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Title: Numerical model of the plasma formation at electron beam welding

The model of plasma formation in the keyhole in liquid metal as well as above the electron beam welding zone is described. The model is based on solution of two equations for the density of electrons and the mean electron energy. The mass transfer of heavy plasma particles (neutral atoms, excited atoms, and ions) is taken into account in the analysis by the diffusion equation for a multicomponent mixture. The electrostatic field is calculated using the Poisson equation. Thermionic electron emission is calculated for the keyhole wall. The ionization intensity of the vapors due to beam electrons and high-energy secondary and backscattered electrons is calibrated using the plasma parameters when there is no polarized collector electrode above the welding zone. The calculated data are in good agreement with experimental data. Results for the plasma parameters for excitation of a non-independent discharge are given. It is shown that there is a need to take into account the effect of a strong electric field near the keyhole walls on electron emission (the Schottky effect) in the calculation of the current for a non-independent discharge (hot cathode gas discharge). The calculated electron drift velocities are much bigger than the velocity at which currentmore » instabilities arise. This confirms the hypothesis for ion-acoustic instabilities, observed experimentally in previous research.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. The Department for Applied Physics, Perm National Research Polytechnic University, Perm 614990 (Russian Federation)
  2. (Russian Federation)
  3. Institute of Electronics, Bulgarian Academy of Sciences, 72 Tzarigradsko Shose, 1784 Sofia (Bulgaria)
  4. (Bulgaria)
Publication Date:
OSTI Identifier:
22399196
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 1; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ATOMS; CATHODES; DIFFUSION EQUATIONS; ELECTRIC CURRENTS; ELECTRIC FIELDS; ELECTRON BEAM WELDING; ELECTRON DRIFT; ELECTRON EMISSION; ELECTRONS; EXCITATION; IONS; LIQUID METALS; MASS TRANSFER; MATHEMATICAL SOLUTIONS; PLASMA; PLASMA INSTABILITY; POISSON EQUATION; SCHOTTKY EFFECT; VAPORS