Transition Between Anode Attachment Modes in a High Intensity Transferred Argon Arc

Summary form only given. The anode attachments in a high intensity transferred argon arc at atmospheric pressure have been investigated experimentally. With fixed arc current (100 A), reducing plasma working gas flow rate has been used to realize the transition from the well-known diffuse attachment mode to the constricted attachment mode. Two transition modes have been found, namely a lift-up mode and a multiple-attachment mode. Two-dimensional electron temperature and electron density maps for these modes have been measured with a laser Thomson scattering system, which can characterize the plasma 0.05 mm in front of the anode surface. In the center of a diffuse attachment and in the center of a constricted attachment, the electron temperatures are ~9000 K and >12000 K and the electron densities are ~10 22 m -3 and >2* 10 22 m -3 , respectively. The current density maps and the electric field maps are obtained, for the first time, by solving the charge-continuity equation based on the experimental data. The results show that in the center of a diffuse attachment and in center of a constricted attachment, the current densities on the anode surface are ~10 6 A/m 2 and ~5*10 6 A/m 2 , respectively. Moreover, negative anode fall exists in a diffuse attachment, while positive anode fall exists in a constricted attachment. In the fringes of a constricted attachment, complicated electric field distributions have been observed due to the strong gradients. A linear instability analysis has also been performed and the results suggest that the transition between the anode attachment modes may be initiated by the accelerating electric field to electrons in the fringes in a lift-up mode, which encourages the electron overheating instability to develop.