Adding a static magnetic field to an RF-excited plasma has two major consequences. Firstly, the plasma transport is reduced in the direction perpendicular to the magnetic field lines; this will be discussed in the next chapter. It will be shown that the magnetic field reduces the transverse plasma flux and may therefore be used to increase the plasma density at given power. More generally, the addition of a static magnetic field can be used to adjust the uniformity of the plasma flux, and to modify the electron temperature or the electron energy distribution function. This is achieved by changing the magnetic field topology. Some of these properties are used in magnetically enhanced reactive ion etching (MERIE) reactors, which are capacitively coupled reactors with a magnetic field parallel to the electrodes. In some instances, this magnetic field is designed to rotate at low speed in order to average out modest asymmetries of the plasma parameters.

Secondly, a static magnetic field enables the propagation of electromagnetic waves at low frequencies, that is at ω « ωpe; a class of such waves, known as ‘helicons’, are of particular importance in plasma processing and in space plasma propulsion. Helicons are part of a bigger group of waves called ‘whistlers’. The first report of whistlers, that is whistling tones descending in frequency from kilohertz to hundreds of hertz in a few seconds, was in the early twentieth century.