# Plasma Waves at Different Frequencies

I am trying to determine what plasma waves appear at what frequency ranges. Particularly, I am interested in exploring plasma waves occurring between 100kHz to 1MHz. Is this a bad frequency range to observe plasma waves if I plan on designing an instrument to measure them in the ionosphere. Should I look at another higher range of frequencies?

Waves in plasma is a very wide field of research. Numerous books have been written about that topic, see e.g. [1,2]. Actually a lot of research has been done on plasma waves in the ionosphere in the early time of plasma physics, see e.g. [3,4].

What type of waves can appear in a plasma depends on the plasma itself: the plasma density plays an important role, the collision frequency a well, and not to forget the background magnetic field. But maybe you know all this and just want to have an answer to your question, let my therefore try to answer it.

The ionosphere has an electron plasma density of $$n_e = 10^{10} - 10^{12}\,\mathrm{m}^{-3}$$ depending on daytime/nighttime and the height above ground. The resulting plasma frequency is in the MHz range which means that waves with higher frequencies can propagate across the ionosphere whereas waves with lower frequencies are reflected. Since you mentioned

100kHz to 1MHz

this is a range where you can make experiments in which you, for example, emit waves at such frequencies from ground and observe their reflected signals.

[1] Thomas Stix, Waves in Plasmas (1992)

[2] Donald Swanson, Plasma Waves (2003)

[3] K. Budden, Radio Waves in the Ionosphere (1961)