Striations in a low pressure RF-driven argon plasma

In experiments we observed spatially periodic modulations of the light emitted by an argon plasma in a tube of 30 cm length and 2.5 cm radius. The plasma is capacitively excited by RF electrodes positioned towards the ends of the tube. The argon pressure is approximately 2 Torr. We studied the space and phase dependence of the light emitted by the spheroidally shaped striations. Temporal phase-shifts within one striation were clearly visible. Furthermore, a simple model of the electric field modulation inside the tube was used in conjunction with a Monte Carlo model in order to study the electron kinetics in the tube. The excitation rates resulting from this model are compared with the measurements.