title: Enhanced surface production in H- ion sources by introducing a negatively biased secondary electrode.
abstract: A transformer coupled plasma negative hydrogen ion source with an external rf antenna has been developed at SNU, which is capable of continuous operation with long lifetime. A positively biased plasma electrode (PE) has been successfully used for the optimization of H(-) extraction. With molybdenum-coated stainless steel PE, the enhancement of H(-) production at the electrode surface was observed at the bias voltage lower than the plasma potential. However, the low bias voltage is unfavorable to H(-) beam extraction since the negative ions are repelled. A second electrode is inserted in front of the PE to enhance H(-) production at the electrode surface without impeding beam extraction. By biasing the secondary electrode (SE) more negatively, H(-) production is clearly enhanced although the SE itself reduces H(-) beam currents because of suppressed electron transport in front of the PE. In this configuration enhancement of surface productions is most pronounced in tantalum electrode among various electrode materials.
authors.affiliation: Department of Nuclear Engineering, Seoul National University, Seoul 151-742, Republic of Korea.
authors.forename: YoungHwa
authors.initials: Y
authors.lastname: An
authors.forename: BongKi
authors.initials: B
authors.lastname: Jung
authors.forename: Y S
authors.initials: YS
authors.lastname: Hwang