Modelling the effect of ferrite on an inductively coupled plasma torch: I. Infinite ferrite permeability

A new model for electromagnetic field modelling is proposed for the simulation of inductive plasma torches. Instead of solving the equations of vector potential, the electromagnetic fields are obtained by solving the equations of the magnetic stream function (ψ), the contours of which represent the magnetic lines, i.e. the direction of magnetic field. This model is used to calculate the effect of ferrite on the plasma flow when the ferrite is placed around the coil in order to shield the electromagnetic radiation, therefore reducing the losses of RF power. Under the assumption that the permeability of ferrite is infinite, the magnetic line is perpendicular to the surface of ferrite. If the ferrite has infinite permeability, we need not solve the equations of magnetic stream function in the ferrite and the surfaces of ferrite are taken as the boundary of the magnetic stream function at which the normal derivative of magnetic stream function is set to zero. In this paper, the computational results with different ferrite shapes have been obtained, which show that the role of ferrite is not only to shield electromagnetic radiation but it also increases the power coupling efficiency to plasma torch and reduces the necessary coil current as well. The results of the model clearly indicate how this can be done efficiently in an industrial plasma torch. (author)