Ion acoustic wave characterization in a moving plasma to find bulk flow velocity

Summary form only given. The bulk flow velocity can be found directly through interpretation of the propagating characteristics of an ion acoustic wave. When the bulk flow velocity is greater than the ion acoustic velocity, as it is in many plasmas, the ion acoustic wave propagation zone is limited to a cone emanating from the ion acoustic wave source which is directed downstream of the plasma flow. The propagation region of the ion acoustic wave is dependent on the ratio of the flow velocity to the wave velocity. The ion acoustic wave velocity can be determined by analyzing the dispersion relation of the wave. Hence the bulk flow velocity is found by characterizing both the propagation zone and the ion acoustic wave dispersion relation. This method of measuring flow velocity relies only on knowledge of the propagation of ion acoustic waves in a plasma, and not on a model of the probe-plasma interaction. A simple electrostatic probe is used where the probe diameter is much smaller than a Debye length. We present flow velocity results of a stationary plasma thruster using this technique and compare them with measurements using an RPA.