This article presents the results of a theoretical and experimental study of the convergent lensing effect in TEA-CO2 laser tubes with helical electrodes. The new characteristic is that all the excitation discharges are eccentric with respect to the axis of the tube. A model of the lensing effect, based on the theory of a gas lens, has been used to study the influence of the energy of excitation, the composition of the gas mixture, and the distance separating each discharge from the tube axis. An experimental study reveals the importance of these factors. [Journal translation