Measurement of Deuterium Beam Energy Distribution and Species Using an Electrostatic Energy Analyzer

The peak energy, energy broadening, and neutral current fractions for the E, E/2, and E/3 energy components of the prototype Tokamak Fusion Test Reactor 120-keV deuterium neutral beam source were measured on the Neutral Beam System Test Facility at Lawrence Berkeley Laboratory using a 127-deg swept electrostatic energy analyzer provided by the Princeton Plasma Physics Laboratory. The results were compared with Doppler shift spectroscopy measurements, taking into account the different geometrical factors for both methods. The average neutral current fractions for the E, E/2, and E/3 atomic species components measured with the electrostatic analyzer and extrapolated to the target area were 0.35, 0.47, and 0.18, respectively, which agreed with the spectroscopic results to within 5%. For all species, a 1/e full-width energy broadening of ∆.E/E ≅ 4% was observed for an analyzer energy resolution of both ∼4 and 1%. This width is not in contradiction with the energy broadening expected due to Franck-Condon dissociation effects. The peak energies for the E, E/2, and E/3 components were within ∼4% of the rated values, but consistently on the low side of the standard deviation.