A new probe for measuring small electric fields in plasmas

A dipolar double probe has been developed for in situ measurements of small electric fields in laboratory plasmas. The probe measures dc to ac electric fields (0≤f≲20 MHz) with high sensitivity (Emin≂10 μV/cm) and responds to both space charge electric fields (Esc(Esc= −∇φp) and inductive electric fields (Ei = −∂A/∂t). Using voltage-to-frequency conversion, the probe signal is obtained free of errors and loading effects by a transmission line. Various examples of useful applications for the new probe are presented, such as measurements of (i) dc ambipolar fields, (ii) ac space-charge fields of ion acoustic waves, (iii) ac inductive fields of whistler waves, and (iv) mixed inductive and space-charge electric fields in current-carrying magnetoplasmas.