A Velocity Filter for Electrons and Ions

Abstract

If a charged particle, moving along the x-axis with a velocity v, encounters successively two identical alternating electric fields of frequency ν, which are everywhere perpendicular to the x-axis, it will emerge from the last field undisplaced and traveling in the original direction under the following conditions: (1) Each field has two similar halves whose distance between centers is a; (2) The distance between the fields, center to center, is D=sa/n, where s and n are odd integers; (3) The velocity of the particle is v_0=2aν/n. The distribution about the velocity v_0 is computed when particles enter and leave the system through slits of width y_0 on the x-axis. The results show that the emergent beam can be confined to a very narrow velocity range.

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