Formation and expansion of the plasma column under electron beam-metal interaction

The process of expansion of low-energy electrons and ions produced from electron beam evaporation of a metal target in the technological vacuum chamber of an electron beam welding machine is studied. Analyzing the spatial distribution of the particle density that is measured, the radial collisionless plasma motion from the beam region is shown to be prevailing. A model of the free plasma expansion out of the cylindrical source is developed. The relative distribution of the electron density and the electrostatic potential obtained are compared with the experimental results. The knowledge of the plasma parameter distributions in the technological vacuum chamber can be used for remote diagnostics and control of the technology process.