title: Development of a low-energy and high-current pulsed neutral beam injector with a washer-gun plasma source for high-beta plasma experiments.
abstract: We have developed a novel and economical neutral-beam injection system by employing a washer-gun plasma source. It provides a low-cost and maintenance-free ion beam, thus eliminating the need for the filaments and water-cooling systems employed conventionally. In our primary experiments, the washer gun produced a source plasma with an electron temperature of approximately 5 eV and an electron density of 5 × 10(17) m(-3), i.e., conditions suitable for ion-beam extraction. The dependence of the extracted beam current on the acceleration voltage is consistent with space-charge current limitation, because the observed current density is almost proportional to the 3/2 power of the acceleration voltage below approximately 8 kV. By optimizing plasma formation, we successfully achieved beam extraction of up to 40 A at 15 kV and a pulse length in excess of 0.25 ms. Its low-voltage and high-current pulsed-beam properties enable us to apply this high-power neutral beam injection into a high-beta compact torus plasma characterized by a low magnetic field.
authors.affiliation: Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan. ii@ts.t.u-tokyo.ac.jp
authors.forename: Toru
authors.initials: T
authors.lastname: Ii
authors.forename: Keii
authors.initials: K
authors.lastname: Gi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Umezawa
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Asai
authors.forename: Michiaki
authors.initials: M
authors.lastname: Inomoto
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ono