Supersonic argon flow in an arc plasma source
Résumé
A stationary plasma flow is obtained in a vacuum chamber from a D.C. arc-jet operating with argon. Typically, the plasma source operates with an electric input power of 10 kW (discharge current of 100A) and with a mass flow rate of 0.1 mg/s. The axi-symmetric nozzle of the arc-jet presents a cylindrical throast where the sustained arc is standing between the plane tip of a cathode made of thoriated tungsten or made of zirconium depending on the used gas and the convergent-throast-divergent nozzle made of copper used as anode. This plasma source generates a supersonic flow of plasma with an electron energy around 1eV and a plasma density around 1011-1012 el/cm3. The plasma flow in the arc-jet source is described by the Navier-Stokes (Bordeaux - France). This numerical code takes into account non equilibrium chemical processes and dissipative effects (viscosity, diffusion, heat conduction). It is used for the description of argon plasma in the D.C. arc-jet of the Laboratoire of Aérothermique. The chemical processes involve different states of the atoms of Ar and Ar+ and the transport coefficients are described from the update descriptions for the potentials of interaction between the different species. Full catalytic or non catalytic conditions are used for the surface of the anode and a thermal equilibrium is assumed between the different kinetic temperatures (Tj = Te). The plasma flow parameters (T, V, p, Ρ, ne) are calculated for different operating conditions of the arc-jet (electric power, mass flow rate) in the throat of the nozzle and in its conical divergent part. The relaxation of the different physical processes inside the nozzle and the evolution of the Mach number are analyzed with different approach: Navier-Stokes, Euler and 1D. The calculated electron temperature and plasma density are compared with measurements performed in the facility.