Plasma DriftIonized Gas / Plasma

Plasma Drift is a gas that stopped being polite.

Heat a gas enough, or hit it with enough radiation, and electrons come loose from their atoms. What remains is a mixture of free electrons and positive ions, and it behaves unlike any neutral gas, because every charged particle feels the others at a distance through electric and magnetic fields. Irving Langmuir named it plasma in 1928.

Its signature, the first formula on this page, is a collective oscillation. Nudge the electrons sideways and the ions, thousands of times heavier, stay put. The exposed charge pulls the electrons back, they overshoot, and the whole cloud rings at the plasma frequency, set only by how many free electrons there are per cubic metre. In Earth's ionosphere that frequency is a few megahertz. Radio waves below it cannot pass through and are turned back toward the ground, which is how shortwave broadcasts reach around the planet. Waves well above it pass out to space, which is why satellites talk to you at gigahertz.

The second formula is the Debye length: the distance over which a plasma hides any stray charge you put into it, by gathering a cloud of the opposite sign around it. A few Debye lengths away, the charge is invisible.

The third is the drift in Drift. Put a charged particle in crossed electric and magnetic fields and it does not simply fall along the electric field. It circles, and the circle creeps sideways at a speed E/B, at right angles to both fields. The answer contains neither the charge nor the mass. Electrons and ions, opposite in sign and thousands of times different in weight, drift together, in the same direction, at the same speed.

Drift does not go where you push. They go sideways, with everyone.