Ionization-drift turbulence in rf magnetron plasmas

Abstract

Electron density fluctuations in a rf hollow magnetron system are investigated. The weakly ionized and axially magnetized (B∼80 G) discharge supports nonlinear ionization-drift waves in the presence of the nonuniform rf-induced dc electric field and density gradient along the normal of the hollow electrode surface. The fluctuations have good coherence along B and are turbulent in the transverse plane. The turbulence is inhomogeneous along the density gradient. The power spectrum shows two major bands. The amplitude of the high-frequency oscillation is modulated by the low-frequency oscillation. In the transverse plane, the phase velocity is about the same as the diamagnetic drift velocity. It has one component along the diamagnetic drift direction and the other toward the electrode surface. The turbulence also induces anomalous cross-field electron current which deteriorates the electron confinement in the low-pressure regime. Generally, the system combines the nature of the reaction diffusion and the drift systems. The ionization process, the nonlinear transverse drifts under the nonlinear background, and the nonlinear wave-wave interactions drive the system to turbulence. The parametric dependence of the turbulence is studied and discussed in the paper.