Neutral-beam performance analysis using a CCD camera

This paper discusses development of a diagnostic technique to measure (independent of the species mix of accelerated ions) the spatial distribution and absolute magnitude of the atomic-deuterium current produced by a natural-beam source. Using an absolutely calibrated CCD (charge-coupled device) video camera, the authors view the natural beam as it passes through a relatively high pressure (10-5 Torr) region outside the neutralizer: collisional excitation of the energetic neutrals produces a Dα emission (6561 angstrom) that is proportional to the local atomic current density. For the energy range of interest (5 keV>E>20 keV), the excitation rate coefficient is nearly constant to obtain the local atomic current regardless of the fraction of full, half, and third energy components. Digital processing of the video signal provides profile and aiming information for beam optimization. Results are compared with those obtained from a Faraday cup and infrared imaging of the beam dump