Laser thomson scattering measurements in the anode boundary lyaer of high intensity arcs

Summary form only given. Anode boundary layers of high intensity arcs are important for many industrial applications, such as plasma spray torches. In this study, laser Thomson scattering has been used to measure the distributions of the electron temperature and the electron density in the anode boundary layer of an atmospheric pressure, high intensity transferred argon arc. The electron temperature and the electron density up to a position 0.1 mm from the anode have been obtained. Two theories (random phase approximation (RPA) and memory function formalism (MFF)) for evaluating the scattering signal have been compared. It has been found that the RPA and the MFF yield electron temperature values which are close, while the MFF yields electron densities about 30% higher than the RPA. The measurements were performed with a wide range of plasma gas flow rates (2 slpm to 15 slpm) and arc currents (60 A to 100 A) to obtain data for both diffuse anode attachment and constricted anode attachment. For a typical diffuse attachment, the electron temperature remains high (>9000 K) and has a sharp drop (25%) in a region less than 0.5 mm from the anode. This result is in good agreement with previous Langmuir probe measurements. The electron density remains high after a 50% decrease in a region 2 mm from the anode. For a typical constricted attachment, the electron temperature first drops slowly in the anode boundary layer and shows an increase from a position about 0.5 mm from the anode. The electron density values are lower than in the case of a diffuse arc. The changes of the electron temperature and the electron density distributions when a cold gas flow is introduced parallel to the anode are also presented