Distinguishing Between Thermalizing and Electrodynamic Coupling For Laser-compressed Thermonuclear Reactions

Abstract

In the gas-dynamic laser compression of plasmas for exothermal nuclear reactions, certain laser intensities must not be exceeded in order to reach sufficient thermalizing coupling. A criterion for this limitation is developed here, which shows that the published cases of Nuckolls (1974) and Brueckner (1974) are close to this threshold and may not need serious changes due to the coupling process. As weII as the long pulse scheme of Afanasyev et al. (1975), an alternative method exists in which very short and very high intensity laser pulses are applied, thereby avoiding thermalization but generating fast imploding cold and thick plasma shells due to nonlinear ponderomotive forces of optical explosion. A necessary and sufficient condition for this electrodynamic coupling is derived, and the general nonlinear force equation is integrated to derive ion energies and their exact linear increase with ion charge. Experiments indicating the predominance of the nonlinear force are then analysed. The derived criteria are used to explain examples of nonlinear force compression giving 1000 times greater efficiencies for nuclear reactions than the gas-dynamic case.