title: Negative ion production and beam extraction processes in a large ion source (invited).
abstract: Recent research results on negative-ion-rich plasmas in a large negative ion source have been reviewed. Spatial density and flow distributions of negative hydrogen ions (H(-)) and positive hydrogen ions together with those of electrons are investigated with a 4-pin probe and a photodetachment (PD) signal of a Langmuir probe. The PD signal is converted to local H(-) density from signal calibration to a scanning cavity ring down PD measurement. Introduction of Cs changes the slope of plasma potential local distribution depending upon the plasma grid bias. A higher electron density H2 plasma locally shields the bias potential and behaves like a metallic free electron gas. On the other hand, the bias and extraction electric fields penetrate in a Cs-seeded electronegative plasma even when the electron density is similar. Electrons are transported by the penetrated electric fields from the driver region along and across the filter and electron deflection magnetic fields. Plasma ions exhibited a completely different response against the penetration of electric fields.
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tsumori
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Nakano
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kisaki
authors.affiliation: The Graduate University for Advanced Studies, Shonan Village, Hayama, Kanagawa 240-0193, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Geng
authors.affiliation: Graduate School of Science and Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Wada
authors.affiliation: Division of Quantum Science and Engineering, Hokkaido University, Sapporo 060-8628, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Sasaki
authors.affiliation: Division of Quantum Science and Engineering, Hokkaido University, Sapporo 060-8628, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Nishiyama
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Goto
authors.affiliation: Plasma Engineering Group, Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Serianni
authors.affiliation: Plasma Engineering Group, Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Agostinetti
authors.affiliation: Plasma Engineering Group, Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Sartori
authors.affiliation: Plasma Engineering Group, Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Brombin
authors.affiliation: Plasma Engineering Group, Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Veltri
authors.affiliation: Max-Planck-Institut für Plasmaphysik, Bereich ITER-Technologie und -Diagnostik/N-NBI Boltzmannstr. 2, 85748 Garching, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Wimmer
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Nagaoka
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Osakabe
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Takeiri
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: O
authors.initials: O
authors.lastname: Kaneko