Design and Analysis of an ExB Probe for Measuring Multicharge Species Distributions in Hall Thruster Plumes*

An ExB probe, also known as a Wien filter, has been designed and characterized using particle tracing simulations to measure the species distribution in Hall thrusters and other ion sources. Permanent magnets are used to apply a uniform magnetic field perpendicular to the ion velocity, and a uniform electric field from two electrodes. Ions pass through a collimator and enter this ExB region. Ions whose velocities are not equal to E/B are deflected, while the undeflected ions are deposited on a metal collector and detected with a picoammeter. Using COMSOL Multiphysics, the electric and magnetic fields are simulated, and ion trajectories are traced to obtain error estimates in the velocity measurement. These estimates are made for species of ions relevant to Electric Propulsion, as multiple-charged ions are known to decrease the operating efficiency of Hall thrusters [1]. From the probe trace, the multi-charge species distribution can be estimated [2]. The ExB probe will be set up and calibrated with a 3-cm gridded ion source of known velocity distribution. 

[1]: R. Hofer and A. Gallimore. 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, (2003).

[2]: R. Shastry, et al. Review of Scientific Instruments 80.6 (2009).