Seeding of ambient electrons in critical velocity ionization

Summary form only given. Despite repeated demonstration of high ionization efficiencies in critical ionization velocity (CIV) experiments in the laboratory, much lower efficiencies have been reported in space CIV experiments. A survey of the CIV experiments in space reveals that higher ambient electron density appears to favor ionization. Some theoretical reasons relating to the density correlation are discussed. Because the natural ambient electron density in the ionosphere is limited, an experiment is proposed in which electrons are seeded artificially to form a high-electron-density region through which a neutral beam is injected with a velocity above its critical ionization velocity. The electron seeding mechanism proposed is the chemi-ionization reaction Sm+O→SmO⁺+e^-, the product ion SmO⁺ being stable against molecular dissociative recombination. It is estimated that an ambient electron density several orders of magnitude higher than the natural one in the ionosphere can be achieved. A neutral beam of Sm with a velocity U exceeding U_*≈2.7 km-s^-1, the critical ionization velocity for Sm, is injected across the ambient magnetic field in the region of high ambient electron density. The results of simulations performed to determine that the feasibility of the proposed CIV space experiment are encouraging