Left: interior of the PEPSO plasma chamber, with the mutual impedance antennas (orange) and pre-amplifiers (yellow), the Langmuir probe (red), the plasma source (green), and the inlet for the vacuum pumps (violet). The Langmuir probe in the retracted position is hidden in the hole located on the right, at the support base. Right: three-dimensional mesh used to discretize the PEPSO plasma chamber in the DSCD mutual impedance numerical model. The pair of electrodes of the emitting (receiving) antenna are indicated as E₁ and E₂ (R₁, R₂).