DYNAMIC PLASMA RESPONSE IN LASER-PHOTODETACHMENT EXPERIMENTS IN HYDROGEN PLASMAS

The theory of the dynamic plasma response in laser-photodetachment exp eriments in low pressure hydrogen plasmas is extended to include the e ffects of the self-consistent electric field. The H- rich plasma is mo deled via a hybrid fluid-kinetic approach in which the electrons and p ositive ions are described by the fluid theory, while the negative ion s are treated within the ballistic kinetic theory. Both slab and cylin drical geometries of the plasma region illuminated by the laser are an alyzed. The model is applied for studying the space-time evolution of various plasma species after the photodetaching laser pulse. The exper imentally observed overshoot in the time dependence of the electron de nsity perturbation on the axis or plane of symmetry was analyzed in de tail. The overshoot is due to the depletion of the positive ions as th e result of the self-consistent electric field. The magnitude of the o vershoot and the time of the maximum depletion of the positive ions ar e sensitive to the ratio between the electron and positive ion tempera tures.