Multidimensional effects in low-pressure discharges

The transport in low-pressure discharges, such as the ones commonly used in many industrial applications, is governed by diffusion. Most of the insights on the behaviour of these plasmas is obtained through the use of one-dimensional models. Such a treatment forces equality of the ion and electron fluxes and leads to the well known ambipolar diffusion. However, in realistic systems with metal walls, flux balance has to be satisfied only globally but not locally. This leads to a peculiar behaviour, with regions where the ion flux to the walls exceeds the electron flux and vice versa. In this contribution, the effect is investigated experimentally for a large area rectangular discharge chamber, which provides a simple geometry. The plasma is generated by inductive coupling provided by the recently developed INCA configuration. An array of wall-mounted planar probes allows the measurement of the spatial profiles across one of the major walls. The spatial distributions of the electron and ion fluxes, as well as of the plasma potentials, the densities and the electron temperature are measured and analyzed. The results demonstrate the expected deviation from local equality of the fluxes.