Ion beam divergence in two stage acceleration

Numerical results on the angular beam divergence in two-stage ion source are given for the second stage composed of a spherically concave electrode and a disk aperture exit electrode, assuming the concave electrode as a homogeneous beam emitting electrode. The geometry of the electrode is optimized to yield a low divergence beam for the aspect ratios of 1 and 2/3, the ratios of the initial acceleration energy to the final beam energy of 1/3 and 1/2, and the perveance of 0.6 to 1.5. It is found that the beam divergence increases rapidly with the perveance above a certain value and that the final beam divergence increment due to the first stage divergence is equal to the beam divergence of the first stage. (auth.)