期刊
PLASMA SOURCES SCIENCE & TECHNOLOGY
卷 26, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/1361-6595/aa56d7
关键词
electron sheath; presheath; particle-in-cell; laser collision-induced fluorescence
资金
- Office of Fusion Energy Science at the US Department of Energy [DE-AC04-94SL85000, DE-SC0001939]
- US. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scients, Office of Science Graduate Student Research Program (SCGSR)
- DOE [DE-AC05-06OR23100]
Electron sheaths form near the surface of objects biased more positive than the plasma potential, such as a Langmuir probe collecting electron saturation current. Generally, the formation of electron sheaths requires that the electron-collecting area be sufficiently smaller (root 2.3m(e)/M times) than the ion-collecting area. They are commonly thought to be local phenomena that collect the random thermal electron current, but do not otherwise perturb a plasma. Here, using experiments on an electrode embedded in a wall in a helium discharge, particle-in-cell simulations, and theory it is shown that under low temperature plasma conditions (T-e >> T-i) electron sheaths are far from local. Instead, a long presheath region (27 mm, approximately an electron's mean free path) 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. This fast flow is found to excite instabilities, causing strong fluctuations near the sheath edge.
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