Diffusion of Precursor Ions and Electrons Upstream of a Stong Shock Wave Propagating down a Shock Tube

摘要

Photoionization upstream of strong shock waves produces ion-electron pairs. These charged particles diffuse to the walls of the shock tube where they recombine unless they are first overtaken by the advancing shock. Consideration is given to this diffusion problem, governed by the particle flux equations and Poisson's equation for the self-consistent electric field, in the limiting situation when a dimensionless photoionization rate (alpha) and dimensionless shock speed (v sub s) are large, and the ratio of ion to electron diffusion coefficients (delta) is small. The alpha and v sub s limits separate the region of production by photoionization from regions of electron diffusion from regions of ion diffusion. The subproblems in these regions of charged particle diffusion. The delta limit separates regions are formulated and explicit solutions are obtained when the electrostatic potential at the shock surface is small. The electric current density to the shock tube wall is calculated and the result inverted to express the photoionization rate as a function of current density. (Author)