Particle-in-cell simulation of grid sheath oscillations in a double-plasma device

The oscillation process around a strongly negative grid in a double-plasma device is studied with one-dimensional particle-in-cell simulation. The code is an extension of PDP1, and its proper adaption to the present situation is described. For asymmetric operation of the double-plasma device, the formation of “virtual anode oscillations” (VAOs) is observed. The scaling law f∝n^1/2 U_g^-α, which formerly was derived from the transit time through a static Child-Langmuir sheath, is now recovered with α=0.33 by self-consistent simulations. A group of ions, that is trapped in the sheath, leads to feedback stabilization of the VAO. The simulations show that ion bunches that have gained energy in the VAO process are periodically injected into the source plasma where they excite damped ion waves