Does presheath ion flow affect electron density measurements for Langmuir probes near boundaries?

It has recently been shown that Langmuir probes (LPs) measure an unphysically positive plasma potential in the presheath of low temperature plasma, near conducting boundaries at which ion rich sheaths form [Li et al., Plasma Sources Sci. Technol. 29 (2020) 025015]. It has been argued heuristically that the difference between plasma potential profiles measured by LPs and emissive probes (EPs), in the presheath, is related to ion flow caused by sheath formation. We present experimental evidence that the electron density is also overestimated by standard analysis in the presheath, that the two anomalies are interrelated, having to do with ion flow near the boundary where an ion rich sheath forms. We attempt to estimate the sheath expansion due to ion flow using the constraint of quasineutrality in the presheath. These experiments are performed in weakly collisional (λ_{mean-free-path}>>λ_D), low pressure (P_neutral ≤ 1 mTorr), low temperature (kT_e of order 1 eV), single ion species plasma, where the feedstock gas is Ar or He or Xe or Kr.