Langmuir probe


The Langmuir probe APS3, Institute of Electrical Engineering and Plasma Technology at the Ruhr-Universität Bochum, Bochum, Germany, is a device for the spatially resolved characterization of plasma-based coating processes. The probe is a cylindrical electrode in the plasma to which a potential is applied. Due to the contact with the plasma, this potential is pulled onto the surface of the probe, whereby the characteristic U-I curve, also called probe characteristic curve, can be measured. This characteristic curve can be measured either with time or spatial resolution. For a measurement with the Langmuir probe, the Debye length must be small compared to the plasma expansion and the electrode temperature Te must be as high as possible compared to the ion temperature Ti. If these criteria are fulfilled, the electron density, the mean electron energy, the plasma potential and the energy distribution of the electrons and the floating potential can be measured.

Technical data:

Parameter Value [Unit]
Effective Current range

±1 µA to ±100 mA (16 Bit Resolution)

Characteristic curve range from -80 V to 80 V (Resolution 2.44 mV)
Floating Potential from 0 V to +320 V (Resolution 78.12 mV)
Sampling Frequency 51.2 kHz