An experimental apparatus designed for studying reaction processes in high temperature plasmas is described. An rf induction plasma produced at gas temperatures from 1000 to 4000 K is passed through a reaction channel at sonic velocity where it reacts with supersonically injected target gas molecules. Pressures in the reaction channel can be varied from 25 to 125 Torr. The plasma, together with the reaction products, undergoes a free jet expansion into a vacuum chamber at 0.2 Torr where the expansion core flow is sampled by a molecular beam mass sampling system using a quadrupole mass spectrometer for analysis. The electron density in the free jet is measured with a Kahyphen;band interferometer. The electron temperature in the plasma source and reaction channel is measured spectroscopically; in addition, the electron temperature in the source is monitored with an Xhyphen;band radiometer. The change in the electron density, together with the change in the intensity of the positive and negative ion signals as a function of the number of target gas molecules injected, is used to evaluate the reaction rates. Examples of electron attachment rate measurements in N2Osngbnd;Ar and SF6sngbnd;Ar mixtures at 3000 K are given.
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