Transverse inhomogeneity of the low-pressure discharge in a gas mixture

The transverse distribution of neutral and charged species in mixed gas plasma is calculated within a simplified model. The fluid equations for densities, velocities and self-consistent field are derived and solved numerically. The appearance of a dip in the centre of the heavy-species profile is found and interpreted. The depletion of ions near the centre occurs when the ionization length of the heavy impurity is less than the plasma dimension, while the length remains large for the main gas.