Effects on Langmuir probe characteristics owing to the finite impedance between the bulk plasma and the probe reference

An experimental investigation on Langmuir probe measurements in a magnetized plasma column with two-temperature electron population in argon discharge is presented. Especially, the effect of finite impedance between the bulk plasma and the probe reference on the resulting I(U) traces has been emphasised with the help of an electrical analogy. It is a known fact that probe I(U) traces follow the usual exponential law if the measurements are performed with a reference electrode in good contact with plasma, which is usually a grounded discharge electrode. However, in the present case it is shown that when the grounded probe reference is not a part of the discharge circuit there exist a finite impedance between the probe reference and bulk plasma. This impedance effect is eventually reflected in the measured probe I(U) traces especially in terms of the lower values of electron saturation current as compared to the ideal scenario. An appropriate correction is thus required to account actual electron saturation current and thereby to extract subsequent plasma parameters. Therefore, a simple electrical analogy has been proposed to interpret appropriate correction factors to the probe I(U) traces resulting from such magneto-plasma devices, where reference to the probe is in partial or poor contact with the bulk plasma.