title: Increased upstream ionization due to formation of a double layer.
abstract: We report observations that confirm a theoretical prediction that formation of a current-free double layer in a plasma expanding into a chamber of larger diameter is accompanied by an increase in ionization upstream of the double layer. The theoretical model argues that the increased ionization is needed to balance the difference in diffusive losses upstream and downstream of the expansion region. In our expanding helicon source experiments, we find that the upstream plasma density increases sharply at the same antenna frequency at which the double layer appears.
authors.affiliation: Department of Physics, West Virginia University, Morgantown, West Virginia 26506-6315, USA.
authors.forename: S Chakraborty
authors.initials: SC
authors.lastname: Thakur
authors.forename: Z
authors.initials: Z
authors.lastname: Harvey
authors.forename: I A
authors.initials: IA
authors.lastname: Biloiu
authors.forename: A
authors.initials: A
authors.lastname: Hansen
authors.forename: R A
authors.initials: RA
authors.lastname: Hardin
authors.forename: W S
authors.initials: WS
authors.lastname: Przybysz
authors.forename: E E
authors.initials: EE
authors.lastname: Scime