A computational- simulation study was performed to assess the feasibility of laser-induced fusion of deuterium nuclei with tritium nuclei as a means of generating neutrons for use in neutron radiography. [D-T fusion reactions produce α particles (He nuclei) plus the desired neutrons.] As in prior studies of laser-induced D-T fusion, the basic idea is to irradiate a small deuterium-and- tritium-containing target with a brief, intense laser pulse that causes a shock wave to propagate into the target. The shock wave ionizes and accelerates a substantial portion of the D and/or T molecules, resulting in, among other phenomena, collisions between D and T nuclei. The question of feasibility is essentially the question of whether, by use of a realistic target and a realistic laser pulse, a sufficient number of ions could be accelerated to sufficient kinetic energy such that the number of resulting D-T fusion reactions would suffice to produce a radiographically usefully large number of neutrons.
Shortly before the beginning of the study reported here, the program was enhanced by incorporation of a variety of models. One of them is a kinetic impact-ionization model that is a hybrid between a classical particle in cell model and a direct simulation Monte Carlo model. In this hybrid model, particles are represented as being pushed in their self-consistent electromagnetic field. At every time step, particles within a cell are considered for possible collision (and therefore reaction) by use of Monte Carlo methods. The main parameters required in this model are energy-dependent cross sections for ionization. While the model was designed mainly for ionization processes, it can relatively easily be adapted to other reaction-type processes, including fusion: in this study, the adaptation to D-T fusion was effected by incorporating a parameterized submodel of the energy dependence of the cross section for a D-T fusion reaction.
This work was done by Jean Luc Cambier of the Air Force Research Laboratory, and Peter Messmer, Kevin Paul, and Peter Stoltz of Tech-X Corp.
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Kinetic Modeling of Laser-Induced D-T Fusion
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This article first appeared in the June, 2008 issue of Defense Tech Briefs Magazine.
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