title: Reduction of plasma density in the Helicity Injected Torus with Steady Inductance experiment by using a helicon pre-ionization source.
abstract: A helicon based pre-ionization source has been developed and installed on the Helicity Injected Torus with Steady Inductance (HIT-SI) spheromak. The source initiates plasma breakdown by injecting impurity-free, unmagnetized plasma into the HIT-SI confinement volume. Typical helium spheromaks have electron density reduced from (2-3) × 10(19) m(-3) to 1 × 10(19) m(-3). Deuterium spheromak formation is possible with density as low as 2 × 10(18) m(-3). The source also enables HIT-SI to be operated with only one helicity injector at injector frequencies above 14.5 kHz. A theory explaining the physical mechanism driving the reduction of breakdown density is presented.
authors.affiliation: Department of Aeronautics and Astronautics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Aaron C
authors.initials: AC
authors.lastname: Hossack
authors.forename: Taylor
authors.initials: T
authors.lastname: Firman
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Jarboe
authors.forename: James R
authors.initials: JR
authors.lastname: Prager
authors.forename: Brian S
authors.initials: BS
authors.lastname: Victor
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Wrobel
authors.forename: Timothy
authors.initials: T
authors.lastname: Ziemba