Langmuir probe

A Langmuir probe is a device used to determine the electron temperature, electron density, and electric potential of a plasma. It works by inserting one or more electrodes into a plasma, with a constant or time-varying electric potential between the various electrodes or between them and the surrounding vessel. The measured currents and potentials in this system allow the determination of the physical properties of the plasma.

The beginning of Langmuir probe theory is the I-V characteristic of the Debye sheath, that is, the current density flowing to a surface in a plasma as a function of the voltage drop across the sheath. The analysis presented here indicates how the electron temperature, electron density, and plasma potential can be derived from the I-V characteristic. In some situations a more detailed analysis can yield information on the ion density (${\displaystyle n_{i}}$), the ion temperature ${\displaystyle T_{i}}$, or the electron energy distribution function (EEDF) or ${\displaystyle f_{e}(v)}$.

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