Beam optics in a MeV-class multi-aperture multi-grid accelerator for the ITER neutral beam injector

In a multi-aperture multi-grid accelerator of the ITER neutral beam injector, the beamlets are deflected due to space charge repulsion between beamlets and beam groups, and also due to magnetic field. Moreover, the beamlet deflection is influenced by electric field distortion generated by grid suppo...

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Bibliographic Details
Published in:Review of scientific instruments 2012-02, Vol.83 (2), p.02B119-02B119-3
Main Authors: Kashiwagi, M., Taniguchi, M., Umeda, N., de Esch, H. P. L., Grisham, L. R., Boilson, D., Hemsworth, R. S., Tanaka, M., Tobari, H., Watanabe, K., Inoue, T.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ACCELERATORS
ATOMIC BEAMS
BEAM INJECTION
BEAM OPTICS
Beams (radiation)
Deflection
ELECTRIC FIELDS
ELECTRONS
Injectors
ITER TOKAMAK
MAGNETIC FIELDS
METALS
MEV RANGE
Neutral beams
PARTICLE ACCELERATORS
SPACE CHARGE
Supports
THREE-DIMENSIONAL CALCULATIONS
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Summary:In a multi-aperture multi-grid accelerator of the ITER neutral beam injector, the beamlets are deflected due to space charge repulsion between beamlets and beam groups, and also due to magnetic field. Moreover, the beamlet deflection is influenced by electric field distortion generated by grid support structure. Such complicated beamlet deflections and the compensations have been examined utilizing a three-dimensional beam analysis. The space charge repulsion and the influence by the grid support structure were studied in a 1/4 model of the accelerator including 320 beamlets. Beamlet deflection due to the magnetic field was studied by a single beamlet model. As the results, compensation methods of the beamlet deflection were designed, so as to utilize a metal bar (so-called field shaping plate) of 1 mm thick beneath the electron suppression grid (ESG), and an aperture offset of 1 mm in the ESG.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.3673626