First results from the Langmuir Probes on the Swarm satellites

Langmuir Probes (LP) are well-proven simple instruments allowing to estimate the electron density (Ne) and temperature (Te) of a plasma. They are also used to estimate the electric potential of satellites to the benefit of other instruments and technical systems. On the Swarm satellites the LPs are part of the Electric Field Instruments (EFI) featuring thermal ion imagers (TII) measuring 3-d ion distributions. The main task of the Langmuir probes is to provide measurements of spacecraft potentials influencing the ions before they enter the TIIs. In addition also electron density (Ne) and temperature (Te) are estimated from EFI LP data. The design of the Swarm LP includes a standard current sampling under sweeps of the bias voltage, and also, for most of the time, a novel ripple technique yielding derivatives of the current-voltage characteristics at three points in a rapid cycle. In normal mode the time resolution of the Ne and Te measurements so becomes only 0.5 s. We show first Ne and Te estimates from the EFI LPs obtained. The data feature very low instrumental noise thanks to the ripple technique. The LP data are compared with observations by incoherent scatter radars, namely EISCAT UHF, VHF, the ESR, and also Arecibo.