Thermal plasma processes are now currently used in industry for manyapplications, each of them using adapted plasma torches or transferred arcs.However, many difficulties still exist in understanding what happens at theelectrodes of direct current (dc) arcs. For the latter the materialcomposition is continuously evolving and the arc root behaviour is athree-dimensional transient phenomenon. For RF discharges, the couplingbetween the plasma and the discharge is much better understood.To model such flows, knowledge of the transport properties is a prerequisiteand many works are in progress in this field. The difficulty in modelling liesin the fact that the plasma core is laminar while its fringes are turbulent.Moreover, the turbulence is more of the engulfment type than represented byk-ε, Rij... models and the phenomena are even morecomplex with arcs due to the piston flow generated by arc root fluctuations.Mixing a cold gas with the plasma is the key of many processes. Here alsothree-dimensional codes are now currently used but it is still difficult tointroduce the transient behaviour of the plasma and calculate, fast enough,the-out-of-equilibrium composition and transport coefficients of complexmixtures.Models have been backed by measuring techniques: emission or absorptionspectroscopy, enthalpy probes of reduced sizes (d~3 mm) coupled with amass spectrometer, laser scattering techniques, fast imaging, with or withoutlaser illumination, laser anemometry, fast (50 ns) pyrometry for particles inflight. Such techniques give a much better idea of local and/or transientphenomena, but they also confirm the need for the development of new models.
Magnetic filter operation in hydrogen plasmas