Modelling the enect of ferrite on an inductively coupled plasma torch: II. Finite ferrite permeability

摘要

A model for an inductively coupled plasma with ferrite around the coil is developed. Vector representation is used for modelling and calculation of the electromagnetic fields. The permeability of ferrite is taken into account (not assumed to be infinite as in a previous work by the authors) but is assumed not to change with magnetic fields. The power dissipation in ferrite is neglected (no imaginary part for permeability). Under these assumptions, the role of ferrite can be completely replaced by the magnetization current density on the surface of ferrite. Through the magnetic field boundary condition on the surface of ferrite, the magnetization current density is derived and added to vector potential equations as a source term. The commercial Computational Fluid Dynamics (CFD) software FLUENT is used to solve the governing equations of plasma flow with vector potential equation and the flow, temperature, and electromagnetic fields. The effect of different shapes of ferrites around the coil was simulated. The results are compared with the results from the same model without ferrite and a previously proposed model with infinite permeability of ferrite. The computation results show that the effect of ferrite is not only to shield the electromagnetic radiation but it also decreases the coil current necessary to sustain the same power plasma torch. Accordingly, it increases the power coupling efficiency as well. [References: 17]