An injector based on electric insulation for the controlled ballistic focusing of light ion beams

An injector design is described which uses a space‐charge‐limited source of alkali ions and accelerates the ions through two stages of acceleration and slight deceleration stage (to retard the neutralizing electrons) before matched phase space neutralization with an electron reflex triode source occurs. For typical conditions of a 200‐ns pulse and a 1‐MeV 1‐10 A/cm2 lithium ion beam, computer simulation experiments demonstrate that 55% of the beam trajectories have an angular divergence less than 250 μrad (thereby meeting an order of magnitude more stringent constraint at more than an order of magnitude higher power density than any previous electrostatically focused injector design). The method of achieving the low angular divergence profile at readily attainable voltages of 200 kV, current densities of 150 mA/cm2, and vacuum stresses of 50 kV/cm is described. By simply increasing the voltage towards 1 MV, state‐of‐the‐art advances in all the parameter areas can be made without altering the angular diver...