Development of the dual-collector ExB probe

In an ExB probe, the drift tube length can control the balance between the signal-to-noise (SN) ratio and the ion velocity distribution function (IVDF) measurement resolution. The longer drift tube filters more ions out and provides a more accurate IVDF, but the SN ratio is lower. In the dual-collector ExB probe, which is developed at the University of Illinois Urbana-Champaign (UIUC), the drift tube is split into two semi-cylindrical tubes. The two semi-cylindrical tubes have different lengths, and each tube has an identical collector on its end. This dual-collector drift tube enables two different measurements in the distinct modes, (one lower SN ratio but higher resolution, the other higher SN ratio but lower resolution) at the same time. The dual collector ExB probe was tested with the 10 cm electron cyclotron resonance gridded ion thruster opearting with 1 sccm nitrogen (N2) and argon (Ar). In the N2 case, the long ExB probe detected more peaks than the short ExB probe did, and the difference in the IVDF measurement accuracy was highlighted. In the Ar case, the short ExB probe detected smaller peaks that were buried in the noise in the data from the long ExB probe, and the difference in the SN ratio was highlighted. The true IVDF was reconstructed from the long ExB probe data using the analaytically-obtained [1, 2] Transmittancy matrix. However, it was unsuccessful to validate it by comparing the measured short ExB probe data and the expected short ExB probe data from the analytically-obtained Transmittancy matrix and the reconstructed IVDF.