ELECTRON-ENERGY DYNAMICS IN A RF DISCHARGE WITH TRAPEZOIDAL DRIVING VOLTAGE - COMPARISON OF EXPERIMENT AND PARTICLE-IN-CELL MONTE-CARLO COLLISION SIMULATION

We report on the properties of a special RF discharge characterized by a trapezoidal shape of the driving voltage pulse. This driving mode o ffers an advantage in comparison to the common sinusoidal voltage-in a llowing the separation in time of effects which are connected with the time derivative of the driving voltage (displacement current, alpha-m echanism) from effects connected with the amplitude of the driving vol tage (production of electrons at the electrodes, gamma-mechanism). The energy gain and loss of electrons in this RF discharge are studied in a collision-dominated helium discharge with special emphasis on the a lpha-mechanism. Experimental results of space- and time-resolved plasm a-induced emission spectroscopy are compared and combined with the res ults of a particle-in-cell Monte Carlo collision simulation. it is dem onstrated that the electrons gain energy during the temporal change of the discharge voltage at high neutral particle pressure (400 Pa) in t he vicinity of both sheaths and that they dissipate energy in these re gions by inelastic collisions. At a lower neutral particle pressure (1 00 Pa) the electrons gain energy in the vicinity of the expanding shea th and lose energy at the contracting sheath. In this case the energy loss by inelastic collisions takes place in the bulk plasma.