Langmuir Probe
A diagnostic electrode inserted directly into a plasma to measure local electron temperature, plasma density, and floating potential from its current-voltage (I-V) curve.
Governing formula
I(V) = I_i,sat - I_e,sat exp(e (V - V_plasma) / (k_B T_e))
SI unit
A (Measured Current) & V (Bias Voltage)
In depth
Invented by Irving Langmuir. Sweeping bias voltage V on a small wire collector draws ion or electron current. Analyzing exponential region slopes yields electron temperature T_e and saturation currents yield electron density n_e.
Examples in the real world
Mapping edge plasma boundary density profiles in tokamaks and ionospheric satellite soundings.