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3) Waves in plasmas

We all know the basic nature of electromagnetic waves in vacuum, as well as their importance for our modern world (telecommunications, RADARS, weather forecast etc.)

How would this picture be modified if we try to send electromagnetic waves through a plasma?

Any relatively thorough discussion of this topic would be technical and very long, since one has to distinguish between several situations (cold or warm plasma, magnetized or not etc.)

We will present a few characteristic cases, trying to give a somewhat intuitive interpretation, rather than go into complicated mathematical formulas.

But wait a minute! Why do we even care about waves in plasmas? We aren’t going to build a radio station on the sun, are we?

We certainly are not, but we will build a sun on earth! That’s right, plasma waves play an important role in thermonuclear fusion, which has very good chances of solving the world’s energy problem once and for all! Furthermore in the old days (before satellites), people used to send AM waves bouncing off the ionosphere, to transmit signals in long distances despite the curvature of the earth!

Finally, the whole “radio station on the sun” business might seem funny, but it certainly is not! The interaction of waves with plasma is very important for astrophysics!

Let’s start our discussion about waves! Since we already discovered plasma oscillations, it is both a good place to start and a topic that has an important subtlety.