Pattern Formation in Low-Pressure Radio-Frequency Plasmas due to a Transport Instability.

Pattern formation, observed experimentally in a radio-frequency plasma in annular geometry, and characterized by azimuthal symmetry breaking of the plasma parameters, is reported. The azimuthal modulation increases with increasing pressure in the range 1-300 Pa. These experimental observations are accurately described by a fluid model in which the transport coefficients are computed from a 0D Boltzmann kinetic equation. A linear stability analysis shows that unstable modulations develop at low and intermediate pressures, following an instability mechanism due to an energy transport effect-the instability mechanism lies in the sign of off-diagonal terms for the electron particles and energy fluxes expressed as functions of gradients of the plasma density and the electron temperature. This model is an excellent candidate to explain the occurrence of striations in radio-frequency plasmas.