title: On the reliability of scrape-off layer ion temperature measurements by retarding field analyzers.
abstract: The retarding field analyzer (RFA) is one of the only widely accepted diagnostics for measurements of ion temperature Ti in the tokamak scrape-off layer. In this paper we analyze some instrumental effects of the RFA and their influence on Ti measurements. It is shown that selective ion transmission through the RFA slit is responsible for an overestimation of Ti by less than 14%, even for a relatively thick slit plate. Therefore, thicker slit plates are preferable, since they reduce, e.g., the risk of melting during off-normal events, and the effect of positive space charge inside the cavity. The influence of the electron repelling grid, as well as misalignment of the slit with respect to the magnetic field on Ti measurements are negligible.
authors.affiliation: CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. martin.kocan@cea.fr
authors.forename: M
authors.initials: M
authors.lastname: Kocan
authors.forename: J P
authors.initials: JP
authors.lastname: Gunn
authors.forename: M
authors.initials: M
authors.lastname: Komm
authors.forename: J-Y
authors.initials: JY
authors.lastname: Pascal
authors.forename: E
authors.initials: E
authors.lastname: Gauthier
authors.forename: G
authors.initials: G
authors.lastname: Bonhomme