A MEASUREMENT OF AXIAL VELOCITY AND TEMPERATURE IN A FREE-BURNING ARCUSING THOMSON SCATTERING

High-resolution lineshape analysis of Thomson-scattered laser light wa s used to determine the centreline temperature and velocity of ions in a free-burning are. The are was maintained at 200 A(dc) in atmospheri c-pressure argon. The technique allows direct measurement of plasma ga s velocity without disturbing conditions within the plasma-the values found were lower than previously reported using indirect methods and i ncreased with time, over 2 h. On the other hand, the ion temperature w as found to drift little over the same period and its value was higher than previously reported for Thomson scattering, yet lower than found by emission spectroscopy. Possible reasons for these differences are examined and, in particular, the role of small concentrations of oxyge n is discussed. This preliminary study highlights experimental difficu lties that are inherent in this type of measurement.