A second type of electrostatic converter initially proposed by Post, then developed by Barr and Moir, is the Periodic Electrostatic Focusing concept. Like the Venetian Blind concept, it is also a direct collector, but the collector plates are disposed in many stages along the longitudinal axis of an electrostatic focusing channel. As each ion is decelerated along the channel toward zero energy, the particle becomes "over-focused" and is deflected sideways from the beam, then collected. The Periodic Electrostatic Focusing converter typically operates with a 600 keV D-T plasma (as low as 400 keV and up to 800 keV) with efficiency of about 60% under conditions compatible with economics, and an upper technical conversion efficiency up to 90% ignoring economic limitations.