title: Characterization of the CW starter plasma RF matching network for operating the SNS H⁻ ion source with lower H₂ flows.
abstract: The Spallation Neutron Source H(-) ion source is operated with a pulsed 2-MHz RF (50-60 kW) to produce the 1-ms long, ∼50 mA H(-) beams at 60 Hz. A continuous low power (∼300 W) 13.56-MHz RF plasma, which is initially ignited with a H2 pressure bump, serves as starter plasma for the pulsed high power 2-MHz RF discharges. To reduce the risk of plasma outages at lower H2 flow rates which is desired for improved performance of the following radio frequency quadrupole, the 13.56-MHz RF matching network was characterized over a broad range of its two tuning capacitors. The H-α line intensity of the 13.56-MHz RF plasma and the reflected power of the 13.56-MHz RF were mapped against the capacitor settings. Optimal tunes for the maximum H-α intensity are consistent with the optimal tunes for minimum reflected power. Low limits of the H2 flow rate not causing plasma outages were explored within the range of the map. A tune region that allows lower H2 flow rate has been identified, which differs from the optimal tune for global minimum reflected power that was mostly used in the past.
authors.affiliation: Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: B X
authors.initials: BX
authors.lastname: Han
authors.affiliation: Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Stockli
authors.affiliation: Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Kang
authors.affiliation: Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: C
authors.initials: C
authors.lastname: Piller
authors.affiliation: Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: S N
authors.initials: SN
authors.lastname: Murray
authors.affiliation: Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: T R
authors.initials: TR
authors.lastname: Pennisi
authors.affiliation: Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: M
authors.initials: M
authors.lastname: Santana
authors.affiliation: Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: R F
authors.initials: RF
authors.lastname: Welton