Thermal vs Non-Thermal Plasma: Two Temperatures

In a plasma the light electrons and the heavy gas particles need not share a temperature. Choose a regime and raise the input power — the animated gap shows the particles themselves, and the bars below track their two temperatures as they diverge or converge.

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Animated microscopic view of a discharge gap: small fast electrons dart between two electrode plates while large heavy gas particles drift slowly; when an electron strikes a heavy particle it bounces off with only a tiny energy transfer and a brief excitation flash. Below, two thermometer bars track electron temperature and gas temperature: in the non-thermal regime the electron bar rises far above the gas bar, in the thermal regime both rise together.
Electron temp Te
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Gas temp Tg
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500 K reference
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The physics. An electric field accelerates the light electrons far more effectively than the heavy ions. In a low-pressure or short-pulse discharge, electrons reach 1–10 eV (tens of thousands of kelvin as an equivalent temperature) while transferring little energy per collision to the heavy particles, so the gas stays near room temperature — this is cold plasma. At sufficiently high power density and collisionality, frequent collisions let electrons and heavy particles approach thermal equilibrium at 10,000–20,000 K: a thermal plasma. In the animated gap, particle speed represents temperature: watch an electron strike a heavy particle — it ricochets away while the heavy particle barely moves, and the brief flash marks collisional excitation, the process that makes real plasmas glow. The 500 K line is an illustrative reference only — real material limits vary widely, and living tissue or many polymers can be damaged well below it. Values and motion are representative teaching-scale figures, not measurements of a specific device.