Temperature measurement of an atmospheric-pressure plasma torch

A simple method to make a temperature measurement in an atmospheric-pressur e plasma torch with a density of 10(13) electrons/cm(3) is developed. The m ethod is based on thermal equilibrium and a detailed analysis of heat loss from a copper wire placed in a torch. The wire diameter, which regulates he at loss, is systematically reduced to increase the temperature of the wire segment in the torch. This process yields a critical wire diameter: Smaller diameters melt and larger diameters are not affected. For the critical dia meter the wire temperature in the torch is approximated as the wire melting temperature. This temperature and an analysis of heat input from the torch and heat loss from the wire combine to provide a temperature measurement i n the 1300-2200 K range. Using this technique, the temperature of a plasma torch was determined to be approximately 1760 K. (C) 1999 American Institut e of Physics. [S0034-6748(99)03407-3].