Far-Field RF Sheaths due to Shear Alfv\'{e}n Waves in the LAPD

Ion cyclotron resonance heating (ICRH) is an important tool in current fusion experiments and will be an essential heating component in ITER. ICRH could be limited by deleterious effects due to the formation of radio frequency (RF) sheaths in the near-field (at the antenna) and in the far-field (e.g. in the divertor region). Far-field sheaths are thought to be caused by the direct launch of or mode conversion to a shear Alfv\'{e}n wave with an electric field component parallel to the background magnetic field at the wall.\footnote{D. A. D'Ippolito and J. R. Myra, \emph{Phys. Plasmas} \textbf{19}, 034504 (2012).} In this experiment a limiter plate was inserted into a cylindrical plasma in the LAPD (n$_{e}$ $\sim$ 10$^{10-11}$ cm$^{-3}$, T$_{e}$ $\sim$ 5 eV, B$_{0}$ = 1.2 kG) and RF sheaths were created by directly launching the shear Alfven wave. Plasma potential measurements were made with an emissive probe. DC plasma potential rectification was observed along field lines connected to the plate, serving as an indirect measure of RF sheath formation. 2-D maps of plasma properties and rectified plasma potential will be presented. This research is part of an ongoing campaign to study the formation and structure of RF sheaths.