Accurate measurement of the ion saturation current collected by a cylindrical Langmuir probe in cold plasmas. Issue 11 (16th June 2020)

• Record Type: Journal Article
• Authors: Díaz‐Cabrera, Juan Manuel; Fernández Palop, José I.; Regodón, Guillermo F.; Ballesteros, Jerónimo
• Is Part Of: Plasma processes and polymers. Volume 17:Issue 11(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-06-16
• Subjects: cold plasma -- DC discharges -- Langmuir electrostatic probe -- noble gases -- surfaces; Plasma polymerization -- Periodicals; Plasma-enhanced chemical vapor deposition -- Periodicals; Plasma chemistry -- Periodicals
• DOI: 10.1002/ppap.202000073
• Languages: English
• ISSNs: 1612-8850

Abstract

Abstract: This paper analyzes the results of accurate measurements of the ion current collected by a cylindrical Langmuir probe immersed in cold argon, neon, and helium plasmas. These measurements make it possible to study the influence of the positive ion‐to‐electron temperature ratio β = T + / T e on the collected ion current, providing valuable information about the trajectory described by the positive ions when falling toward the probe. Several criteria have been applied to discriminate whether the ion current is described by using the orbital motion limited theory or the radial motion theory. In all the studied argon and neon plasma discharge conditions, the criteria indicate that the positive ion current collected by the probe is appropriately described by the radial motion theory; however, as β increases, some criteria indicate a trend toward the orbital theory. In contrast, for the studied helium plasmas discharge conditions, a transition from radial to orbital motion has been measured. Abstract : This paper analyzes how positive ions fall toward a cylindrical surface immersed in a plasma as a function of the positive ion thermal motion. Their results are important not only in Langmuir probe plasma diagnosis but also in material technological processes involving plasma wall/surface interactions. The article presents the experimental results obtained in the application of several criteria to discriminate whether the positive ion current collected by a cylindrical Langmuir probe is described by the orbital or radial theories in low‐pressure, low‐temperature argon, neon, and helium plasmas as a function of the ratio between positive and electron temperature, β .