Question

What are thermal plasmas?
plasmas that have particles that collide infrequently
plasmas that reach a temperature equal to their surroundings
plasmas that do not reach thermal equilibrium
plasmas that have only a few particles ionized at any given moment

Answer 1

None of the provided options is correct.

Correct definition: a thermal plasma (often called an equilibrium or LTE plasma) is one in which the plasma species (electrons, ions, and neutrals) are in or close to thermal equilibrium with each other — i.e., they have (approximately) the same temperature because collisions are frequent enough to equilibrate them.

Why the choices are wrong
- "particles that collide infrequently": wrong — thermal plasmas have frequent collisions.
- "reach a temperature equal to their surroundings": wrong — thermal refers to internal equilibrium between species, not equality with the environment.
- "do not reach thermal equilibrium": wrong — that describes nonthermal (or cold) plasmas.
- "have only a few particles ionized": wrong — that describes weakly ionized plasmas; thermal plasmas can be strongly or moderately ionized.