Comparison of Langmuir Probe and rf Capacitance Probe Electron Density Measurements in Low‐Density Plasmas

摘要

Electron densities calculated from data obtained in the laboratory by dc and ac probes simultaneously exposed to low‐density low‐pressure air plasmas are compared. With electron densities between about 1011 and 1012 m-3 and collision frequencies on the order of 108 sec-1, data from a rf capacitance probe operating near 5 MHz and data from the ion saturation region of a dc probe each yield electron density values that generally agree within a factor of 2. By the use of a differential pressure cell, lower electron densities, ∼109 m-3, and reduced collision frequencies, ≪105 sec-1, were obtained. Under the latter conditions the dc probe operation was erratic but the ac probe operated satisfactorily, and operated as expected theoretically even under the laboratory limitations.