Space and time resolved doppler spectroscopy of neutral beams

Doppler shifted Balmer-α light emission originating from collisions of neutral hydrogen beams with residual gas molecules is a method commonly used to measure species composition of hydrogen ions (H+, H2+ and H3+) extracted from high power ion sources [1-3]. Species composition is derived from the ratio of emission intensities corresponding to full, half and third energy fractions, while the width of the emission lines provides information on beam divergence. Light is usually collected from a region close to the beam centre line, focused on a single optical fibre and transported to optical monochromator. Parameters determined in this way reflect the average values integrated across the beam along the single line of sight. A new multi-channel Balmer-α diagnostic was recently commissioned at JET Neutral Beam Test Bed, which allows spatially resolved measurements of various beam parameters. (author)