It is known [1, 2] that fast heating of materials by pulsed flows of penetrating radiation gives rise to compressive stresses whose amplitude in the solid-phase region is proportional to the concentration of the absorbed energy.The time lag of the absorbing medium causes a motion in the form of compression waves (or shock waves) and expansion waves. The interaction of two counter waves of the latter type gives rise to tensile stresses in the material with duration rt "-" A/c (A is the thickness of the heated layer and c is the speed of sound). The amplitude of these stresses depends, in the general case, on the absorbed energy, the heating rate (the rate of energy supply), the distribution of the absorbed energy in mass, and the physicomechanical properties of the medium. The appearance of tensile stresses produces conditions for the development of failure. When critical amplitude-time characteristics of the impulse of tensile stresses are reached in a cross section of the sample, failure of the normal separation (spalling) type occurs in it.Investigation of the dynamic effects caused by fast heating of a material is very important for applications, because the capabilities of modern high-energy pulsed facilities are largely determined by the mechanical strength of elements, units, and constructions.The thermal-shock method used in studies of failure allows a considerable extension of the range of the material states studied as compared with conventional methods (shock-wave and explosion loadings [3, 4]). Thus, the results of these investigations provide new information on the behavior of specific materials and are of independent importance for the physics of failure, in particular, in developing models of failure under high-speed deformation that fit the process well.Materials Can be fast heated by impulsive penetrating radiation (in particular, by a nuclear explosion [5]) and by pulsed beams of charged particles [3,[6][7][8][9][10]. The spalling of some solid media (colored ice and polyvinyl chloride plastic) under absorption of the laser-radiation energy is considered in [1, 8, 10]. The spalling of some metals upon fast space heating by high-current electron beams is described in [3, 5,[7][8][9] 10].Sources of impulsive radiation allow one to investigate the behavior of materials in the region of extreme loading parameters and over a wide range of initial temperatures.In studies of the failure of metals under laboratory conditions, high-current accelerators of relativistic electrons are the most widely used sources of pulsed pressure. Use of these accelerators offers unique possibilities and new avenues of attack on the problem of failure of solid bodies in the submicrosecond range of durability for the following acting parameters: rate of energy supply dE~dr of up to 10 al J/(g 9 sec), concentration of the absorbed energy E ~ 1-103 J/g, initial temperatures To = 4K-0.8Tmelt, and electron energy Ee "~ 1-10 MeV. The experimental methods developed to date in combination with mathematical modeling make it possib...
Results of experimental and calculation and theoretical investigations on eximer laser pumping by y-radiation powerful source is presented. Based on the results of investigations there are proposed laser systems for study of thermonuclear targets compression physics.In our earlier reports [1 ,2] we informed about use basic possibility for researches of inertial thermonuclear fusion and plasma physics research of high powerful gas lasers,pumped by y-radiation of a small (less than 1 kiloton)nuclear explosion. As a pumping source the nuclear explosion possesses a number of unique peculiarities essential for laser thermonuclear fusion problem. This is its small dimensions defining the pumping high space and time symmetry; high of rradiation density providing the pumping high specific power ( I 0-1 00 Me i7cm'); this is the pumping high specific power of laser gas medium (0.3-1 .5)J/cm. as well as high degree of pumping uniformity at E,> 1 MeV. These peculiarities are easily realized using the longitudinal laser pumping in onepuss "running wave" mode with synchronous propagation along active volume of medium excitation area by ?.radiation and laser pulse generation front. The medium excitation mechanism, at that, is consisted of y..radiation Comptonscattering and energy transmission to secondary electrons in recombination-nonequilibrium plasma. 252 SPIE Vol. 3268 • 0277-786X/98/$1O.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspxGamma-pumped lasers have the advantagesaheir laser radiation pulses one can use without any conversion of their time and spectral characteristics. Duration and time structure of laser pulse at the use wrunning wave" mode with the longitudinal pumping is definitely determinate by fly-pulse, and if y-pulse duration rather small, it is necessary to form laser pulse with use of nonlinear optics elements, in addition. The possibility of direct pumping of short-wave eximer lasers exclude of the initial laser radiation spectral conversion and there occurs the possibility to produce systems with the laser radiation wavelength of large range. We shall explain these possibilities in detail lower.Experimental and calculation-theoretical researches performed YNIIEF were justified and formed the basis of our later proposals. Much attention is given to eximer and radiation-chemical lasers, in optimal way corresponding optimally the condition of the pumping by short y-pulse in the "running wave" mode. This is eximer UI/-laser on XeF* molecule (2. 0.35 1 irn) and radiationchemical IR-laser on XeF* molecule (? 3 urn) [3-6].Operation mixtures composition optimization and estimation of their spectral radiation characteristics have performed in laboratory investigations with excitation the small of active media by electrons of high current electron accelerators. Simultaneously with these investigations there were made calculation and theoretical estimations of the expected characteristics of eximer UV-lasers with y-ray pu...
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