Novel directional ion energy analyzer

A new ion energy analyzer with high angular resolution (⩽3×10−4 sr) is described. It consists of a microchannel plate followed by a retarding‐grid type analyzer. The microchannel plate is not used for charge multiplication but as a geometric filter with narrow angular passband (ϑ≃0.6°) yet high transparency (T≃60%). The energy analyzer is used to measure the true velocity space distribution of low‐energy ion beams (Eb = 10–100 eV) in a double plasma device. Its superior performance over the conventional gridded energy analyzer is demonstrated. Applications to the study of beam wakes are shown.