ABSTRACT
A one-dimensional kinetic theory of sheaths surrounding planar, electron-emitting surfaces is presented which accounts for plasma electrons lost to the surface and the temperature of the emitted electrons. It is shown that ratio of plasma electron temperature to emitted electron temperature significantly affects the sheath potential when the plasma electron temperature is within an order of magnitude of the emitted electron temperature. The sheath potential goes to zero as the plasma electron temperature equals the emitted electron temperature, which can occur in the afterglow of an rf plasma and some low-temperature plasma sources. These results were validated by particle in cell simulations. The theory was tested by making measurements of the sheath surrounding a thermionically emitting cathode in the afterglow of an rf plasma. The measured sheath potential shrunk to zero as the plasma electron temperature cooled to the emitted electron temperature, as predicted by the theory.
ABSTRACT
A one-dimensional model is used to describe the evolution of charged particles in a plasma sheath driven by an asymmetrically pulsed dc bias in the frequency range of 100 kHz to 10 MHz. The temporal-spatial evolution of the sheath is obtained through the simultaneous solution of Poisson's equations, the ionic fluid equations and a Boltzmann treatment of the electrons. Calculations are performed to demonstrate the effects ionic inertia and sheath restructuring have on the temporal dependence of current and energy of the ions arriving at the driven electrode. The temporal scale is observed to depend on the bulk density of the plasma. The pulse frequency, the pulse duty, and the capacitive coupling of the pulse to the driving electrode are varied to demonstrate the influence of these factors on the energy distribution of the ions extracted from the plasma to the electrode.
