Editing Langmuir probe (section)

===Single probe===

The most straightforward way to measure the ''I-V'' characteristic of a plasma is with a '''single probe''', consisting of one electrode biased with a voltage ramp relative to the vessel. The advantages are simplicity of the electrode and redundancy of information, i.e. one can check whether the ''I-V'' characteristic has the expected form. Potentially additional information can be extracted from details of the characteristic. The disadvantages are more complex biasing and measurement electronics and a poor time resolution. If fluctuations are present (as they always are) and the sweep is slower than the fluctuation frequency (as it usually is), then the ''I-V'' is the ''average'' current as a function of voltage, which may result in systematic errors if it is analyzed as though it were an instantaneous ''I-V''. The ideal situation is to sweep the voltage at a frequency above the fluctuation frequency but still below the ion cyclotron frequency. This, however, requires sophisticated electronics and a great deal of care.