The energy model of a pulse nuclear reactor pumped laser system - nuclear pumped optical quantum amplifier (NPA) was designed at the IPPE for experimental demonstration of unique features of Nuclear Pumped Lasers.     The NPA consists of ignition reactor and laser module (see Fig. - 27 kb). A twin-core fast burst BARS-6 reactor is used as ignition module. The laser module (LM) is a cylindrical structure sized to provide the space required for housing the two cores of reactor module and the other components of the system. The diameter of laser module is 1700 mm, and the length is 2500 mm. The LM consists of the laser active elements (LAEL’s), LAEL imitators and neutron moderator elements. The laser module is surrounded by the two rows of neutron reflector elements. The laser module is a subcritical booster with effective multiplication factor less than 1.     The LAEL assembly consists of a thin-wall stainless steel tube 50 mm in outer diameter and 2500 mm in length and whose internal surface is coated with ~ 5 µm thick uranium-235 metal and includes optical windows filled with a laser active medium. Ar-Xe mixture (200:1), at approximately normal pressure, is used as a laser active medium and has been chosen for this application because it is the medium mostly used in studies performed at the present time.     The imitator is a neutron-physical copy of the LAEL. It consists of two thin-wall aluminum tubes concentrically arranged to provide an annulus which is filled with uranium-235 dioxide. The mass of uranium-235 in the imitator is equal to the mass of the uranium coating LAEL’s. The use of imitators in laser module is extremely important because this provides a method for varying the energy of the model by simply replacing any required number of imitators with LAEL’s.     The internal reflector consists of a thin-wall stainless tube with paraffin. If required, the NPA could be provided with an internal neutron reflector of up to 7 cm thick.     The NPA functions as follows. Neutrons from the ignition reactor passing through the LM are moderated and induce a chain fission reaction of uranium-235 in the coating of LAEL. The fission fragments captured in Ar-Xe mixture induce plasmas so that the inversion population of Xe1 levels corresponds to the laser transition with wavelength 1.73 micron. The energy stored in the inversion population is extracted from laser module by the optical system of the model. The "master oscillator - two round trip amplifier" optical scheme (see Fig. - 6 kb) is applied. Electron laser is used as a master oscillator.     In the case where all of the imitators are replaced with LAEL’s (650 units) the energy of the model laser pulse can reach 50 kJ for the pumping pulse duration ~ 10 ms.     First criticality program for this system is succesfully completed. At present, the energy start up procedure is in progress. At the first step, seven LAELs were used in laser module for laser measurements.
	The basic parameters of OKUYAN system Parameter Value  Number of fissions in BARS-6 reactor  5.1017  Pulse duration in the laser module  1-10 ms  Lasing medium  Ar-Xe  Laser transition  Xe1  Laser beam wavelength  1.73 µm  Laser beam energy (650 LAELs)  up to 50 kJ
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