Langmuirprobeja

Langmuirprobeja, or Langmuir probes, are diagnostic devices used to measure basic parameters of a plasma by inserting a conducting electrode (the probe) into the plasma and biasing it with respect to a reference. As the bias voltage is swept, the collected current forms an I–V curve from which the plasma potential, electron temperature Te, and electron density ne can be inferred. The interpretation relies on the presence of a plasma sheath around the probe and on models of particle collection, often using orbital-motion-limited theory for small probes.

There are several probe configurations, including single probes, double probes (two electrodes), and emissive probes for direct plasma potential measurements. The electron current region and the ion-saturation region of the I–V curve provide estimates of Te and ne, while the plasma potential is approximated from the transition point between regimes or by the floating potential. Double and triple probes reduce perturbation to the plasma and allow more robust measurements in noisy or magnetized plasmas.

Langmuir probes are widely used in laboratory plasma research, fusion devices, space plasma experiments, and industrial plasmas such as semiconductor processing. Limitations include the perturbation of the plasma by the probe, inaccuracies in strongly magnetized or highly inhomogeneous plasmas, dependence on collisionality and probe geometry, and the need for careful calibration and suitable theoretical models. They remain a standard tool for rapid, in situ plasma diagnostics.