A two-temperature model for a microwave generated plasma jet

Summary form only given. The plasma jet under investigation is generated by a microwave discharge in high-speed argon gas flow operating at 896 MHz. Recent spectroscopic results show that the plasma state deviates from local thermodynamic equilibrium (LTE). This is because the energy acquired by the electrons from the microwave fields cannot be readily transferred to the heavy particles. It is anticipated that the electron temperature will be higher than the translational temperature of the heavy particles A two-temperature model is thus developed to simulate the plasma behaviour of the system under practical working conditions. The electron and the heavy particles are treated as two different perfect gases. Maxwell-Boltzmann distribution shall prevail among electrons as well as among heavy particles, but with different temperatures. The electromagnetic field distribution inside the cavity and around the nozzle is computed using finite-difference time domain (FDTD) method. An iterative process is used to compute the self-consistent solutions of the electromagnetic fields and plasma properties. The two-temperature plasma model predicts a much higher electron temperature than that of the heavy particles, which is consistent with our experimental results. It is also shown that gas flow from the nozzle plays an important role in stabilizing the microwave plasma jet because electron diffusion towards the ambient tends to expand the discharge, thus making the plasma jet unsustainable. The plasma jet interacts with the work piece and supplies energy for melting and cutting processes. By using this model, the performance of the plasma jet system will be optimized in terms of the energy and momentum fluxes that are delivered to the work piece.