Effect of reaction products kinetic on stability of thermonuclear spark ignition

Abstract

Thermonuclear spark instability driven by reaction products momentum transfer is considered in this paper. General theory of such instability was developed by Lykov [1] based on one-group particles transport equation solving. Main dimensionless parameter of this problem is l/λ, where λ is the perturbation wavelength and l is the reaction product mean free path. In two limiting cases of l/λ ratio we recalculated perturbations growth rates in a more precise manner, obtaining reaction products distribution function through Fokker-Planck equation. While our results are generally consistent with those of Lykov's work, instability growth rates predicted in this investigation are somewhat smaller than the previously reported values. By performing a sequence of hybrid kinetic-fluid simulations in code FRONT3D, we demonstrate their better agreement with our asymptotic predictions. However, it was shown that in a wide range of l/λ ratio the instability growth rates are well described by Lykov's theory. We apply Champan-Enskog method to describe plasma ions deviations away from Maxwellian distributions, which appears from interaction with higly non-maxwellian reaction products. We derive an equation, that connects concentration of non-equilibrium particles with such parameters as ion momentum relaxation time and reaction rate. As it was shown, for typical ICF parameters, non-equilibrium part does not exceed several percents even at the burn peak.