Kinetic picture of ion acoustic wave reflection using laser-induced fluorescence

Plasmas are fluids very similar to gases, except some fraction of the molecules is ionized (meaning they have one more/fewer electron on them). In addition, there are free electrons and neutral particles. Plasmas behave in many ways similarly to gases, but the existence of those free charges changes the behavior of the fluid completely. An example of this is the pressure wave we call sound. In plasmas these waves are not just mechanical, they are electromechanical. Ion-acoustic waves (IAW) are different than sound waves in gases. In gases, the wave compression is communicated by nearest neighbor interactions (collisions). In plasmas, the wave depends on "mean fields" which act in the absence of particle collisions. For the specific case of the interaction of ion-acoustic wave with a boundary, the existence of DC electric fields can have important effects through the particle orbits - the absorption or reflection of the wave can depend on boundary fields more than on the material wall. In this thesis I present the first observation of ion-acoustic wave reflection using laser-induced fluorescence (LIF). LIF is a technique where the laser light excites some of the ions in the plasma, making them emit light at a different wavelength/color (therefore "fluoresce"). This method allows to make measurements of the ions without a affecting their motion (unlike probes). We can also investigate how the ions with different velocities react distinctly to the wave and its reflection. With the help of LIF, the aim of this dissertation is to reveal new information regarding the behavior of ion-acoustic waves and to try and fill some of the gaps that exist in the understanding of IAW incident on a plasma boundary.