Plasma Drift: Ionized Gas / Plasma
Electromagnetism & Plasma arc, page 84 of 193. Back to The Pixelated Physics Universe
Who they are
Heat a gas far enough and its atoms come apart. Plasma is ionized gas: free electrons and ions, found in stars, lightning and neon signs. Meet Plasma Drift, named for the E × B drift: in crossed electric and magnetic fields, electrons and ions circle in opposite directions yet drift together, the same way at the same speed, v = E/B. Plasma Drift wears it in pixel art on a unisex tee.
Plasma Drift is a character of the Electromagnetism & Plasma arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
In a plasma, electrons that are pushed aside spring back and oscillate at the plasma frequency, which depends only on how dense they are. Charges also screen each other beyond the Debye length, and in crossed electric and magnetic fields the whole plasma drifts sideways at E/B.
$$ \begin{gathered} \omega_p = \sqrt{\frac{n_e e^{2}}{\varepsilon_0 m_e}} \\ \lambda_D = \sqrt{\frac{\varepsilon_0 k_B T_e}{n_e e^{2}}} \\ \vec v_E = \frac{\vec E \times \vec B}{B^{2}} \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $\omega_p$ | electron plasma frequency | rad/s |
| $n_e$ | electron number density | m⁻³ |
| $e$ | elementary charge | C |
| $\varepsilon_0$ | vacuum permittivity | F/m |
| $m_e$ | electron mass | kg |
| $\lambda_D$ | Debye length | m |
| $k_B$ | Boltzmann constant | J/K |
| $T_e$ | electron temperature | K |
| $\vec v_E$ | E×B drift velocity | m/s |
| $\vec E$ | electric field | V/m |
| $\vec B$ | magnetic field | T |
Sources
- Langmuir (1928) Oscillations in Ionized Gases, PNAS 14, 627
- Encyclopaedia Britannica — Plasma (state of matter)
- NIST CODATA 2022 — elementary charge e
- NIST CODATA 2022 — vacuum electric permittivity ε0
- NIST CODATA 2022 — electron mass energy equivalent in MeV
Crossovers
Plasma Drift meets Shielda (Debye Shielding). Plasma Drift is a gas of free charges. Shielda is what those charges do to any one of them: they gather round it and screen its field beyond the Debye length.
Plasma Drift meets Alfvena (Alfvén Waves). Plasma Drift's charges circle magnetic field lines and drift across them in crossed fields. Alfvena treats the same field lines as strings under tension; in a plasma, the charges and the field move together.
Plasma Drift meets Ignia (Lawson Criterion). Plasma Drift's E × B drift and other particle motions in magnetic fields decide how well a plasma is confined. Ignia needs that confinement to be good enough to pass the Lawson triple product for fusion.
Wear the lore
- Plasma Drift – Ionized Gas / Plasma Physics T-Shirt
- Related infographic poster: The Magnetic Bottle – Plate 078 Physics Poster
Concept keywords: Ionized Gas / Plasma, Plasma Drift, Electromagnetism & Plasma, physics lore, Pixelated Physics