Single Langmuir probe dignostics for characteristic parameters of the beam plasma in xe ion thruster

Successful integration of ion thrusters into spacecrafts requires comprehensive evaluation of the possible plume-spacecraft interactions between them. In order to provide experimental proofs for the integration, after designing and developing a single Langmuir probe system, we measured and analyzed the special distribution of beam plasma characteristics of a xenon ion thruster using the system. The Kaufman type ion thruster used in this experiment has twin grids that are convex outward. In the experiment, the background pressure was maintained at 3 mPa. Different from conventional quiescent plasmas, the ions in the beam had a very large directed velocity and would greatly increase the probe current. Hence, the standard interpretation of I-V curves should be reconsidered and revised. In order to minimize the directed current in the ion saturation current, the Langmuir probe used in the test was set parallel to the centerline of the ion thruster. Experimental results show that the trends of the floating potential, plasma potential, and ion density are similar: these values at different radial locations decrease with increasing axial distances. However, it is noticed that there are extremely low values in the profiles of floating potential, plasma potential, and ion density, because these points are not in the beam region. According to the axial and radial locations of these points, the beam divergence(16.014°), grid radius(within 71.3~111.3 mm), and beam configuration of the thruster can be estimated.