Electron cyclotron resonance
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A plasma may be efficiently produced by superimposing a static magnetic field and a high frequency electromagnetic field at the electron cyclotron resonance frequency.
An electron in a static and uniform magnetic field will move in a circle. The circular motion may be superimposed with a uniform axial motion, resulting in a helix, or with a uniform motion perpendicular to the field, e.g., in the presence of an electrical or gravitational field, resulting in a cycloid. The frequency of this cyclotron motion is given by
- <math>\omega_{ce}=\frac{eB}{m}<math>.
For the commonly used microwave frequency 2.45 GHz, the resonance condition is met when B = 875 G = 0.0875 T.