That physicists brought to an eager mankind...
First, strong magnets are used to confine
Electrons, and cause them to travel in line.
Then a microwave signal is also injected
And in a slow-wave circuit its course is deflected,
So that, in the axial direction its speed is made slower,
To first bunch the beam, then extract from it power.
And when all this is cleverly thought out and done,
You can talk via satellite link on your phone!...