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Report No.

Improvement of uniformity of the negative ion beams by Tent-shaped magnetic field in the JT-60 negative ion source

Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Grisham, L. R.*; Akino, Noboru; Endo, Yasuei; Komata, Masao; Mogaki, Kazuhiko; Nemoto, Shuji; Ozeki, Masahiro; Seki, Norikatsu; Sasaki, Shunichi; Shimizu, Tatsuo; Terunuma, Yuto

Non-uniformity of the negative ion beams in the JT-60 negative ion source was improved by modifying an external magnetic field to a tent-shaped magnetic field for reduction of the local heat loads in the source. Distributions of the source plasmas (H$$^{+}$$ ions and H$$^{0}$$ atoms) of the parents of H$$^{-}$$ ions converted on the cesium covered plasma grids were measured by Langmuir probes and emission spectroscopy. Beam intensities of the H$$^{-}$$ ions extracted from the plasma grids were measured by IR camera from the back of the beam target plate. The tent-shaped magnetic field prevented the source plasmas to be localized by B $$times$$ grad B drift of the primary electrons emitted from the filaments in the arc chamber. As a result, standard derivation of the H$$^{-}$$ ions beams was reduced from 14% (the external magnetic field) to 10% (the tent-shaped magnetic field) without reduction of an activity of the H$$^{-}$$ ion production.



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Category:Instruments & Instrumentation



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