Collected Current by a Double Langmuir Probe Setup With Plasma Flow

The multineedle Langmuir probe (m-NLP) instrument, consisting of two or more fixed-bias cylindrical Langmuir probes, is designed to enhance data resolution, particularly for in situ measurement in space missions. However, like other spacecraft and instruments used in space missions, these probes may interact with the surrounding plasma, potentially leading to errors in plasma measurements. In this article, we investigate the interaction between a double Langmuir probe setup and plasma flow, specifically focusing on how the collected current on the probes is affected by the electric bias and varying distances between the probes. Results from Particle-in-Cell (PIC) simulations show that with a front probe and a rear probe aligned along the plasma flow, not only may the rear probe’s collected current be affected, but the entire system may also experience significant influences if the distance between probes is short. In particular, if both probes are positively biased, as in the m-NLP instrument, they will not significantly influence each other’s measurements if the distance between them is longer than 30 Debye lengths. We also employ test particle simulations to further illustrate the interaction between the double Langmuir probe system and its surrounding plasma.