Ion dynamics in standing electromagnetic wave near the cyclotron resonance

The dynamics of ions under the forces exerted by a planar standing electromagnetic wave near the cyclotron resonance is studied. It is shown that ions whose cyclotron frequency is larger than the wave frequency are pushed by the ponderomotive force toward and oscillate around the wave magnetic node, while ions whose cyclotron frequency is smaller than the wave frequency are pushed to and oscillate around the wave electric node. When the difference between the cyclotron frequency and the wave frequency is large, the ion motion is governed by a time independent ponderomotive potential. When that difference is small, the ion oscillates around the wave magnetic node with varying-in-time amplitude and frequency, described approximately by solutions of the Mathieu equation. Difficulties in using such a configuration for mass separation are discussed. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-Non Commercial 4.0International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).