Ion soliton observation with laser-induced fluorescence

A laser-induced fluorescence observation of ion-acoustic waves in a collisionless unmagnetized double plasma multipolar device is presented. The optical pumping effect is found to be critical for the interpretation of fast changes of the ion velocity distribution functions induced by the propagation of a soliton. To take this effect into account, the continuity equation is used. The laser-induced fluorescence diagnostic shows that the separation of solitons requires a small plasma drift in the backward direction (reverse direction of the soliton propagation) and that the precursor ions are in fact a precursor wave.