An asymmetric capacitively coupled radio frequency discharge was investigated. The planar RF electrode was made of stainless steel and had a diameter of 120 mm. It was powered at 13.56 MHz by an RF generator (Advanced Energy, Cesar 133) and an automatic matching network (Advanced Energy, Navio). The RF electrode was positioned at a distance of 55 mm beneath the top surface of the grounded reactor vessel, which consisted of aluminum and was cylindrically shaped, with a diameter of 240 mm and a height of 105 mm. The applied RF power was varied between 20 and 100 W.