Comparison of fluctuations properties measured by Langmuir and ball-pen probes in the ISTTOK boundary plasma

In this work, the fluctuations properties measured by Langmuir and ball-pen probes are compared, aiming at investigating the influence of temperature fluctuations on Langmuir probe measurements, including the cross-field turbulent particle flux. With this aim, a 5-pin probe was designed to estimate the radial particle transport due to fluctuations simultaneously using Langmuir and ball-pen probes. A considerable difference is observed in the amplitude of the floating potential fluctuations measured by the two types of probes, but not in statistical properties such as skewness. The turbulent particle flux was found to be roughly four times larger when measured with Langmuir probes. Finally, it is suggested that ball-pen and emissive probes may underestimate the amplitude of the plasma potential fluctuations and therefore probe measurements must be carefully validated.