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Journal Articles

Compensations of beamlet deflections for 1 MeV accelerator of ITER NBI

Kashiwagi, Mieko; Taniguchi, Masaki; Umeda, Naotaka; Dairaku, Masayuki; Tobari, Hiroyuki; Yamanaka, Haruhiko; Watanabe, Kazuhiro; Inoue, Takashi; DeEsch, H. P. L.*; Grisham, L. R.*; et al.

AIP Conference Proceedings 1515, p.227 - 236, 2013/02

 Times Cited Count:9 Percentile:94.55

In a five stage multi-aperture multi-grid (MAMuG) accelerator for the ITER neutral beam injector (NBI), 1 MeV, 40 A D$$^-$$ ion beam is required for 1 hour. However, beamlets are deflected due to (1) magnetic field for electron suppression and (2) space charge repulsion between beamlets, and consequently, cause excess grid heat load. A three dimensional beam analysis has been carried out to compensate the beamlet deflections. This paper shows that the beamlet deflections due to (1) and (2) are compensated by an aperture offset of only 0.6 mm applied to the aperture of 17 mm in diameter in the extractor and by a metal bar attached around aperture area beneath the extractor, respectively. When the metal bar is increased to 3 mm in thickness and installed 30 mm away from the aperture area, the beamlet is steered gently by the weaker electric field distortion. The beam optics was confirmed not deteriorated by those compensations. The presentation also discusses application of these compensation techniques to the ITER design.

Journal Articles

Analysis of electron temperature distribution by kinetic modeling of electron energy distribution function in JAEA 10 ampere negative ion source

Shibata, Takanori; Terasaki, Ryo*; Kashiwagi, Mieko; Inoue, Takashi; Dairaku, Masayuki; Taniguchi, Masaki; Tobari, Hiroyuki; Umeda, Naotaka; Watanabe, Kazuhiro; Sakamoto, Keishi; et al.

AIP Conference Proceedings 1515, p.177 - 186, 2013/02

 Times Cited Count:8 Percentile:94.55

In the neutral beam injector in JT-60SA, one of issues is that negative ion beam is partially intercepted at acceleration grids due to a spatial non-uniformity of negative ion production on large extraction area (0.9$$times$$0.45m$$^{2}$$). Previous experiments showed that fast electrons emitted from filament cathodes are transported in a longitudinal direction by $$mathbf{B} times textrm{grad} mathbf{B}$$ drift and the spatial distribution of electron temperature ($$T_e$$) strongly relates with the non-uniformity. In this study, a three-dimensional electron transport analysis has been developed. Electron temperature in the analysis agreed well with measurements in JAEA 10A ion source. This study clarified that the bias of $$T_e$$ distribution are caused by the following reasons; (1) fast electrons drifted in the longitudinal direction survives near the end wall with energy up to $$E$$ = 25-60 eV and (2) they produces thermal electrons by collision with plasma particles there.

Journal Articles

Study of negative hydrogen ion beam optics using the 2D PIC method

Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya; Kojima, Atsushi

AIP Conference Proceedings 1515, p.22 - 30, 2013/02

 Times Cited Count:8 Percentile:94.55

We have developed the integrated 2D PIC code for the analysis of the negative ion beam optics, in which an overall region from the source plasma to the accelerator is modeled. Thus, the negative ion trajectory can be solved self-consistently without any assumption of the plasma meniscus form initially. This code can reproduce the negative ion beam halo observed in an actual negative ion beam. It is confirmed that the surface produced negative ions which are extracted near the edge of the meniscus can be one of the reasons for the beam halo: these negative ions are over-focused due to the curvature of the meniscus. The negative ions are not focused by the electrostatic lens, and consequently become the beam halo.

Journal Articles

Study of plasma meniscus formation and beam halo in negative hydrogen ion sources

Okuda, Shin*; Miyamoto, Kenji*; Fukuyama, Toshishige*; Nishioka, Shu*; Hatayama, Akiyoshi*; Fukano, Azusa*; Hanada, Masaya; Kojima, Atsushi

AIP Conference Proceedings 1515, p.107 - 113, 2013/02

 Times Cited Count:9 Percentile:95.47

A meniscus of plasma-beam boundary in H$$^{-}$$ ion sources largely affects the extracted H$$^{-}$$ ion beam optics. Recently it is shown that the beam halo is mainly caused by the meniscus, i.e. ion emissive surface, close to the plasma grid (PG) where its curvature is large. The purpose of this study is to clarify the effect of H$$^{-}$$ surface production rate on plasma meniscus and beam halo formation with PIC (particle-in-cell) modeling. It is shown that the plasma meniscus and beam halo formation is strongly dependent on the amount of surface produced H$$^{-}$$ ions.

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