Spectroscopic determination of species and divergence of hydrogen beams in the W7AS neutral beam injectors
Light-collecting systems are installed at the neutralisers of the W7AS neutral beam lines. They receive light emitted at an angle of 120 to the beam axes. Hydrogen beams are analysed at around the wavelength of H(alpha) (6562.8 Angstrom), helium beams at around 5875.6 Angstrom. The hydrogen spectra show the well-known shifted and unshifted lines emitted by the different beam species and the background gas. The line widths are mainly determined by the beam focusing, the beamlet divergence and the apparatus profile. Knowing the focusing properties of the ion source and the instrument function of the spectrometer, the beamlet divergence can be determined. The spectrum is approximated by a series of Gaussians using least-squares fitting methods and evaluated with respect to beam species and divergence. Evaluation of the spectra proved difficult because they show a structured background, which is observed in the whole range of the Doppler shift. It is shown with helium beams that the background is caused by wall reflection of light emitted by the beam in the whole angular range between 0 and 180 . The knowledge of the background structure gained with He beams allows interpretation of the more complicated hydrogen spectra.
Bibliographic Reference: Report: IPP 4/258 EN (1993) 24 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199310460 / Last updated on: 1994-11-29
Original language: en
Available languages: en