Plasma physics

Equipment

• Virtual plasma slab with ions and electrons
• Sliders for density nₑ and displacement amplitude
• Readout of ω_pe and λ_D relations

Procedure

1. Excite plasma oscillations

   In figure 1 "Collective oscillation", watch the electron layer displaced from the ion background and pulled back — producing Langmuir oscillations. Change "Displacement amplitude": oscillations grow but the frequency stays nearly fixed: $\omega_{pe}$ is a property of the medium, not the amplitude (ignoring nonlinear corrections).

2. Check ω_pe ∝ √nₑ

   Raise "Relative density nₑ" by ×4 and read the readout: the characteristic frequency doubles — confirming $\omega_{pe} = \sqrt{n_e e^2/(\varepsilon_0 m_e)}$. Meanwhile the Debye length shrinks: $\lambda_D = \sqrt{\varepsilon_0 k_BT_e/(n_e e^2)}$ — a denser plasma screens fields better.

3. Connect to real plasmas

   In figure 2, compare the trend with real values: Earth's ionosphere ($n_e \sim 10^{11}\!-\!10^{12}$ m⁻³, ω_pe of a few MHz — why AM radio reflects), tokamaks ($n_e \sim 10^{20}$ m⁻³, ω_pe in the 100 GHz range), stellar cores. Note: the plasma frequency sets a "floor" — EM waves with $\omega < \omega_{pe}$ cannot propagate through plasma.

Simulation

Experiment history

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