Beam optics studies for the planned hybrid electrostatic-magnetic guided slow positron beam in Hong Kong

Abstract

Design simulations are presented of a variable energy (0–40 keV) slow-positron beam that incorporates the convenience of magnetic guidance with the desirability of some electrostatic focusing produced by a lens structure operating in a low but increasing magnetic field region. Filtering of unmoderated positrons and gamma rays is to be accomplished using two conventionalE×B filters. In a novel way it is proposed that the final beam energy be adjusted using a simple linear de-acceleration stage and that the optimal electrostatic element potentials for efficient extraction, focusing and filtering of positrons be floated relative to the de-acceleration potential. The resulting intense and easily controllable sub-millimetre diameter beam should be suitable for both lateral and depth profiling of defects in semiconductor materials.