is retracted until its potential saturates. The resulting potential is above the Langmuir probe potential. Electron temperature measurements Using two measurements of the plasma potential with probes whose coefficient differ, it is possible to retrieve the electron temperature passively (without any input voltage or current). Using a Langmuir probe (with a non-negligible) and a ball-point probe (whose associated is close to zero) the electron temperature is given by: where is measured by the ball-pen probe, by the standard Langmuir probe, and is given by the Langmuir probe geometry, plasma gas composition, the magnetic field, and other minor factors (secondary electron emission, sheath expansion, etc.) It can be calculated theoretically, its value being about 3 for a non-magnetized hydrogen plasma. In practice, the ratio for the ball-pen probe is not exactly equal to one, so that the coefficient must be corrected by an empirical value for : where References External links PhD thesis, Jiri Adamek (Czech and English language) Overview: Ball-pen probe design, theory and first results at different fusion devices. Examination of plasma current spikes and general analysis of H-mode shots in the tokamak COMPASS Electrical Probe Measurements on the COMPASS Tokamak Probe Measurements on the COMPASS Tokamak Scanning ion sensitive probe for plasma profile measurements in the boundary of the Alcator C-Mod tokamak Development of Probes for Assessment of Ion Heat Transport and Sheath Heat Flux in the Boundary of the Alcator C-Mod Tokamak Video: Temporal evolution of Type-I ELM in the divertor region on the COMPASS tokamak. The new divertor Ball-pen and Langmuir probes on the COMPASS tokamak. Plasma diagnostics