presheath

plural presheaths

1. A region in advance of a sheath

   Instead, a long presheath region extends into the plasma where electrons are accelerated via a pressure gradient to a flow speed exceeding the electron thermal speed at the sheath edge.

   2015, Benjamin T. Yee, Brett Scheiner, Scott D. Baalrud, Edward V. Barnat, Matthew M. Hopkins, “Electron Sheaths: The Outsized Influence of Positive Boundaries on Plasmas”, in arXiv