AUTHOR=Zhang Yunchao , Charles Christine , Boswell Roderick W. 

TITLE=Density Measurements in Low Pressure, Weakly Magnetized, RF Plasmas: Experimental Verification of the Sheath Expansion Effect

JOURNAL=Frontiers in Physics

VOLUME=5

YEAR=2017

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2017.00027

DOI=10.3389/fphy.2017.00027

ISSN=2296-424X

ABSTRACT=<p>This experimental study shows the validity of Sheridan's method in determining plasma density in low pressure, weakly magnetized, RF plasmas using ion saturation current data measured by a planar Langmuir probe. The ion density derived from Sheridan's method which takes into account the sheath expansion around the negatively biased probe tip, presents a good consistency with the electron density measured by a cylindrical RF-compensated Langmuir probe using the Druyvesteyn theory. The ion density obtained from the simplified method which neglects the sheath expansion effect, overestimates the true density magnitude, e.g., by a factor of 3 to 12 for the present experiment.</p>