Detailed explanations of the concepts may be found in almost any text on plasma physics. Since most of these books are almost totally incomprehensible to the average mortal, a suggestion will be made at the end of the article. The second experiment, as adapted by Jones, is diagrammed in Figure 1. I note this experiment because of the importance of the Langmuir probe in plasma diagnostics. A Langmuir probe is nothing more than a wire that is inserted into a plasma to measure its potential.
Early experimenters let the probe float and measured the voltage with a high impedance meter.
That gave totally erroneous measurements because the floating probe would permit charges to accumulate. Langmuir's technique involved connecting the probe to a source of variable potential. The probe voltage is swept and the resulting current vs. voltage characteristic will yield the electron and ion currents to the probe. The figure shows how the OA4-G is connected for this experiment. A discharge is triggered between the cylindrical cathode at pin 2 and a ring shaped anode at pin 7.