At the Institute for Space Systems three plasma wind tunnels for the simulation of conditions encountered by space vehicles during planetary entry are available. Two of these tunnels are equipped with a magnetoplasmadynamic accelerator, specially designed for the use of gas mixtures such as N2/O2 and carbon-containing gas mixtures. A quadrupole mass spectrometer that is placed inside the plasma jet is used to determine the plasma composition, the radial and axial distributions of all neutral and ionized particles, as well as the ion energy distributions. A theoretical investigation of the influence of the orifice opening on the sampling of radicals leads to a correction factor, with which the effect of recombination losses inside the orifice can be estimated. Additionally, a model of the space charge sheath in front of the orifice yields an equation for the evaluation of the ion temperatures. Different plasma conditions at ambient pressures of 0.1-2.9 mbar and at specific enthalpies of 19-33 MJ/kg were investigated. Nomenclature