Momentum Transfer Interaction of a Laser-Produced Plasma with a Low-Pressure Background

The expansion of a laser-produced metallic plasma into a photoionized hydrogen background has been experimentally studied. Langmuir probe and microwave diagnostics have detected an interaction front which decelerates with a dependence on background density and time consistent with a momentum coupling between the laser plasma and the ionized fraction of the background. An ion precursor has also been observed. Calculations of scattering cross sections indicate that multiple-encounter Coulomb scattering will dominate collisional momentum transfer. The leading edge of the laser plasma contains multiply charged ions of charge state z≥5, and collisional effects appear adequate to explain the principal features of the momentum coupling. The ion precursor may have a collisionless origin.