Analysis of the enthalpy probe technique for thermal plasma diagnostics

An experimental analysis of the enthalpy probe technique for thermal plasma diagnostics is presented. Emphasis is given to the probe sensitivity, its accuracy, and its effect on the plasma flow. The study was carried out using a direct current (dc) plasma torch operated with Ar/H2 mixture (1% H2) under two different reactor chamber pressures, 400 and 200 torr. The results show that when the probe tip is coated with a thermal barrier coating, the sensitivity is improved because of the reduction of the tare heat flux to the probe surface. Thus, even at low values of gas sampling flow rate, the probe can still provide measurements with acceptable accuracy while the isokinetic sampling condition continues to be respected. Emission spectroscopic results show that the probe has negligible effect on the temperature field of the plasma jet. copyright 1995 American Institute of Physics