Exact solution for the generalized Bohm criterion in a two-ion-species plasma.
For a weakly collisional two-ion species plasma, it is shown that the minimum phase velocity of ion acoustic waves (IAWs) at the sheath-presheath boundary is equal to twice the phase velocity in the bulk plasma. This condition provides a theoretical basis for the experimental results that each ion species leaves the plasma with a drift velocity equal to the IAW phase velocity in the bulk plasma [D. Lee et al., Appl. Phys. Lett. 91, 041505 (2007)10.1063/1.2760149]. It is shown that this result is a consequence of the generalized Bohm criterion and fluid expressions for the IAW phase velocities.
Lee
Dongsoo
D
Department of Engineering Physics, University of Wisconsin at Madison, Madison, Wisconsin 53706, USA.
Oksuz
Lutfi
L
Hershkowitz
Noah
N