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Author(s):
Y. Oka, O. Kaneko, K. Tsumori, Y. Takeiri, M. Osakabe, T. Kawamoto, E. Asano, and R. Akiyama
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Title:
H- Ion Source Using a Localized Virtual Magnetic Filter in the Plasma Electrode: Type I LV Magnetic Filter
Date of publication:
Dec. 1999
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Key words:
hydrogen negative ion, ion source, magnetic filter, cesium deposition, NBI
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Abstract:
A new multicusp H^- ion source using a Localized Virtual magnetic filter of type I [Ref.6] in the plasma electrode is investigated. A multipole (MP) arrangement with a spacing of 10 mm of the magnet bars holds an extraction hole, optimizing the efficient production of high H^- current, and at the same time only a small electron component was co-extracted with the H^- ions. The local filter arrangement separates the beam electrons at a low energy. It is shown that the co-extracted total electron current is determined principally by the integrated magnetic field flux (Gcm) of the local filter with an extraction system at a constant extraction voltage. When the value of the Gcm is increased, the total electron component is reduced, while the H^- electrical efficiency had a braod maximum around the optimized value of the Gcm. A thicker plasma electrode should be necessary for sufficient reduction of electron current. In pure hydrogen operation, the achieved current density of H^- is 10 mA/cm^2. when Cs was seeded in a filter optimized for pure volume mode H^- production, the maximum H^- current density obtained is 51 mA/cm^2 and the ratio I_ele/H^- is ~ 0.4 without applying a bias potential.
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