser thermo-nuclear fusion units. The advanced features of application of this system was shown in the course of solving the problem of laser fusion. By now certain work has been done on its analytical and experimental validation. The research comprises development of techniques, codes and calculations of transient neutronic parameters, kinetics, dynamics, laser and thermo-physical parameters of the OKUYAN as well as simulation of neutron kinetics of the related reactor system using critical assembly.

Based on the experience gained, a creation of an OKUYAN demonstrational facility was started in 1990. The facility includes a reactor unit based on the two-core pulse fast reactor of the burst type ("BARS-6") and a laser unit consisting of laser-active elements (LAEL), and elements of neutron moderator and reflector. The mixture of noble gases is considered as a first version of the active medium. The wave length of laser transition is 1.73 micron. In the course of the facility construction in the Institute, technological development of its elements is being performed (uranium LAEL coating, optical windows, elements of optics and master oscillator) and pilot laser and reactor units and systems are being fabricated.

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