Low Pressure Plasma Spraying or Vacuum Plasma Spraying make use of plasma torches operated inside a vessel under reduced pressure. The supersonic propagation of the plasma jets in a low pressure atmosphere requires special care during use in order to guarantee the desired properties with regard to the flow. This paper presents measurements of parameters of the plasma jet at different gas pressures. It shows the effect of chamber pressure on the jet expansion characteristics by imaging of the plasma jet structure and measurements of the nozzle exit pressure. Enthalpy probe measurements are presented for the high side of the pressure range investigated, and have been used to validate simulations presented in an associated paper. Paper includes a German-language abstract.