Effect of Ion - Neutral Collisions on Sheath Potential Profile IEPC - 2013 - 346

To investigate the effect of ion-neutral collisions on plasma sheaths over floating surfaces, experimental measurements of near-wall plasma potential profiles are conducted in a multidipole plasma device with neutral pressures of 1 and 5 mTorr-Ar. Sheath and presheath potential profiles are measured over a HP grade boron nitride sample using an emissive probe, employing the technique of inflection points extrapolated to zero emission. Measured sheath thicknesses range from 1.2 to 1.9 cm while experimental ionneutral mean free paths range from 1.2 to 6.0 cm, allowing both presheath and sheath length scales to be resolved. The plasma device generates electron number densities 1.3 x 10 and 1.9 x 10 cm. The electron energy distribution function is bi-Maxwellian with distinct hot (3.4 – 8.4 eV) and cool (0.7 – 0.8 eV) electron populations as measured by a planar Langmuir probe. Experimentally measured potential profiles display qualitative agreement with the theoretical results of a fluid asymptotic matching solution for the sheath and presheath potential profile. 1 Graduate Research Assistant, School of Aerospace Engineering, [email protected] 2 Associate Professor, School of Aerospace Engineering, [email protected] 3 Graduate Research Assistant, School of Engineering and Applied Science, [email protected] 4 Associate Professor, School of Engineering and Applied Science, [email protected] 5 Particle-in-cell Consulting Inc, Washington DC, [email protected]